blocks|key|1273956|text|您只是在处理ASCII字符串，并且没有区域设置问题吗？那么，是的，这将是一个很好的方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1273957|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Are you just dealing with ASCII strings, and have no locale issues? Then yes, that would be a good way to do it.

blocks|key|1059261|text|它在标准库中，这是我所能看到的实现这样一个函数的最直接的方法。所以是的，只需遍历字符串并将每个字符转换为小写。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1059262|像这样微不足道的东西：|1059263|#include+<ctype.h>

for(int+i+=+0;+str[i];+i%2B%2B){
++str[i]+=+tolower(str[i]);
}|code-block|syntax|javascript|1059264|或者如果你更喜欢一种衬垫，那么你可以使用J.F.+Sebastian的这一种：|1059265|for+(+;+*p;+%2B%2Bp)+*p+=+tolower(*p);|1059266|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|$]]

It's in the standard library, and that's the most straight forward way I can see to implement such a function. So yes, just loop through the string and convert each character to lowercase. 

Something trivial like this:

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

for(int i = 0; str[i]; i++){
 str[i] = tolower(str[i]);
}
</code></pre>

or if you prefer one liners, then you can use this one by J.F. Sebastian:

<pre><code>for ( ; *p; ++p) *p = tolower(*p);
</code></pre>

blocks|key|1059317|text|如果您将自己限制为ASCII，则转换为小写相当于上升位0x60：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1059318|for(char+*p+=+pstr;+*p;+%2B%2Bp)
++++*p+=+*p+>+0x40+&&+*p+<+0x5b+?+*p+%7C+0x60+:+*p;|code-block|syntax|javascript|1059319|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|$]]

to convert to lower case is equivalent to rise bit 0x60 if you restrict yourself to ASCII:
<pre><code>for(char *p = pstr; *p; ++p)
 *p = *p &gt; 0x40 &amp;&amp; *p &lt; 0x5b ? *p | 0x60 : *p;
</code></pre>

blocks|key|1059364|text|如果您需要小写函数中的Unicode支持，请参阅此问题：Light+C+Unicode+Library|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1059365|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/313555/light-c-unicode-library^0|S|N|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

If you need Unicode support in the lower case function see this question:
<a href="https://stackoverflow.com/questions/313555/light-c-unicode-library">Light C Unicode Library</a>

blocks|key|1274139|text|如果我们要草率地使用tolower()，可以这样做：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1274140|char+blah[]+=+"blah+blah+Blah+BLAH+blAH\0";
int+i+=+0;
while(+blah[i]+%7C='+',+blah[%2B%2Bi]+)+{}|code-block|syntax|javascript|1274141|但是，如果你给它一些符号/数字，它就会爆炸，通常它是邪恶的。不过，面试问题问得好。|1274142|entityMap^0|A|9|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

If we're going to be as sloppy as to use <code>tolower()</code>, do this:
<pre><code>char blah[] = &quot;blah blah Blah BLAH blAH\0&quot;;
int i = 0;
while( blah[i] |=' ', blah[++i] ) {}
</code></pre>
But, well, it kinda explodes if you feed it some symbols/numerals, and in general it's evil. Good interview question, though.

blocks|key|1274161|text|循环指针以获得更好的性能：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1274162|#include+<ctype.h>

char*+toLower(char*+s)+{
++for(char+*p=s;+*p;+p%2B%2B)+*p=tolower(*p);
++return+s;
}
char*+toUpper(char*+s)+{
++for(char+*p=s;+*p;+p%2B%2B)+*p=toupper(*p);
++return+s;
}|code-block|syntax|javascript|1274163|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|$]]

Looping the pointer to gain better performance:

<pre class="lang-c prettyprint-override"><code>#include &lt;ctype.h&gt;

char* toLower(char* s) {
 for(char *p=s; *p; p++) *p=tolower(*p);
 return s;
}
char* toUpper(char* s) {
 for(char *p=s; *p; p++) *p=toupper(*p);
 return s;
}
</code></pre>

How can I convert a mixed case string to a lowercase string in C?

How do I lowercase a string in C?

如何在C中将大小写混合的字符串转换为小写字符串？

问如何在C中将字符串小写？
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