blocks|key|1838036|text|首先，C字符串(printf中的%25s+)应该以NUL结尾。你错过了终结者。试试char+a[]+=+{0x3f,+0x4d,+0}+(str也是如此)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1838037|其次，pstr和str指向相同的内存，所以您的memcpy是无操作的。与第一点相比，这是一个次要的观点。|1838038|entityMap^0|8|6|G|2|13|Q|1V|3|0|3|4|8|3|N|6|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]|$9|Q|A|R|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|I|$]]

Firstly, C strings (the <code>%s</code> in <code>printf</code>) are expected to be NUL-terminated. You're missing the terminators. Try <code>char a[] = {0x3f, 0x4d, 0}</code> (same goes for <code>str</code>).

Secondly, <code>pstr</code> and <code>str</code> point to the same memory, so your <code>memcpy</code> is a no-op. This is a minor point compared to the first one.

blocks|key|2269373|text|printf的%25s需要一个以0结尾的字符串，而你的字符串却不是。然而，你的数组后面未初始化的内存可能恰好以0字节开始，在这种情况下，你的代码看起来是正确的--它仍然是不正确的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2269374|entityMap^0|0|6|7|2|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

<code>printf</code>'s <code>%s</code> expects a 0-terminated string, your strings aren't. The uninitialized memory following your arrays may however happen to start with a 0-byte, in which case your code will appear to be correct - it still isn't.

blocks|key|1838167|text|添加一个null结束符，因为这正是printf所期望的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1838168|char+a[]+=+{0x3f,+0x4d,+'\0'};|code-block|syntax|javascript|1838169|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|$]]

Add a null terminator, cause that's what you printf expects:

<pre><code>char a[] = {0x3f, 0x4d, '\0'};
</code></pre>

blocks|key|218267|text|将一个数组声明为"str"，然后用pstr指向它。请注意，您没有以null结尾的字符，因此在使用memcpy之后，您可以按照字符串的要求将块复制到没有null结束符的自身。因此，printf无法找到字符串的末尾，并继续打印，直到找到0(或字符形式的'\0‘)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|218268|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|$]]

You're declaring an array "str", then pointing to it with pstr. Note that you have no null-terminating character, so after using memcpy you copy the block to itself with no null terminator, as a string requires. Thus, printf can't find the end of the string and continues printing until it finds a 0 (or '\0' in character terms)

blocks|key|2274883|text|C字符串的标准表示方式是，在内存中，它们是表示字符的非零字节序列，后跟一个零(或NULL)字节。您应该声明：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2274884|char+a[]+=+{0x3f,+0x4d,+0};|code-block|syntax|javascript|2274885|当您分配一个字符串指针(如在unsigned+char+*pstr+=+str;中)时，两个指针都指向相同的内存区域，因此也就指向相同的字符。不需要复制字符。|offset|length|style|CODE|2274886|当您确实需要复制字符时，您应该使用strlen()，sizeof()运算符返回其参数在内存中使用的字节数。sizeof(pointer)是指针使用的字节数，而不是字符串的长度。使用strlen()函数可以找到字符串的长度(即它在内存中所占的字节数)。此外，还有一些标准函数可以复制C字符串。你应该依靠这些来做正确的事情：|2274887|strcpy(pstr,+str);|2274888|entityMap^0|0|0|E|Q|0|H|8|Q|8|1H|F|2I|8|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@$I|V|J|W|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|X|8|@$I|Y|J|Z|K|L]|$I|10|J|11|K|L]|$I|12|J|13|K|L]|$I|14|J|15|K|L]]|9|@]|A|$]]|$1|O|3|P|5|D|7|16|8|@]|9|@]|A|$E|F]]|$1|Q|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|R|$]]

The standard way C strings are represented is that in memory, they are a sequence of non-zero bytes representing the characters, followed by a zero (or NULL) byte. You should declare:

<pre><code>char a[] = {0x3f, 0x4d, 0};
</code></pre>

When you assign a string pointer (as in <code>unsigned char *pstr = str;</code>) both pointers point to the same memory area, and thus the same characters. There is no need to copy the characters.

When you do need to copy characters, you should be using <code>strlen()</code>, the <code>sizeof()</code> operator returns the number of bytes its argument uses in memory. <code>sizeof(pointer)</code> is the number of bytes the pointer uses, not the length of the string. You find the length of a string (i.e. the number of bytes it occupies in memory) with the <code>strlen()</code> function. Also, there are standard functions to copy C strings. You should rely on those to do the right thing:

<pre><code>strcpy(pstr, str);
</code></pre>

blocks|key|1838307|text|同意。您必须在字符数组的末尾添加一个空字节。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1838308|char+a[]+=+{0x3f,+0x4d,+'\0'};|code-block|syntax|javascript|1838309|原因是您正在创建一个字符串，而没有声明它的实际结束位置。您的memcpy()函数将*str复制到*pstr，并自动为您添加一个空字节，这就是它工作的原因。|1838310|如果没有memcpy()，字符串永远不知道何时结束，所以它会到达后续的内存地址，并返回存储在那里的任何随机值。当你用字符创建一个字符串时，一定要记住以空字节结尾。|1838311|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Agreed. You'll have to add a null byte at the end of your array of chars.

<pre><code>char a[] = {0x3f, 0x4d, '\0'};
</code></pre>

The reason being is that you're creating a string without declaring where it actually ends. Your memcpy() function copies *str to *pstr and automatically adds a null byte for you, which is why it works.

Without memcpy() there the string never knows when to end, so it reaches into subsequent memory addresses and returns whatever random values are stored there. When you're creating a string out of characters, always remember to end it with a null byte.

I have some doubts in basic C programming.

I have a char array and I have to copy it to a char pointer. So I did the following:

<pre><code>char a[] = {0x3f, 0x4d};
char *p = a; 
printf("a = %s\n",a);
printf("p = %s\n",p);
unsigned char str[] = {0x3b, 0x4b};
unsigned char *pstr =str;
memcpy(pstr, str, sizeof str);
printf("str = %s\n",str);
printf("pstr = %s\n",pstr);
</code></pre>

My printf statements for pstr and str get appended with the data "a".
If I remove memcpy I get junk. Can some C Guru enlighten me?

Basic C question on copying char arrays to char pointers

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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我对基本的C编程有一些疑问。我有一个char数组，我必须将它复制到char指针。因此，我做了以下工作：char a[] = {0x3f, 0x4d};char *p = a;     printf("a = %s\n",a);printf("p = %s\n",p);unsigned char str[] = {0x3...

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