c - 字符数组的文字字符串初始值设定项

Question

在数组衰减为指针的情况下有以下规则:

An lvalue [see question 2.5] of type array-of-T which appears in an expression decays (with three exceptions) into a pointer to its first element; the type of the resultant pointer is pointer-to-T.

(The exceptions are when the array is the operand of a sizeof or & operator, or is a literal string initializer for a character array.)

如何理解数组是“字符数组的文字字符串初始值设定项”的情况？请举个例子。

谢谢!

Answer 1

数组不会衰减为指针的三个异常(exception)情况如下:

异常(exception) 1. — 当数组是 sizeof 的操作数时。

int main()
{
   int a[10];
   printf("%zu", sizeof(a)); /* prints 10 * sizeof(int) */

   int* p = a;
   printf("%zu", sizeof(p)); /* prints sizeof(int*) */
}

异常(exception) 2. — 当数组是 & 运算符的操作数时。

int main()
{
    int a[10];
    printf("%p", (void*)(&a)); /* prints the array's address */

    int* p = a;
    printf("%p", (void*)(&p)); /*prints the pointer's address */
}

异常 3. — 当数组用文字字符串初始化时。

int main()
{
    char a[] = "Hello world"; /* the literal string is copied into a local array which is destroyed after that array goes out of scope */

    char* p = "Hello world"; /* the literal string is copied in the read-only section of memory (any attempt to modify it is an undefined behavior) */
}