练习 8：大小和数组

#include <stdio.h>

int main(int argc, char *argv[])
{
    int areas[] = {10, 12, 13, 14, 20};
    char name[] = "Zed";
    char full_name[] = {
        'Z', 'e', 'd',
         ' ', 'A', '.', ' ',
         'S', 'h', 'a', 'w', '\0'
    };

    // WARNING: On some systems you may have to change the
    // %ld in this code to a %u since it will use unsigned ints
    printf("The size of an int: %ld\n", sizeof(int));
    printf("The size of areas (int[]): %ld\n",
            sizeof(areas));
    printf("The number of ints in areas: %ld\n",
            sizeof(areas) / sizeof(int));
    printf("The first area is %d, the 2nd %d.\n",
            areas[0], areas[1]);

    printf("The size of a char: %ld\n", sizeof(char));
    printf("The size of name (char[]): %ld\n",
            sizeof(name));
    printf("The number of chars: %ld\n",
            sizeof(name) / sizeof(char));

    printf("The size of full_name (char[]): %ld\n",
            sizeof(full_name));
    printf("The number of chars: %ld\n",
            sizeof(full_name) / sizeof(char));

    printf("name=\"%s\" and full_name=\"%s\"\n",
            name, full_name);

    return 0;
}

将full_name最后的'\0'去掉，并重新运行它，在valgrind下再运行一遍。现在将full_name的定义从main函数中移到它的上面，尝试在Valgrind下运行它来看看是否能得到一些新的错误。有些情况下，你会足够幸运，不会得到任何错误。

去掉 '\0'：无报错；移动至 main 上：无报错。

将areas[0]改为areas[10]并打印，来看看Valgrind会输出什么。

The first area is 76098960, the 2nd 12. Valgrind 无报错。

尝试上述操作的不同变式，也对name和full_name执行一遍。

同上。

附加题 1

尝试使用areas[0] = 100;以及相似的操作对areas的元素赋值。

可以正常赋值。

附加题 2

尝试对name和full_name的元素赋值。

⮞ make ex8
cc -Wall -g                                                      -c ex8.c -o ex8.o
ex8.c: In function ‘main’:
ex8.c:16:14: error: assignment to expression with array type
   16 |         name = "A";
      |              ^
make: *** [Makefile:13: ex8.o] Error 1

尝试使用 strcpy 函数，需补充string.h并避免越界。

ex8.c: In function ‘main’:
ex8.c:16:9: warning: implicit declaration of function ‘strcpy’ [-Wimplicit-function-declaration]
   16 |         strcpy(name, "Qidi");
      |         ^~~~~~
ex8.c:2:1: note: include ‘<string.h>’ or provide a declaration of ‘strcpy’
    1 | #include <stdio.h>
  +++ |+#include <string.h>
    2 |
ex8.c:16:9: warning: incompatible implicit declaration of built-in function ‘strcpy’ [-Wbuiltin-declaration-mismatch]
   16 |         strcpy(name, "Qidi");
      |         ^~~~~~
ex8.c:16:9: note: include ‘<string.h>’ or provide a declaration of ‘strcpy’
ex8.c:16:9: warning: ‘__builtin_memcpy’ writing 5 bytes into a region of size 4 overflows the destination [-Wstringop-overflow=]
   16 |         strcpy(name, "Qidi");
      |         ^~~~~~~~~~~~~~~~~~~~
ex8.c:12:10: note: destination object ‘name’ of size 4
   12 |     char name[] = "Zed";
      |          ^~~~
cc  -o ex8 ex8.o

附加题 3

尝试将areas的一个元素赋值为name中的字符。

areas[0] = name[0] → The first area is 90, the 2nd 12. 以 ASCII 码赋值。

附加题 4

上网搜索在不同的CPU上整数所占的不同大小。

• x86 架构：通常采用 ILP32 数据模型，即 int、long 和指针都是 32 位。

• x86-64 或 AMD64 架构：通常采用 LP64 数据模型，即 int 是 32 位，而 long 和指针是 64 位。