Why the size of pointer to array is always 8 in C?

问题:

This question already has answers here:

What is the size of a pointer? What exactly does it depend on? (2 answers)

Closed 5 years ago.

Belows are simple code that compares size of array itself and size of pointer to array.

#include <stdio.h>    
int main(){   
        int kkarray[100]= {1,0,};
        int (*kkpointer) = kkarray;

        printf("size of array using array itself : %ld \n" , sizeof(kkarray));        
        printf("size of array using pointer to array : %ld \n" , sizeof(kkpointer));   
}

but the result is,

400
8

I could understand that the first value is 400, but second one,, i think that it also should be 400 because as i assigned a pointer that points to array, kkpointer, it kinda acts like name of array, which is const address value. For example, i can get the first value of array using kkpointer[0]. I want to know why i got '8' instead of 400. I don't think the '8' is the size of address itself. please let me know. Thanks

回答1:

The size of any pointer is always 8 on your platform, so it's platform dependent.

The sizeof operator doesn't care where the pointer is pointing to, it gives the size of the pointer, in the first case it just gives the size of the array, and that is not the same.

This is a quote from § 6.5.3.4, ¶ 2 N1570 draft

The sizeof operator yields the size (in bytes) of its operand, which may be an expression or the parenthesized name of a type. The size is determined from the type of the operand. The result is an integer. If the type of the operand is a variable length array type, the operand is evaluated; otherwise, the operand is not evaluated and the result is an integer constant

and § 6.5.3.4, ¶ 4

When sizeof is applied to an operand that has type char, unsigned char, or signed char, (or a qualified version thereof) the result is 1. When applied to an operand that has array type, the result is the total number of bytes in the array.103) When applied to an operand that has structure or union type, the result is the total number of bytes in such an object, including internal and trailing padding

so as you can see, when applied to the array, it gives the total bytes. But if you pass a pointer, then the result will be the size of it's type.