这在C int（* ptr [2]）[4]中是什么意思；

Question

I want to know what is the meaning of the definition

int (*ptr[2])[4];

If i print the size of "ptr", it displays 16. Also on my machine size of integer pointer is giving 8, where as size of integer is 4.

If i redifine ptr as ,

int (*ptr[2]); then also, size of ptr is 16.

so questions are

1. what is the meaning of definition int (*ptr[2])[4];
2. How do i initialize ptr?

Answer 1

Use the right-left rule to read such declarations.

int (*ptr[2])[4] is an array of 2 pointers to arrays of 4 integers.

If i print the size of "ptr", it displays 16. Also on my machine size of integer pointer is giving 8

This is because ptr is an array of 2 pointers.

Answer 2

Q2 How do i initialize ptr?

Eg,

int a[4] = { 1, 2, 3, 4};
int b[4] = { 6, 7, 8, 9};
int (*ptr[2])[4] = { &a, &b };
int i;
for(i = 0; i<4;++i){
    printf("%d ", (*ptr[0])[i]);//a
}
printf("\n");
for(i = 0; i<4;++i){
    printf("%d ", (*ptr[1])[i]);//b
}
printf("\n");

,

Answer 3

int (*ptr[2])[4]; is an array which has 2 elements, the type of each element is int (*) [4] , that stands for an pointer which point an array which has 4 element.

this is equal to typedef int (* PTR) [4]; PTR ptr[2]; typedef int (* PTR) [4]; PTR ptr[2];

typedef int (*arrayOfNPointers)[N];

So, if this is right, it is a data type describing an array of N pointers to int.