sizeof 和 strlen 的printf 问题

 1 #include <stdio.h>
 2 #include <string.h>
 3
 4 int main(void){
 5     char temp[3];
 6     scanf("%s", temp);
 7     printf("%d\n", sizeof(temp));
 8     printf("%d\n", strlen(temp));
 9     printf("%s\n", temp);
10 }

编译时出错：

test_scanf.c: In function ‘main’:
test_scanf.c:7:2: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘long unsigned int’ [-Wformat=]
  printf("%d\n", sizeof(temp));
  ^
test_scanf.c:8:2: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘size_t’ [-Wformat=]
  printf("%d\n", strlen(temp));
  ^

sizeof() 和 strlen() 返回值类型为size_t

In C99‘s *printf, z is a length modifier like h or l, not a conversion specifier like d or u.

将代码改为：

printf("%zu\n", sizeof(temp));
printf("%zu\n", strlen(temp));

另外：

strlen 计算到\0 出现为止。

sizeof 保证能容纳实现所建立的最大对象的字节大小。