blocks|key|3876801|text|在C标准中没有这样做的函数。符合POSIX的Unix系统要求在头strings.h中有strcasecmp；微软系统有stricmp。为了便于移植，可以编写自己的代码：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3876802|int+strcicmp(char+const+*a,+char+const+*b)
{
++++for+(;;+a%2B%2B,+b%2B%2B)+{
++++++++int+d+=+tolower((unsigned+char)*a)+-+tolower((unsigned+char)*b);
++++++++if+(d+!=+0+%7C%7C+!*a)
++++++++++++return+d;
++++}
}|code-block|syntax|javascript|3876803|但请注意，这些解决方案都不能处理UTF-8字符串，只能处理ASCII字符串。|3876804|entityMap|0|LINK|mutability|MUTABLE|url|http://pubs.opengroup.org/onlinepubs/9699919799/functions/strcasecmp.html^0|W|9|17|A|1N|7|17|A|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@$9|11|A|12|1|13]]|E|$]]|$1|F|3|G|5|H|7|14|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|15|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

There is no function that does this in the C standard. Unix systems that comply with POSIX are required to have <a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/strcasecmp.html" rel="noreferrer"><code>strcasecmp</code></a> in the header <code>strings.h</code>; Microsoft systems have <code>stricmp</code>. To be on the portable side, write your own:

<pre><code>int strcicmp(char const *a, char const *b)
{
 for (;; a++, b++) {
 int d = tolower((unsigned char)*a) - tolower((unsigned char)*b);
 if (d != 0 || !*a)
 return d;
 }
}
</code></pre>

But note that none of these solutions will work with UTF-8 strings, only ASCII ones.

blocks|key|1766144|text|看看strings.h中的strcasecmp()。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1766145|entityMap|0|LINK|mutability|MUTABLE|url|https://www.ibm.com/support/knowledgecenter/en/ssw_ibm_i_72/rtref/strcasecmp.htm^0|2|9|D|C|D|C|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]|$9|Q|A|R|B|C]]|D|@$9|S|A|T|1|U]]|E|$]]|$1|F|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

Take a look at <a href="https://www.ibm.com/support/knowledgecenter/en/ssw_ibm_i_72/rtref/strcasecmp.htm" rel="noreferrer"><code>strcasecmp()</code></a> in <code>strings.h</code>.

blocks|key|3876868|text|我发现了名为from的内置方法，它在标准头文件中包含额外的字符串函数。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3876869|下面是相关的签名：|3876870|int++strcasecmp(const+char+*,+const+char+*);
int++strncasecmp(const+char+*,+const+char+*,+size_t);|code-block|syntax|javascript|3876871|我还在xnu内核中找到了它的同义词(osfmk/device/subrs.c)，并且在下面的代码中实现了它，因此与原始的strcmp函数相比，您不会期望在数量上有任何行为变化。|3876872|tolower(unsigned+char+ch)+{
++++if+(ch+>=+'A'+&&+ch+<=+'Z')
++++++++ch+=+'a'+%2B+(ch+-+'A');
++++return+ch;
+}

int+strcasecmp(const+char+*s1,+const+char+*s2)+{
++++const+unsigned+char+*us1+=+(const+u_char+*)s1,
++++++++++++++++++++++++*us2+=+(const+u_char+*)s2;

++++while+(tolower(*us1)+==+tolower(*us2%2B%2B))
++++++++if+(*us1%2B%2B+==+'\0')
++++++++++++return+(0);
++++return+(tolower(*us1)+-+tolower(*--us2));
}|3876873|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I've found built-in such method named from which contains additional string functions to the standard header . 

Here's the relevant signatures : 

<pre><code>int strcasecmp(const char *, const char *);
int strncasecmp(const char *, const char *, size_t);
</code></pre>

I also found it's synonym in xnu kernel (osfmk/device/subrs.c) and it's implemented in the following code, so you wouldn't expect to have any change of behavior in number compared to the original strcmp function. 

<pre><code>tolower(unsigned char ch) {
 if (ch &gt;= 'A' &amp;&amp; ch &lt;= 'Z')
 ch = 'a' + (ch - 'A');
 return ch;
 }

int strcasecmp(const char *s1, const char *s2) {
 const unsigned char *us1 = (const u_char *)s1,
 *us2 = (const u_char *)s2;

 while (tolower(*us1) == tolower(*us2++))
 if (*us1++ == '\0')
 return (0);
 return (tolower(*us1) - tolower(*--us2));
}
</code></pre>

blocks|key|3876779|text|我会使用stricmp()。它比较两个字符串而不考虑大小写。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3876780|请注意，在某些情况下，将字符串转换为小写可能会更快。|3876781|entityMap^0|4|9|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|M|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|N|8|@]|D|@]|E|$]]]|I|$]]

I would use <code>stricmp()</code>. It compares two strings without regard to case.

Note that, in some cases, converting the string to lower case can be faster.

blocks|key|5294007|text|执行不区分大小写的比较时需要注意的其他陷阱：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5294008|5294009|比较是小写还是大写？(足够常见的问题)|offset|length|style|BOLD|5294010|使用strcicmpL("A",+"a")和strcicmpU("A",+"a")，下面的两个函数都将返回0。|CODE|5294011|然而，strcicmpL("A",+"_")和strcicmpU("A",+"_")可以返回不同的带符号结果，因为'_'通常在大小写字母之间。|5294012|这会影响与qsort(...,+...,+...,+strcicmp)一起使用时的排序顺序。非标准库C函数，如常用的stricmp()或strcasecmp()，往往定义良好，并倾向于通过小写进行比较。然而，变化是存在的。|5294013|int+strcicmpL(char+const+*a,+char+const+*b)+{
++while+(*b)+{
++++int+d+=+tolower(*a)+-+tolower(*b);
++++if+(d)+{
++++++++return+d;
++++}+
++++a%2B%2B;
++++b%2B%2B;
++}+
++return+tolower(*a);
}

int+strcicmpU(char+const+*a,+char+const+*b)+{
++while+(*b)+{
++++int+d+=+toupper(*a)+-+toupper(*b);
++++if+(d)+{
++++++++return+d;
++++}+
++++a%2B%2B;
++++b%2B%2B;
++}+
++return+toupper(*a);
}|code-block|syntax|javascript|5294014|5294015|char+可以为负值。(并非罕见)|5294016|为unsigned+char值和负EOF指定touppper(int)和tolower(int)。此外，strcmp()会返回结果，就好像每个char都被转换为unsigned+char一样，而不管char是有符号的还是无符号的。|5294017|tolower(*a);+//+Potential+UB
tolower((unsigned+char)+*a);+//+Correct+(Almost+-+see+following)|5294018|5294019|char+可以是负值，但不能是2的补码。(罕见)|5294020|由于位模式应解释为unsigned+char，因此上述代码不能正确处理-0或其他负值。要正确处理所有整数编码，请首先更改指针类型。|5294021|//+tolower((unsigned+char)+*a);
tolower(*(const+unsigned+char+*)a);+//+Correct|5294022|5294023|语言环境(不太常见)|5294024|尽管使用ASCII代码(0-127)的字符集非常普遍，但其余的代码往往存在特定于区域设置的问题。因此，strcasecmp("\xE4",+"a")可能在一个系统上返回0，而在另一个系统上返回非零值。|5294025|5294026|Unicode+(未来之路)|5294027|如果解决方案需要处理的不仅仅是ASCII，那么可以考虑使用unicode_strcicmp()。由于C+lib不提供这样的函数，因此推荐使用某个备用库中的预编码函数。编写自己的unicode_strcicmp()是一项艰巨的任务。|5294028|5294029|所有的字母都是从下到上映射的吗？(书面语)|5294030|a-z与A-Z一对一映射，而不同的语言环境将各种小写字符映射为一个大写字符，反之亦然。此外，一些大写字符可能缺少小写等效项，反之亦然。|5294031|这使得代码必须同时通过tolower()和tolower()进行转换。|5294032|int+d+=+tolower(toupper(*a))+-+tolower(toupper(*b));|5294033|同样，如果代码tolower(toupper(*a))与toupper(tolower(*a))相比，可能会产生不同的排序结果。|5294034|5294035|可移植性|5294036|@B.+Nadolson建议避免使用自己的strcicmp()，这是合理的，除非代码需要高度等效的可移植功能。|5294037|下面是一种甚至比某些系统提供的功能执行得更快的方法。它通过使用与'\0'不同的两个不同的表，对每个循环执行一次比较，而不是两次比较。您的结果可能有所不同。|5294038|static+unsigned+char+low1[UCHAR_MAX+%2B+1]+=+{
++0,+1,+2,+3,+...
++'@',+'a',+'b',+'c',+...+'z',+`[`,+...++//+@ABC...+Z[...
++'`',+'a',+'b',+'c',+...+'z',+`{`,+...++//+`abc...+z{...
}
static+unsigned+char+low2[UCHAR_MAX+%2B+1]+=+{
//+v---+Not+zero,+but+A+which+matches+none+in+`low1[]`
++'A',+1,+2,+3,+...
++'@',+'a',+'b',+'c',+...+'z',+`[`,+...
++'`',+'a',+'b',+'c',+...+'z',+`{`,+...
}

int+strcicmp_ch(char+const+*a,+char+const+*b)+{
++//+compare+using+tables+that+differ+slightly.
++while+(low1[*(const+unsigned+char+*)a]+==+low2[*(const+unsigned+char+*)b])+{
++++a%2B%2B;
++++b%2B%2B;
++}
++//+Either+strings+differ+or+null+character+detected.
++//+Perform+subtraction+using+same+table.
++return+(low1[*(const+unsigned+char+*)a]+-+low1[*(const+unsigned+char+*)b]);
}|5294039|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/5820810/case-insensitive-string-comp-in-c#comment45276351_5820991^0|0|0|0|J|0|2|J|M|J|0|3|J|N|J|1L|3|0|5|U|1M|9|1W|C|0|0|0|0|4|5|C|0|4|0|1|D|H|3|M|D|10|C|1G|8|1Z|4|28|D|2R|4|0|0|0|0|4|5|J|0|4|0|9|D|Z|2|0|0|0|0|A|0|1F|N|0|0|0|E|0|T|I|2G|I|0|0|0|L|0|0|B|9|L|9|0|0|7|K|S|K|0|0|0|4|0|L|A|0|C|0|0|W|4|0|0^^$0|@$1|2|3|4|5|6|7|2A|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|2B|8|@]|9|@]|A|$]]|$1|C|3|D|5|6|7|2C|8|@$E|2D|F|2E|G|H]]|9|@]|A|$]]|$1|I|3|J|5|6|7|2F|8|@$E|2G|F|2H|G|K]|$E|2I|F|2J|G|K]]|9|@]|A|$]]|$1|L|3|M|5|6|7|2K|8|@$E|2L|F|2M|G|K]|$E|2N|F|2O|G|K]|$E|2P|F|2Q|G|K]]|9|@]|A|$]]|$1|N|3|O|5|6|7|2R|8|@$E|2S|F|2T|G|K]|$E|2U|F|2V|G|K]|$E|2W|F|2X|G|K]]|9|@]|A|$]]|$1|P|3|Q|5|R|7|2Y|8|@]|9|@]|A|$S|T]]|$1|U|3|-4|5|6|7|2Z|8|@]|9|@]|A|$]]|$1|V|3|W|5|6|7|30|8|@$E|31|F|32|G|H]|$E|33|F|34|G|H]|$E|35|F|36|G|K]]|9|@]|A|$]]|$1|X|3|Y|5|6|7|37|8|@$E|38|F|39|G|K]|$E|3A|F|3B|G|K]|$E|3C|F|3D|G|K]|$E|3E|F|3F|G|K]|$E|3G|F|3H|G|K]|$E|3I|F|3J|G|K]|$E|3K|F|3L|G|K]|$E|3M|F|3N|G|K]]|9|@]|A|$]]|$1|Z|3|10|5|R|7|3O|8|@]|9|@]|A|$S|T]]|$1|11|3|-4|5|6|7|3P|8|@]|9|@]|A|$]]|$1|12|3|13|5|6|7|3Q|8|@$E|3R|F|3S|G|H]|$E|3T|F|3U|G|H]|$E|3V|F|3W|G|K]]|9|@]|A|$]]|$1|14|3|15|5|6|7|3X|8|@$E|3Y|F|3Z|G|K]|$E|40|F|41|G|K]]|9|@]|A|$]]|$1|16|3|17|5|R|7|42|8|@]|9|@]|A|$S|T]]|$1|18|3|-4|5|6|7|43|8|@]|9|@]|A|$]]|$1|19|3|1A|5|6|7|44|8|@$E|45|F|46|G|H]]|9|@]|A|$]]|$1|1B|3|1C|5|6|7|47|8|@$E|48|F|49|G|K]]|9|@]|A|$]]|$1|1D|3|-4|5|6|7|4A|8|@]|9|@]|A|$]]|$1|1E|3|1F|5|6|7|4B|8|@$E|4C|F|4D|G|H]]|9|@]|A|$]]|$1|1G|3|1H|5|6|7|4E|8|@$E|4F|F|4G|G|K]|$E|4H|F|4I|G|K]]|9|@]|A|$]]|$1|1I|3|-4|5|6|7|4J|8|@]|9|@]|A|$]]|$1|1J|3|1K|5|6|7|4K|8|@$E|4L|F|4M|G|H]]|9|@]|A|$]]|$1|1L|3|1M|5|6|7|4N|8|@]|9|@]|A|$]]|$1|1N|3|1O|5|6|7|4O|8|@$E|4P|F|4Q|G|K]|$E|4R|F|4S|G|K]]|9|@]|A|$]]|$1|1P|3|1Q|5|R|7|4T|8|@]|9|@]|A|$S|T]]|$1|1R|3|1S|5|6|7|4U|8|@$E|4V|F|4W|G|K]|$E|4X|F|4Y|G|K]]|9|@]|A|$]]|$1|1T|3|-4|5|6|7|4Z|8|@]|9|@]|A|$]]|$1|1U|3|1V|5|6|7|50|8|@$E|51|F|52|G|H]]|9|@]|A|$]]|$1|1W|3|1X|5|6|7|53|8|@$E|54|F|55|G|K]]|9|@$E|56|F|57|1|58]]|A|$]]|$1|1Y|3|1Z|5|6|7|59|8|@$E|5A|F|5B|G|K]]|9|@]|A|$]]|$1|20|3|21|5|R|7|5C|8|@]|9|@]|A|$S|T]]|$1|22|3|-4|5|6|7|5D|8|@]|9|@]|A|$]]]|23|$24|$5|25|26|27|A|$28|29]]]]

<h1>Additional pitfalls to watch out for when doing case insensitive compares:</h1>
<hr />
Comparing as lower or as upper case? (common enough issue)
Both below will return 0 with <code>strcicmpL(&quot;A&quot;, &quot;a&quot;)</code> and <code>strcicmpU(&quot;A&quot;, &quot;a&quot;)</code>. 
Yet <code>strcicmpL(&quot;A&quot;, &quot;_&quot;)</code> and <code>strcicmpU(&quot;A&quot;, &quot;_&quot;)</code> can return different signed results as <code>'_'</code> is often between the upper and lower case letters.
This affects the sort order when used with <code>qsort(..., ..., ..., strcicmp)</code>. Non-standard library C functions like the commonly available <code>stricmp()</code> or <code>strcasecmp()</code> tend to be well defined and favor comparing via lowercase. Yet variations exist.
<pre><code>int strcicmpL(char const *a, char const *b) {
 while (*b) {
 int d = tolower(*a) - tolower(*b);
 if (d) {
 return d;
 } 
 a++;
 b++;
 } 
 return tolower(*a);
}

int strcicmpU(char const *a, char const *b) {
 while (*b) {
 int d = toupper(*a) - toupper(*b);
 if (d) {
 return d;
 } 
 a++;
 b++;
 } 
 return toupper(*a);
}
</code></pre>
<hr />
<code>char</code> can have a negative value. (not rare)
<code>touppper(int)</code> and <code>tolower(int)</code> are specified for <code>unsigned char</code> values and the negative <code>EOF</code>. Further, <code>strcmp()</code> returns results as if each <code>char</code> was converted to <code>unsigned char</code>, regardless if <code>char</code> is signed or unsigned.
<pre><code>tolower(*a); // Potential UB
tolower((unsigned char) *a); // Correct (Almost - see following)
</code></pre>
<hr />
<code>char</code> can have a negative value and not 2's complement. (rare)
The above does not handle <code>-0</code> nor other negative values properly as the bit pattern should be interpreted as <code>unsigned char</code>. To properly handle all integer encodings, change the pointer type first.
<pre><code>// tolower((unsigned char) *a);
tolower(*(const unsigned char *)a); // Correct
</code></pre>
<hr />
Locale (less common)
Although character sets using ASCII code (0-127) are ubiquitous, the remainder codes tend to have locale specific issues. So <code>strcasecmp(&quot;\xE4&quot;, &quot;a&quot;)</code> might return a 0 on one system and non-zero on another.
<hr />
Unicode (the way of the future)
If a solution needs to handle more than ASCII consider a <code>unicode_strcicmp()</code>. As C lib does not provide such a function, a pre-coded function from some alternate library is recommended. Writing your own <code>unicode_strcicmp()</code> is a daunting task.
<hr />
Do all letters map one lower to one upper? (pedantic)
[A-Z] maps one-to-one with [a-z], yet various locales map various lower case chracters to one upper and visa-versa. Further, some uppercase characters may lack a lower case equivalent and again, visa-versa.
This obliges code to covert through both <code>tolower()</code> and <code>tolower()</code>.
<pre><code>int d = tolower(toupper(*a)) - tolower(toupper(*b));
</code></pre>
Again, potential different results for sorting if code did <code>tolower(toupper(*a))</code> vs. <code>toupper(tolower(*a))</code>.
<hr />
Portability
<a href="https://stackoverflow.com/questions/5820810/case-insensitive-string-comp-in-c#comment45276351_5820991">@B. Nadolson</a> recommends to avoid rolling your own <code>strcicmp()</code> and this is reasonable, except when code needs high equivalent portable functionality.
Below is an approach that even performed faster than some system provided functions. It does a single compare per loop rather than two by using 2 different tables that differ with <code>'\0'</code>. Your results may vary.
<pre><code>static unsigned char low1[UCHAR_MAX + 1] = {
 0, 1, 2, 3, ...
 '@', 'a', 'b', 'c', ... 'z', `[`, ... // @ABC... Z[...
 '`', 'a', 'b', 'c', ... 'z', `{`, ... // `abc... z{...
}
static unsigned char low2[UCHAR_MAX + 1] = {
// v--- Not zero, but A which matches none in `low1[]`
 'A', 1, 2, 3, ...
 '@', 'a', 'b', 'c', ... 'z', `[`, ...
 '`', 'a', 'b', 'c', ... 'z', `{`, ...
}

int strcicmp_ch(char const *a, char const *b) {
 // compare using tables that differ slightly.
 while (low1[*(const unsigned char *)a] == low2[*(const unsigned char *)b]) {
 a++;
 b++;
 }
 // Either strings differ or null character detected.
 // Perform subtraction using same table.
 return (low1[*(const unsigned char *)a] - low1[*(const unsigned char *)b]);
}
</code></pre>

blocks|key|1501465|text|我并不是most-upvoted+answer+here的粉丝(部分原因是它似乎不正确，因为如果它在任一字符串中读取空终止符--但不是同时读取两个字符串中的空终止符--它就应该执行continue操作--而且它不会这样做)，所以我编写了自己的代码。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1501466|这是对strncmp()的直接替代，并且已经用大量测试用例进行了测试，如下所示。|1501467|它与strncmp()相同，除了：|1501468|如果任一字符串为case-insensitive.|1501469|The，则|unordered-list-item|1501470|It+is+null行为不是未定义的(它是明确定义的)。如果任一字符串为null+ptr，则常规strncmp()具有未定义的行为(请参阅:如果任一输入字符串为NULL+ptr，则INT_MIN将作为特殊标记错误值返回。|ordered-list-item|1501471|1501472|1501473|限制:请注意，此代码适用于原始+(十进制值0到127，包括0和127)，而不适用于字符，例如unicode字符编码+(最常用)、和。|1501474|这里的只是代码(没有注释)：|BOLD|1501475|int+strncmpci(const+char+*+str1,+const+char+*+str2,+size_t+num)
{
++++int+ret_code+=+0;
++++size_t+chars_compared+=+0;

++++if+(!str1+%7C%7C+!str2)
++++{
++++++++ret_code+=+INT_MIN;
++++++++return+ret_code;
++++}

++++while+((chars_compared+<+num)+&&+(*str1+%7C%7C+*str2))
++++{
++++++++ret_code+=+tolower((int)(*str1))+-+tolower((int)(*str2));
++++++++if+(ret_code+!=+0)
++++++++{
++++++++++++break;
++++++++}
++++++++chars_compared%2B%2B;
++++++++str1%2B%2B;
++++++++str2%2B%2B;
++++}

++++return+ret_code;
}|code-block|syntax|javascript|1501476|全注释版本：|1501477|///+\brief++++++Perform+a+case-insensitive+string+compare+(`strncmp()`+case-insensitive)+to+see
///+++++++++++++if+two+C-strings+are+equal.
///+\note+++++++1.+Identical+to+`strncmp()`+except:
///+++++++++++++++1.+It+is+case-insensitive.
///+++++++++++++++2.+The+behavior+is+NOT+undefined+(it+is+well-defined)+if+either+string+is+a+null
///+++++++++++++++ptr.+Regular+`strncmp()`+has+undefined+behavior+if+either+string+is+a+null+ptr
///+++++++++++++++(see:+https://en.cppreference.com/w/cpp/string/byte/strncmp).
///+++++++++++++++3.+It+returns+`INT_MIN`+as+a+special+sentinel+value+for+certain+errors.
///+++++++++++++-+Posted+as+an+answer+here:+https://stackoverflow.com/a/55293507/4561887.
///+++++++++++++++-+Aided/inspired,+in+part,+by+`strcicmp()`+here:
///+++++++++++++++++https://stackoverflow.com/a/5820991/4561887.
///+\param[in]++str1++++++++C+string+1+to+be+compared.
///+\param[in]++str2++++++++C+string+2+to+be+compared.
///+\param[in]++num+++++++++max+number+of+chars+to+compare
///+\return+++++A+comparison+code+(identical+to+`strncmp()`,+except+with+the+addition
///+++++++++++++of+`INT_MIN`+as+a+special+sentinel+value):
///
///+++++++++++++INT_MIN+(usually+-2147483648+for+int32_t+integers)++Invalid+arguments+(one+or+both
///++++++++++++++++++++++of+the+input+strings+is+a+NULL+pointer).
///+++++++++++++<0+++++++The+first+character+that+does+not+match+has+a+lower+value+in+str1+than
///++++++++++++++++++++++in+str2.
///++++++++++++++0+++++++The+contents+of+both+strings+are+equal.
///+++++++++++++>0+++++++The+first+character+that+does+not+match+has+a+greater+value+in+str1+than
///++++++++++++++++++++++in+str2.
int+strncmpci(const+char+*+str1,+const+char+*+str2,+size_t+num)
{
++++int+ret_code+=+0;
++++size_t+chars_compared+=+0;

++++//+Check+for+NULL+pointers
++++if+(!str1+%7C%7C+!str2)
++++{
++++++++ret_code+=+INT_MIN;
++++++++return+ret_code;
++++}

++++//+Continue+doing+case-insensitive+comparisons,+one-character-at-a-time,+of+`str1`+to+`str2`,+so
++++//+long+as+1st:+we+have+not+yet+compared+the+requested+number+of+chars,+and+2nd:+the+next+char
++++//+of+at+least+*one*+of+the+strings+is+not+zero+(the+null+terminator+for+a+C-string),+meaning
++++//+that+string+still+has+more+characters+in+it.
++++//+Note:+you+MUST+check+`(chars_compared+<+num)`+FIRST+or+else+dereferencing+(reading)+`str1`+or
++++//+`str2`+via+`*str1`+and+`*str2`,+respectively,+is+undefined+behavior+if+you+are+reading+one+or
++++//+both+of+these+C-strings+outside+of+their+array+bounds.
++++while+((chars_compared+<+num)+&&+(*str1+%7C%7C+*str2))
++++{
++++++++ret_code+=+tolower((int)(*str1))+-+tolower((int)(*str2));
++++++++if+(ret_code+!=+0)
++++++++{
++++++++++++//+The+2+chars+just+compared+don't+match
++++++++++++break;
++++++++}
++++++++chars_compared%2B%2B;
++++++++str1%2B%2B;
++++++++str2%2B%2B;
++++}

++++return+ret_code;
}|1501478|测试代码：|1501479|从我的eRCaGuy_hello_world存储库下载包含单元测试的完整示例代码："strncmpci.c"|1501480|(这只是一小段)|1501481|int+main()
{
++++printf("-----------------------\n"
+++++++++++"String+Comparison+Tests\n"
+++++++++++"-----------------------\n\n");

++++int+num_failures_expected+=+0;

++++printf("INTENTIONAL+UNIT+TEST+FAILURE+to+show+what+a+unit+test+failure+looks+like!\n");
++++EXPECT_EQUALS(strncmpci("hey",+"HEY",+3),+'h'+-+'H');
++++num_failures_expected%2B%2B;
++++printf("------+beginning+------\n\n");


++++const+char+*+str1;
++++const+char+*+str2;
++++size_t+n;

++++//+NULL+ptr+checks
++++EXPECT_EQUALS(strncmpci(NULL,+"",+0),+INT_MIN);
++++EXPECT_EQUALS(strncmpci("",+NULL,+0),+INT_MIN);
++++EXPECT_EQUALS(strncmpci(NULL,+NULL,+0),+INT_MIN);
++++EXPECT_EQUALS(strncmpci(NULL,+"",+10),+INT_MIN);
++++EXPECT_EQUALS(strncmpci("",+NULL,+10),+INT_MIN);
++++EXPECT_EQUALS(strncmpci(NULL,+NULL,+10),+INT_MIN);

++++EXPECT_EQUALS(strncmpci("",+"",+0),+0);
++++EXPECT_EQUALS(strncmp("",+"",+0),+0);

++++str1+=+"";
++++str2+=+"";
++++n+=+0;
++++EXPECT_EQUALS(strncmpci(str1,+str2,+n),+0);
++++EXPECT_EQUALS(strncmp(str1,+str2,+n),+0);

++++str1+=+"hey";
++++str2+=+"HEY";
++++n+=+0;
++++EXPECT_EQUALS(strncmpci(str1,+str2,+n),+0);
++++EXPECT_EQUALS(strncmp(str1,+str2,+n),+0);

++++str1+=+"hey";
++++str2+=+"HEY";
++++n+=+3;
++++EXPECT_EQUALS(strncmpci(str1,+str2,+n),+0);
++++EXPECT_EQUALS(strncmp(str1,+str2,+n),+'h'+-+'H');

++++str1+=+"heY";
++++str2+=+"HeY";
++++n+=+3;
++++EXPECT_EQUALS(strncmpci(str1,+str2,+n),+0);
++++EXPECT_EQUALS(strncmp(str1,+str2,+n),+'h'+-+'H');

++++str1+=+"hey";
++++str2+=+"HEdY";
++++n+=+3;
++++EXPECT_EQUALS(strncmpci(str1,+str2,+n),+'y'+-+'d');
++++EXPECT_EQUALS(strncmp(str1,+str2,+n),+'h'+-+'H');

++++str1+=+"heY";
++++str2+=+"hEYd";
++++n+=+3;
++++EXPECT_EQUALS(strncmpci(str1,+str2,+n),+0);
++++EXPECT_EQUALS(strncmp(str1,+str2,+n),+'e'+-+'E');

++++str1+=+"heY";
++++str2+=+"heyd";
++++n+=+6;
++++EXPECT_EQUALS(strncmpci(str1,+str2,+n),+-'d');
++++EXPECT_EQUALS(strncmp(str1,+str2,+n),+'Y'+-+'y');

++++str1+=+"hey";
++++str2+=+"hey";
++++n+=+6;
++++EXPECT_EQUALS(strncmpci(str1,+str2,+n),+0);
++++EXPECT_EQUALS(strncmp(str1,+str2,+n),+0);

++++str1+=+"hey";
++++str2+=+"heyd";
++++n+=+6;
++++EXPECT_EQUALS(strncmpci(str1,+str2,+n),+-'d');
++++EXPECT_EQUALS(strncmp(str1,+str2,+n),+-'d');

++++str1+=+"hey";
++++str2+=+"heyd";
++++n+=+3;
++++EXPECT_EQUALS(strncmpci(str1,+str2,+n),+0);
++++EXPECT_EQUALS(strncmp(str1,+str2,+n),+0);

++++str1+=+"hEY";
++++str2+=+"heyYOU";
++++n+=+3;
++++EXPECT_EQUALS(strncmpci(str1,+str2,+n),+0);
++++EXPECT_EQUALS(strncmp(str1,+str2,+n),+'E'+-+'e');

++++str1+=+"hEY";
++++str2+=+"heyYOU";
++++n+=+10;
++++EXPECT_EQUALS(strncmpci(str1,+str2,+n),+-'y');
++++EXPECT_EQUALS(strncmp(str1,+str2,+n),+'E'+-+'e');

++++str1+=+"hEYHowAre";
++++str2+=+"heyYOU";
++++n+=+10;
++++EXPECT_EQUALS(strncmpci(str1,+str2,+n),+'h'+-+'y');
++++EXPECT_EQUALS(strncmp(str1,+str2,+n),+'E'+-+'e');

++++EXPECT_EQUALS(strncmpci("nice+to+meet+you.,;",+"NICE+TO+MEET+YOU.,;",+100),+0);
++++EXPECT_EQUALS(strncmp(++"nice+to+meet+you.,;",+"NICE+TO+MEET+YOU.,;",+100),+'n'+-+'N');
++++EXPECT_EQUALS(strncmp(++"nice+to+meet+you.,;",+"nice+to+meet+you.,;",+100),+0);

++++EXPECT_EQUALS(strncmpci("nice+to+meet+you.,;",+"NICE+TO+UEET+YOU.,;",+100),+'m'+-+'u');
++++EXPECT_EQUALS(strncmp(++"nice+to+meet+you.,;",+"nice+to+uEET+YOU.,;",+100),+'m'+-+'u');
++++EXPECT_EQUALS(strncmp(++"nice+to+meet+you.,;",+"nice+to+UEET+YOU.,;",+100),+'m'+-+'U');

++++EXPECT_EQUALS(strncmpci("nice+to+meet+you.,;",+"NICE+TO+MEET+YOU.,;",+5),+0);
++++EXPECT_EQUALS(strncmp(++"nice+to+meet+you.,;",+"NICE+TO+MEET+YOU.,;",+5),+'n'+-+'N');

++++EXPECT_EQUALS(strncmpci("nice+to+meet+you.,;",+"NICE+eo+UEET+YOU.,;",+5),+0);
++++EXPECT_EQUALS(strncmp(++"nice+to+meet+you.,;",+"nice+eo+uEET+YOU.,;",+5),+0);

++++EXPECT_EQUALS(strncmpci("nice+to+meet+you.,;",+"NICE+eo+UEET+YOU.,;",+100),+'t'+-+'e');
++++EXPECT_EQUALS(strncmp(++"nice+to+meet+you.,;",+"nice+eo+uEET+YOU.,;",+100),+'t'+-+'e');

++++EXPECT_EQUALS(strncmpci("nice+to+meet+you.,;",+"nice-eo+UEET+YOU.,;",+5),+'+'+-+'-');
++++EXPECT_EQUALS(strncmp(++"nice+to+meet+you.,;",+"nice-eo+UEET+YOU.,;",+5),+'+'+-+'-');


++++if+(globals.error_count+==+num_failures_expected)
++++{
++++++++printf(ANSI_COLOR_GRN+"All+unit+tests+passed!"+ANSI_COLOR_OFF+"\n");
++++}
++++else
++++{
++++++++printf(ANSI_COLOR_RED+"FAILED+UNIT+TESTS!+NUMBER+OF+UNEXPECTED+FAILURES+=+%25i"
++++++++++++ANSI_COLOR_OFF+"\n",+globals.error_count+-+num_failures_expected);
++++}

++++assert(globals.error_count+==+num_failures_expected);
++++return+globals.error_count;
}|1501482|示例输出：|1501483|1501484|+$+-Wall+-Wextra+-Werror+-ggdb+-std=c11+-o+./bin/tmp+strncmpci.c+&&+./bin/tmp在函数main的第250行失败！strncmpci(“嘿”，“嘿”，3)+!=+'H‘-+'h’a:+strncmpci(“嘿”，“嘿”，3)+is+0+b：'H‘-+'h’is+32+-开始-所有单元测试通过！|blockquote|1501485|1501486|1501487|参考文献：|1501488|这个问题和这里的其他答案给了我灵感，并给出了一些洞察力和行为研究，我做了一些研究来修复上面的部分代码(参见下面的评论)：|1501489|Google+search+|1501490|+"c+undefined+behavior+reading+outside+array+bounds"|1501491|Is+accessing+a+global+array+outside+its+bound+undefined+behavior?|1501492|https://en.cppreference.com/w/cpp/language/ub+-也可以看到底部的许多非常棒的“外部链接”！|1501493|1/3：http://blog.llvm.org/2011/05/what-every-c-programmer-should-know.html|1501494|2/3：https://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html|1501495|3/3：https://blog.llvm.org/2011/05/what-every-c-programmer-should-know_21.html|1501496|https://blog.regehr.org/archives/213|1501497|https://www.geeksforgeeks.org/accessing-array-bounds-ccpp/|1501498|1501499|需要进一步研究的课题|1501500|1501501|(注意:这是C%2B%2B，不是C)+OnlineGDB上的Lowercase+of+Unicode+character|1501502|tolower_tests.c：https://onlinegdb.com/HyZieXcew|1501503|1501504|TODO：|1501505|1501506|制作此代码的一个版本，它也适用于Unicode的UTF-8实现(字符编码)！|1501507|1501508|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/5820991/4561887|1|http://www.cplusplus.com/reference/cstring/strncmp/|2|https://github.com/ElectricRCAircraftGuy/eRCaGuy_hello_world|3|https://github.com/ElectricRCAircraftGuy/eRCaGuy_hello_world/blob/master/c/strncmpci.c|4|https://www.google.com/search?q=c%2Bundefined%2Bbehavior%2Breading%2Boutside%2Barray%2Bbounds&oq=c%2Bundefined%2Bbehavior%2Breading%2Boutside%2Barray%2Bbounds&aqs=chrome..69i57j69i64l3.10484j0j7&sourceid=chrome&ie=UTF-8|5|https://stackoverflow.com/questions/26426910/is-accessing-a-global-array-outside-its-bound-undefined-behavior|6|https://en.cppreference.com/w/cpp/language/ub|7|http://blog.llvm.org/2011/05/what-every-c-programmer-should-know.html|8|https://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html|9|https://blog.llvm.org/2011/05/what-every-c-programmer-should-know_21.html|10|11|12|https://stackoverflow.com/questions/34433380/lowercase-of-unicode-character|13|https://onlinegdb.com/HyZieXcew|14|https://en.wikipedia.org/wiki/UTF-8^0|2I|8|4|O|0|0|3|9|3|9|1|0|2|9|0|0|0|1C|9|28|4|2I|7|0|0|0|0|3|B|0|0|0|6|0|0|0|3|J|2|16|C|3|0|0|0|0|0|0|0|0|0|0|0|1|1F|4|0|0|1T|5|0|0|19|6|0|4|1X|7|0|4|21|8|0|4|21|9|0|0|10|A|0|0|1M|B|0|0|0|0|Q|U|C|0|0|F|G|V|D|0|0|0|0|O|5|E|0|0^^$0|@$1|2|3|4|5|6|7|3M|8|@$9|3N|A|3O|B|C]]|D|@$9|3P|A|3Q|1|3R]]|E|$]]|$1|F|3|G|5|6|7|3S|8|@$9|3T|A|3U|B|C]]|D|@$9|3V|A|3W|1|3X]]|E|$]]|$1|H|3|I|5|6|7|3Y|8|@$9|3Z|A|40|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|41|8|@]|D|@]|E|$]]|$1|L|3|M|5|N|7|42|8|@]|D|@]|E|$]]|$1|O|3|P|5|Q|7|43|8|@$9|44|A|45|B|C]|$9|46|A|47|B|C]|$9|48|A|49|B|C]]|D|@]|E|$]]|$1|R|3|-4|5|6|7|4A|8|@]|D|@]|E|$]]|$1|S|3|-4|5|6|7|4B|8|@]|D|@]|E|$]]|$1|T|3|U|5|6|7|4C|8|@]|D|@]|E|$]]|$1|V|3|W|5|6|7|4D|8|@$9|4E|A|4F|B|X]]|D|@]|E|$]]|$1|Y|3|Z|5|10|7|4G|8|@]|D|@]|E|$11|12]]|$1|13|3|14|5|6|7|4H|8|@$9|4I|A|4J|B|X]]|D|@]|E|$]]|$1|15|3|16|5|10|7|4K|8|@]|D|@]|E|$11|12]]|$1|17|3|18|5|6|7|4L|8|@]|D|@]|E|$]]|$1|19|3|1A|5|6|7|4M|8|@]|D|@$9|4N|A|4O|1|4P]|$9|4Q|A|4R|1|4S]]|E|$]]|$1|1B|3|1C|5|6|7|4T|8|@]|D|@]|E|$]]|$1|1D|3|1E|5|10|7|4U|8|@]|D|@]|E|$11|12]]|$1|1F|3|1G|5|6|7|4V|8|@]|D|@]|E|$]]|$1|1H|3|-4|5|6|7|4W|8|@]|D|@]|E|$]]|$1|1I|3|1J|5|1K|7|4X|8|@]|D|@]|E|$]]|$1|1L|3|-4|5|6|7|4Y|8|@]|D|@]|E|$]]|$1|1M|3|-4|5|6|7|4Z|8|@]|D|@]|E|$]]|$1|1N|3|1O|5|6|7|50|8|@]|D|@]|E|$]]|$1|1P|3|1Q|5|6|7|51|8|@]|D|@]|E|$]]|$1|1R|3|1S|5|Q|7|52|8|@]|D|@]|E|$]]|$1|1T|3|1U|5|Q|7|53|8|@]|D|@$9|54|A|55|1|56]]|E|$]]|$1|1V|3|1W|5|Q|7|57|8|@]|D|@$9|58|A|59|1|5A]]|E|$]]|$1|1X|3|1Y|5|Q|7|5B|8|@]|D|@$9|5C|A|5D|1|5E]]|E|$]]|$1|1Z|3|20|5|Q|7|5F|8|@]|D|@$9|5G|A|5H|1|5I]]|E|$]]|$1|21|3|22|5|Q|7|5J|8|@]|D|@$9|5K|A|5L|1|5M]]|E|$]]|$1|23|3|24|5|Q|7|5N|8|@]|D|@$9|5O|A|5P|1|5Q]]|E|$]]|$1|25|3|26|5|Q|7|5R|8|@]|D|@$9|5S|A|5T|1|5U]]|E|$]]|$1|27|3|28|5|Q|7|5V|8|@]|D|@$9|5W|A|5X|1|5Y]]|E|$]]|$1|29|3|-4|5|6|7|5Z|8|@]|D|@]|E|$]]|$1|2A|3|2B|5|6|7|60|8|@]|D|@]|E|$]]|$1|2C|3|-4|5|6|7|61|8|@]|D|@]|E|$]]|$1|2D|3|2E|5|Q|7|62|8|@]|D|@$9|63|A|64|1|65]]|E|$]]|$1|2F|3|2G|5|Q|7|66|8|@$9|67|A|68|B|X]]|D|@$9|69|A|6A|1|6B]]|E|$]]|$1|2H|3|-4|5|6|7|6C|8|@]|D|@]|E|$]]|$1|2I|3|2J|5|6|7|6D|8|@]|D|@]|E|$]]|$1|2K|3|-4|5|6|7|6E|8|@]|D|@]|E|$]]|$1|2L|3|2M|5|Q|7|6F|8|@]|D|@$9|6G|A|6H|1|6I]]|E|$]]|$1|2N|3|-4|5|6|7|6J|8|@]|D|@]|E|$]]|$1|2O|3|-4|5|6|7|6K|8|@]|D|@]|E|$]]]|2P|$2Q|$5|2R|2S|2T|E|$2U|2V]]|2W|$5|2R|2S|2T|E|$2U|2X]]|2Y|$5|2R|2S|2T|E|$2U|2Z]]|30|$5|2R|2S|2T|E|$2U|31]]|32|$5|2R|2S|2T|E|$2U|33]]|34|$5|2R|2S|2T|E|$2U|35]]|36|$5|2R|2S|2T|E|$2U|37]]|38|$5|2R|2S|2T|E|$2U|39]]|3A|$5|2R|2S|2T|E|$2U|3B]]|3C|$5|2R|2S|2T|E|$2U|3D]]|3E|$5|2R|2S|2T|E|$2U|26]]|3F|$5|2R|2S|2T|E|$2U|28]]|3G|$5|2R|2S|2T|E|$2U|3H]]|3I|$5|2R|2S|2T|E|$2U|3J]]|3K|$5|2R|2S|2T|E|$2U|3L]]]]

I'm not really a fan of the <a href="https://stackoverflow.com/a/5820991/4561887">most-upvoted answer here</a> (in part because it seems like it isn't correct since it should <code>continue</code> if it reads a null terminator in either string--but not both strings at once--and it doesn't do this), so I wrote my own.
<h2>This is a direct drop-in replacement for <a href="http://www.cplusplus.com/reference/cstring/strncmp/" rel="nofollow noreferrer"><code>strncmp()</code></a>, and has been tested with numerous test cases, as shown below.</h2>
It is identical to <code>strncmp()</code> except:
<ol>
<li>It is case-insensitive.</li>
<li>The behavior is NOT undefined (it is well-defined) if either string is a null ptr. Regular <code>strncmp()</code> has undefined behavior if either string is a null ptr (see: <a href="https://en.cppreference.com/w/cpp/string/byte/strncmp" rel="nofollow noreferrer">https://en.cppreference.com/w/cpp/string/byte/strncmp</a>).</li>
<li>It returns <code>INT_MIN</code> as a special sentinel error value if either input string is a <code>NULL</code> ptr.</li>
</ol>
LIMITATIONS: Note that this code works on the original <a href="https://en.wikipedia.org/wiki/ASCII#Printable_characters" rel="nofollow noreferrer">7-bit ASCII character set only</a> (decimal values 0 to 127, inclusive), NOT on <a href="https://en.wikipedia.org/wiki/Unicode" rel="nofollow noreferrer">unicode</a> characters, such as unicode character encodings <a href="https://en.wikipedia.org/wiki/UTF-8" rel="nofollow noreferrer">UTF-8</a> (the most popular), <a href="https://en.wikipedia.org/wiki/UTF-16" rel="nofollow noreferrer">UTF-16</a>, and <a href="https://en.wikipedia.org/wiki/UTF-32" rel="nofollow noreferrer">UTF-32</a>.
Here is the code only (no comments):
<pre><code>int strncmpci(const char * str1, const char * str2, size_t num)
{
 int ret_code = 0;
 size_t chars_compared = 0;

 if (!str1 || !str2)
 {
 ret_code = INT_MIN;
 return ret_code;
 }

 while ((chars_compared &lt; num) &amp;&amp; (*str1 || *str2))
 {
 ret_code = tolower((int)(*str1)) - tolower((int)(*str2));
 if (ret_code != 0)
 {
 break;
 }
 chars_compared++;
 str1++;
 str2++;
 }

 return ret_code;
}
</code></pre>
Fully-commented version:
<pre><code>/// \brief Perform a case-insensitive string compare (`strncmp()` case-insensitive) to see
/// if two C-strings are equal.
/// \note 1. Identical to `strncmp()` except:
/// 1. It is case-insensitive.
/// 2. The behavior is NOT undefined (it is well-defined) if either string is a null
/// ptr. Regular `strncmp()` has undefined behavior if either string is a null ptr
/// (see: https://en.cppreference.com/w/cpp/string/byte/strncmp).
/// 3. It returns `INT_MIN` as a special sentinel value for certain errors.
/// - Posted as an answer here: https://stackoverflow.com/a/55293507/4561887.
/// - Aided/inspired, in part, by `strcicmp()` here:
/// https://stackoverflow.com/a/5820991/4561887.
/// \param[in] str1 C string 1 to be compared.
/// \param[in] str2 C string 2 to be compared.
/// \param[in] num max number of chars to compare
/// \return A comparison code (identical to `strncmp()`, except with the addition
/// of `INT_MIN` as a special sentinel value):
///
/// INT_MIN (usually -2147483648 for int32_t integers) Invalid arguments (one or both
/// of the input strings is a NULL pointer).
/// &lt;0 The first character that does not match has a lower value in str1 than
/// in str2.
/// 0 The contents of both strings are equal.
/// &gt;0 The first character that does not match has a greater value in str1 than
/// in str2.
int strncmpci(const char * str1, const char * str2, size_t num)
{
 int ret_code = 0;
 size_t chars_compared = 0;

 // Check for NULL pointers
 if (!str1 || !str2)
 {
 ret_code = INT_MIN;
 return ret_code;
 }

 // Continue doing case-insensitive comparisons, one-character-at-a-time, of `str1` to `str2`, so
 // long as 1st: we have not yet compared the requested number of chars, and 2nd: the next char
 // of at least *one* of the strings is not zero (the null terminator for a C-string), meaning
 // that string still has more characters in it.
 // Note: you MUST check `(chars_compared &lt; num)` FIRST or else dereferencing (reading) `str1` or
 // `str2` via `*str1` and `*str2`, respectively, is undefined behavior if you are reading one or
 // both of these C-strings outside of their array bounds.
 while ((chars_compared &lt; num) &amp;&amp; (*str1 || *str2))
 {
 ret_code = tolower((int)(*str1)) - tolower((int)(*str2));
 if (ret_code != 0)
 {
 // The 2 chars just compared don't match
 break;
 }
 chars_compared++;
 str1++;
 str2++;
 }

 return ret_code;
}
</code></pre>
<h2>Test code:</h2>
Download the entire sample code, with unit tests, from my <a href="https://github.com/ElectricRCAircraftGuy/eRCaGuy_hello_world" rel="nofollow noreferrer">eRCaGuy_hello_world</a> repository here: &quot;<a href="https://github.com/ElectricRCAircraftGuy/eRCaGuy_hello_world/blob/master/c/strncmpci.c" rel="nofollow noreferrer">strncmpci.c&quot;</a>:
(this is just a snippet)
<pre><code>int main()
{
 printf(&quot;-----------------------\n&quot;
 &quot;String Comparison Tests\n&quot;
 &quot;-----------------------\n\n&quot;);

 int num_failures_expected = 0;

 printf(&quot;INTENTIONAL UNIT TEST FAILURE to show what a unit test failure looks like!\n&quot;);
 EXPECT_EQUALS(strncmpci(&quot;hey&quot;, &quot;HEY&quot;, 3), 'h' - 'H');
 num_failures_expected++;
 printf(&quot;------ beginning ------\n\n&quot;);


 const char * str1;
 const char * str2;
 size_t n;

 // NULL ptr checks
 EXPECT_EQUALS(strncmpci(NULL, &quot;&quot;, 0), INT_MIN);
 EXPECT_EQUALS(strncmpci(&quot;&quot;, NULL, 0), INT_MIN);
 EXPECT_EQUALS(strncmpci(NULL, NULL, 0), INT_MIN);
 EXPECT_EQUALS(strncmpci(NULL, &quot;&quot;, 10), INT_MIN);
 EXPECT_EQUALS(strncmpci(&quot;&quot;, NULL, 10), INT_MIN);
 EXPECT_EQUALS(strncmpci(NULL, NULL, 10), INT_MIN);

 EXPECT_EQUALS(strncmpci(&quot;&quot;, &quot;&quot;, 0), 0);
 EXPECT_EQUALS(strncmp(&quot;&quot;, &quot;&quot;, 0), 0);

 str1 = &quot;&quot;;
 str2 = &quot;&quot;;
 n = 0;
 EXPECT_EQUALS(strncmpci(str1, str2, n), 0);
 EXPECT_EQUALS(strncmp(str1, str2, n), 0);

 str1 = &quot;hey&quot;;
 str2 = &quot;HEY&quot;;
 n = 0;
 EXPECT_EQUALS(strncmpci(str1, str2, n), 0);
 EXPECT_EQUALS(strncmp(str1, str2, n), 0);

 str1 = &quot;hey&quot;;
 str2 = &quot;HEY&quot;;
 n = 3;
 EXPECT_EQUALS(strncmpci(str1, str2, n), 0);
 EXPECT_EQUALS(strncmp(str1, str2, n), 'h' - 'H');

 str1 = &quot;heY&quot;;
 str2 = &quot;HeY&quot;;
 n = 3;
 EXPECT_EQUALS(strncmpci(str1, str2, n), 0);
 EXPECT_EQUALS(strncmp(str1, str2, n), 'h' - 'H');

 str1 = &quot;hey&quot;;
 str2 = &quot;HEdY&quot;;
 n = 3;
 EXPECT_EQUALS(strncmpci(str1, str2, n), 'y' - 'd');
 EXPECT_EQUALS(strncmp(str1, str2, n), 'h' - 'H');

 str1 = &quot;heY&quot;;
 str2 = &quot;hEYd&quot;;
 n = 3;
 EXPECT_EQUALS(strncmpci(str1, str2, n), 0);
 EXPECT_EQUALS(strncmp(str1, str2, n), 'e' - 'E');

 str1 = &quot;heY&quot;;
 str2 = &quot;heyd&quot;;
 n = 6;
 EXPECT_EQUALS(strncmpci(str1, str2, n), -'d');
 EXPECT_EQUALS(strncmp(str1, str2, n), 'Y' - 'y');

 str1 = &quot;hey&quot;;
 str2 = &quot;hey&quot;;
 n = 6;
 EXPECT_EQUALS(strncmpci(str1, str2, n), 0);
 EXPECT_EQUALS(strncmp(str1, str2, n), 0);

 str1 = &quot;hey&quot;;
 str2 = &quot;heyd&quot;;
 n = 6;
 EXPECT_EQUALS(strncmpci(str1, str2, n), -'d');
 EXPECT_EQUALS(strncmp(str1, str2, n), -'d');

 str1 = &quot;hey&quot;;
 str2 = &quot;heyd&quot;;
 n = 3;
 EXPECT_EQUALS(strncmpci(str1, str2, n), 0);
 EXPECT_EQUALS(strncmp(str1, str2, n), 0);

 str1 = &quot;hEY&quot;;
 str2 = &quot;heyYOU&quot;;
 n = 3;
 EXPECT_EQUALS(strncmpci(str1, str2, n), 0);
 EXPECT_EQUALS(strncmp(str1, str2, n), 'E' - 'e');

 str1 = &quot;hEY&quot;;
 str2 = &quot;heyYOU&quot;;
 n = 10;
 EXPECT_EQUALS(strncmpci(str1, str2, n), -'y');
 EXPECT_EQUALS(strncmp(str1, str2, n), 'E' - 'e');

 str1 = &quot;hEYHowAre&quot;;
 str2 = &quot;heyYOU&quot;;
 n = 10;
 EXPECT_EQUALS(strncmpci(str1, str2, n), 'h' - 'y');
 EXPECT_EQUALS(strncmp(str1, str2, n), 'E' - 'e');

 EXPECT_EQUALS(strncmpci(&quot;nice to meet you.,;&quot;, &quot;NICE TO MEET YOU.,;&quot;, 100), 0);
 EXPECT_EQUALS(strncmp( &quot;nice to meet you.,;&quot;, &quot;NICE TO MEET YOU.,;&quot;, 100), 'n' - 'N');
 EXPECT_EQUALS(strncmp( &quot;nice to meet you.,;&quot;, &quot;nice to meet you.,;&quot;, 100), 0);

 EXPECT_EQUALS(strncmpci(&quot;nice to meet you.,;&quot;, &quot;NICE TO UEET YOU.,;&quot;, 100), 'm' - 'u');
 EXPECT_EQUALS(strncmp( &quot;nice to meet you.,;&quot;, &quot;nice to uEET YOU.,;&quot;, 100), 'm' - 'u');
 EXPECT_EQUALS(strncmp( &quot;nice to meet you.,;&quot;, &quot;nice to UEET YOU.,;&quot;, 100), 'm' - 'U');

 EXPECT_EQUALS(strncmpci(&quot;nice to meet you.,;&quot;, &quot;NICE TO MEET YOU.,;&quot;, 5), 0);
 EXPECT_EQUALS(strncmp( &quot;nice to meet you.,;&quot;, &quot;NICE TO MEET YOU.,;&quot;, 5), 'n' - 'N');

 EXPECT_EQUALS(strncmpci(&quot;nice to meet you.,;&quot;, &quot;NICE eo UEET YOU.,;&quot;, 5), 0);
 EXPECT_EQUALS(strncmp( &quot;nice to meet you.,;&quot;, &quot;nice eo uEET YOU.,;&quot;, 5), 0);

 EXPECT_EQUALS(strncmpci(&quot;nice to meet you.,;&quot;, &quot;NICE eo UEET YOU.,;&quot;, 100), 't' - 'e');
 EXPECT_EQUALS(strncmp( &quot;nice to meet you.,;&quot;, &quot;nice eo uEET YOU.,;&quot;, 100), 't' - 'e');

 EXPECT_EQUALS(strncmpci(&quot;nice to meet you.,;&quot;, &quot;nice-eo UEET YOU.,;&quot;, 5), ' ' - '-');
 EXPECT_EQUALS(strncmp( &quot;nice to meet you.,;&quot;, &quot;nice-eo UEET YOU.,;&quot;, 5), ' ' - '-');


 if (globals.error_count == num_failures_expected)
 {
 printf(ANSI_COLOR_GRN &quot;All unit tests passed!&quot; ANSI_COLOR_OFF &quot;\n&quot;);
 }
 else
 {
 printf(ANSI_COLOR_RED &quot;FAILED UNIT TESTS! NUMBER OF UNEXPECTED FAILURES = %i&quot;
 ANSI_COLOR_OFF &quot;\n&quot;, globals.error_count - num_failures_expected);
 }

 assert(globals.error_count == num_failures_expected);
 return globals.error_count;
}
</code></pre>
<h2>Sample output:</h2>
<blockquote>
<pre><code>$ gcc -Wall -Wextra -Werror -ggdb -std=c11 -o ./bin/tmp strncmpci.c &amp;&amp; ./bin/tmp
-----------------------
String Comparison Tests
-----------------------

INTENTIONAL UNIT TEST FAILURE to show what a unit test failure looks like!
FAILED at line 250 in function main! strncmpci(&quot;hey&quot;, &quot;HEY&quot;, 3) != 'h' - 'H'
 a: strncmpci(&quot;hey&quot;, &quot;HEY&quot;, 3) is 0
 b: 'h' - 'H' is 32

------ beginning ------

All unit tests passed!
</code></pre>
</blockquote>
<h2>References:</h2>
<ol>
<li>This question &amp; other answers here served as inspiration and gave some insight (<a href="https://stackoverflow.com/questions/5820810/case-insensitive-string-comp-in-c/">Case Insensitive String comp in C</a>)</li>
<li><a href="http://www.cplusplus.com/reference/cstring/strncmp/" rel="nofollow noreferrer">http://www.cplusplus.com/reference/cstring/strncmp/</a></li>
<li><a href="https://en.wikipedia.org/wiki/ASCII" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/ASCII</a></li>
<li><a href="https://en.cppreference.com/w/c/language/operator_precedence" rel="nofollow noreferrer">https://en.cppreference.com/w/c/language/operator_precedence</a></li>
<li>Undefined Behavior research I did to fix part of my code above (see comments below):
<ol>
<li>Google search for <a href="https://www.google.com/search?q=c+undefined+behavior+reading+outside+array+bounds&amp;oq=c+undefined+behavior+reading+outside+array+bounds&amp;aqs=chrome..69i57j69i64l3.10484j0j7&amp;sourceid=chrome&amp;ie=UTF-8" rel="nofollow noreferrer">&quot;c undefined behavior reading outside array bounds&quot;</a></li>
<li><a href="https://stackoverflow.com/questions/26426910/is-accessing-a-global-array-outside-its-bound-undefined-behavior">Is accessing a global array outside its bound undefined behavior?</a></li>
<li><a href="https://en.cppreference.com/w/cpp/language/ub" rel="nofollow noreferrer">https://en.cppreference.com/w/cpp/language/ub</a> - see also the many really great &quot;External links&quot; at the bottom!</li>
<li>1/3: <a href="http://blog.llvm.org/2011/05/what-every-c-programmer-should-know.html" rel="nofollow noreferrer">http://blog.llvm.org/2011/05/what-every-c-programmer-should-know.html</a></li>
<li>2/3: <a href="https://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html" rel="nofollow noreferrer">https://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html</a></li>
<li>3/3: <a href="https://blog.llvm.org/2011/05/what-every-c-programmer-should-know_21.html" rel="nofollow noreferrer">https://blog.llvm.org/2011/05/what-every-c-programmer-should-know_21.html</a></li>
<li><a href="https://blog.regehr.org/archives/213" rel="nofollow noreferrer">https://blog.regehr.org/archives/213</a></li>
<li><a href="https://www.geeksforgeeks.org/accessing-array-bounds-ccpp/" rel="nofollow noreferrer">https://www.geeksforgeeks.org/accessing-array-bounds-ccpp/</a></li>
</ol>
</li>
</ol>
<h2>Topics to further research</h2>
<ol>
<li>(Note: this is C++, not C) <a href="https://stackoverflow.com/questions/34433380/lowercase-of-unicode-character">Lowercase of Unicode character</a></li>
<li>tolower_tests.c on OnlineGDB: <a href="https://onlinegdb.com/HyZieXcew" rel="nofollow noreferrer">https://onlinegdb.com/HyZieXcew</a></li>
</ol>
<h2>TODO:</h2>
<ol>
<li>Make a version of this code which also works on Unicode's <a href="https://en.wikipedia.org/wiki/UTF-8" rel="nofollow noreferrer">UTF-8</a> implementation (character encoding)!</li>
</ol>

blocks|key|3877002|text|正如其他人所说，没有可移植的功能可以在所有系统上工作。您可以使用简单的ifdef部分地绕过这一点|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3877003|#include+<stdio.h>

#ifdef+_WIN32
#include+<string.h>
#define+strcasecmp+_stricmp
#else+//+assuming+POSIX+or+BSD+compliant+system
#include+<strings.h>
#endif

int+main()+{
++++printf("%25d",+strcasecmp("teSt",+"TEst"));
}|code-block|syntax|javascript|3877004|entityMap^0|Z|5|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

As others have stated, there is no portable function that works on all systems. You can partially circumvent this with simple <code>ifdef</code>:

<pre><code>#include &lt;stdio.h&gt;

#ifdef _WIN32
#include &lt;string.h&gt;
#define strcasecmp _stricmp
#else // assuming POSIX or BSD compliant system
#include &lt;strings.h&gt;
#endif

int main() {
 printf("%d", strcasecmp("teSt", "TEst"));
}
</code></pre>

blocks|key|5293891|text|如果库中没有，你可以从here得到一个想法，如何实现一个有效的想法|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|5293892|它使用一个表来存储全部256个字符。|5293893|该表中除字母外的所有字符都使用其ascii代码。|5293894|。用于大写字母代码的|unordered-list-item|5293895|-该表列出了小写符号的代码。|5293896|5293897|然后，我们只需要遍历一个字符串并比较给定字符的表格单元格：|5293898|const+char+*cm+=+charmap,
++++++++*us1+=+(const+char+*)s1,
++++++++*us2+=+(const+char+*)s2;
while+(cm[*us1]+==+cm[*us2%2B%2B])
++++if+(*us1%2B%2B+==+'\0')
++++++++return+(0);
return+(cm[*us1]+-+cm[*--us2]);|code-block|syntax|javascript|5293899|entityMap|0|LINK|mutability|MUTABLE|url|http://www.opensource.apple.com/source/Libc/Libc-167/string.subproj/strcasecmp.c^0|B|4|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@$A|13|B|14|1|15]]|C|$]]|$1|D|3|E|5|6|7|16|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|17|8|@]|9|@]|C|$]]|$1|H|3|I|5|J|7|18|8|@]|9|@]|C|$]]|$1|K|3|L|5|J|7|19|8|@]|9|@]|C|$]]|$1|M|3|-4|5|6|7|1A|8|@]|9|@]|C|$]]|$1|N|3|O|5|6|7|1B|8|@]|9|@]|C|$]]|$1|P|3|Q|5|R|7|1C|8|@]|9|@]|C|$S|T]]|$1|U|3|-4|5|6|7|1D|8|@]|9|@]|C|$]]]|V|$W|$5|X|Y|Z|C|$10|11]]]]

You can get an idea, how to implement an efficient one, if you don't have any in the library, from <a href="http://www.opensource.apple.com/source/Libc/Libc-167/string.subproj/strcasecmp.c" rel="nofollow">here</a>

It use a table for all 256 chars. 

<ul>
<li>in that table for all chars, except letters - used its ascii codes. </li>
<li>for upper case letter codes - the table list codes of lower cased symbols. </li>
</ul>

then we just need to traverse a strings and compare our table cells for a given chars:

<pre><code>const char *cm = charmap,
 *us1 = (const char *)s1,
 *us2 = (const char *)s2;
while (cm[*us1] == cm[*us2++])
 if (*us1++ == '\0')
 return (0);
return (cm[*us1] - cm[*--us2]);
</code></pre>

blocks|key|3877019|text|简单的解决方案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3877020|int+str_case_ins_cmp(const+char*+a,+const+char*+b)+{
++int+rc;

++while+(1)+{
++++rc+=+tolower((unsigned+char)*a)+-+tolower((unsigned+char)*b);
++++if+(rc+%7C%7C+!*a)+{
++++++break;
++++}

++++%2B%2Ba;
++++%2B%2Bb;
++}

++return+rc;
}|code-block|syntax|javascript|3877021|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Simple solution:

<pre><code>int str_case_ins_cmp(const char* a, const char* b) {
 int rc;

 while (1) {
 rc = tolower((unsigned char)*a) - tolower((unsigned char)*b);
 if (rc || !*a) {
 break;
 }

 ++a;
 ++b;
 }

 return rc;
}
</code></pre>

blocks|key|1501412|text|static+int+ignoreCaseComp+(const+char+*str1,+const+char+*str2,+int+length)
{
++++int+k;
++++for+(k+=+0;+k+<+length;+k%2B%2B)
++++{

++++++++if+((str1[k]+%7C+32)+!=+(str2[k]+%7C+32))
++++++++++++break;
++++}

++++if+(k+!=+length)
++++++++return+1;
++++return+0;
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1501413|Reference|unstyled|offset|length|1501414|entityMap|0|LINK|mutability|MUTABLE|url|https://chromium.googlesource.com/external/liblouis/%2B/master/liblouis/wrappers.c^0|0|0|9|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|R|8|@]|9|@$G|S|H|T|1|U]]|A|$]]|$1|I|3|-4|5|F|7|V|8|@]|9|@]|A|$]]]|J|$K|$5|L|M|N|A|$O|P]]]]

<pre><code>static int ignoreCaseComp (const char *str1, const char *str2, int length)
{
 int k;
 for (k = 0; k &lt; length; k++)
 {

 if ((str1[k] | 32) != (str2[k] | 32))
 break;
 }

 if (k != length)
 return 1;
 return 0;
}
</code></pre>

<a href="https://chromium.googlesource.com/external/liblouis/+/master/liblouis/wrappers.c" rel="nofollow">Reference</a>

blocks|key|1766482|text|如果我们有一个null结尾的字符：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1766483|+++bool+striseq(const+char*+s1,const+char*+s2){+
+++++for(;*s1;){+
+++++++if(tolower(*s1%2B%2B)!=tolower(*s2%2B%2B))+
+++++++++return+false;+
++++++}+
++++++return+*s1+==+*s2;
++++}|code-block|syntax|javascript|1766484|或者使用这个使用位运算的版本：|1766485|++++int+striseq(const+char*+s1,const+char*+s2)
+++++++{for(;*s1;)+if((*s1%2B%2B%7C32)!=(*s2%2B%2B%7C32))+return+0;+return+*s1+==+*s2;}|1766486|我不确定这是否适用于符号，我还没有在那里测试过，但对字母很有效。|1766487|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

if we have a null terminated character:
<pre><code> bool striseq(const char* s1,const char* s2){ 
 for(;*s1;){ 
 if(tolower(*s1++)!=tolower(*s2++)) 
 return false; 
 } 
 return *s1 == *s2;
 }

</code></pre>
or with this version that uses bitwise operations:
<pre><code> int striseq(const char* s1,const char* s2)
 {for(;*s1;) if((*s1++|32)!=(*s2++|32)) return 0; return *s1 == *s2;}

</code></pre>
i'm not sure if this works with symbols, I haven't tested there, but works fine with letters.

blocks|key|1766288|text|int+strcmpInsensitive(char*+a,+char*+b)
{
++++return+strcmp(lowerCaseWord(a),+lowerCaseWord(b));
}

char*+lowerCaseWord(char*+a)
{
++++char+*b=new+char[strlen(a)];
++++for+(int+i+=+0;+i+<+strlen(a);+i%2B%2B)
++++{
++++++++b[i]+=+tolower(a[i]);+++
++++}
++++return+b;
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1766289|祝好运|unstyled|1766290|Edit-lowerCaseWord函数使用获取一个char*变量，并返回该char*的小写数值。例如，"abcde“表示字符*的值，将返回"AbCdE”。|1766291|基本上，它所做的是将两个char*变量转换为小写后，并对其使用strcmp函数。|1766292|例如，如果我们为"AbCdE“和"ABCDE”的值调用strcmp函数，它将首先返回两个小写的值("abcde")，然后对它们执行strcmp函数。|1766293|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|P|8|@]|9|@]|A|$]]|$1|G|3|H|5|F|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|F|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|F|7|T|8|@]|9|@]|A|$]]]|N|$]]

<pre><code>int strcmpInsensitive(char* a, char* b)
{
 return strcmp(lowerCaseWord(a), lowerCaseWord(b));
}

char* lowerCaseWord(char* a)
{
 char *b=new char[strlen(a)];
 for (int i = 0; i &lt; strlen(a); i++)
 {
 b[i] = tolower(a[i]); 
 }
 return b;
}
</code></pre>

good luck

Edit-lowerCaseWord function get a char* variable with, and return the lower case value of this char*. For example "AbCdE" for value of char*, will return "abcde".

Basically what it does is to take the two char* variables, after being transferred to lower case, and make use the strcmp function on them.

For example- if we call the strcmpInsensitive function for values of "AbCdE", and "ABCDE", it will first return both values in lower case ("abcde"), and then do strcmp function on them.

I have two postcodes <code>char*</code> that I want to compare, ignoring case.
Is there a function to do this?
Or do I have to loop through each use the <code>tolower</code> function and then do the comparison?
Any idea how this function will react with numbers in the string
Thanks

Case Insensitive String Comparison in C

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有两个邮政编码char*，我想要比较，忽略大小写。有没有一个函数可以做到这一点？或者我必须遍历每个use tolower函数，然后进行比较？你知道这个函数将如何处理字符串中的数字吗？谢谢

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