用细绳的sizeof行为 [英] Behaviour of sizeof with string

问题描述

‪#‎include‬ <stdio.h>
#include <string.h>
int main()
{
    printf("%d\n",sizeof("S\065AB"));
    printf("%d\n",sizeof("S65AB"));
    printf("%d\n",sizeof("S\065\0AB"));
    printf("%d\n",sizeof("S\06\05\0AB"));
    printf("%d\n",sizeof("S6\05AB"));
    printf("%d\n",sizeof("\0S65AB"));
    return 0;
}

输出：

5
6
6
7
6
7

http://ideone.com/kw23IV

任何人都可以用字符串解释这种现象？

Can anyone explain this behaviour with character strings?

在Debian 7.4使用GCC

Using GCC on Debian 7.4

推荐答案

字符串文字的大小内的字符包括添加了结尾的空字节数。如果存在嵌入字符串中的空值，它们是不重要的;他们得到计数。这是无关的的strlen（）只是如果文字不包含嵌入的空值，的strlen（S）==的sizeof（S） - 1 。

The size of a string literal is the number of characters in it including the trailing null byte that is added. If there embedded nulls in the string, they are immaterial; they get counted. It is unrelated to strlen() except that if the literal includes no embedded nulls, strlen(s) == sizeof(s) - 1.

printf("%zu\n", sizeof("S\065AB"));      // 5: '\065' is a single character
printf("%zu\n", sizeof("S65AB"));        // 6
printf("%zu\n", sizeof("S\065\0AB"));    // 6: '\065' is a single character
printf("%zu\n", sizeof("S\06\05\0AB"));  // 7: '\06' and '\05' are single chars
printf("%zu\n", sizeof("S6\05AB"));      // 6: '\05' is a single character
printf("%zu\n", sizeof("\0S65AB"));      // 7

注意'\\ 377'是一个有效的八进制常量，相当于'\\ XFF或255。您可以在字符串中使用它们了。值'\\ 0'是仅一个更一般的八进制常数的一个特例。

Note that '\377' is a valid octal constant, equivalent to '\xFF' or 255. You can use them in strings, too. The value '\0' is only a special case of a more general octal constant.

注意的sizeof（）计算为类型的值为size_t ，并在C99正确的格式类型修饰符和C11为为size_t 是以Z ，并且因为它是无符号， U 比更合适 D ，所以我使用了％祖\\ N格式。

Note that sizeof() evaluates to a value of type size_t, and the correct formatting type qualifier in C99 and C11 for size_t is z, and since it is unsigned, u is more appropriate than d, hence the "%zu\n" format that I used.

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