Question

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gcc compile error: cast specifies array type

I want to check the difference in (int * ) and (int []). When I compile the following code, line one goes fine. But for line 2, my compiler gives the following error:

test.c:10: error: cast specifies array type

Can any one please tell me the meaning of this error and where have I erred?

#include<stdio.h>

void abc(int *a)
{
        int i;
        for(i=0;i<2;i++)
        {
            printf("%d",((int * )a)[i]);  //(1)
            printf("%d",((int [])a)[i]); //(2)
        }
}

int main()
{
    int b[2]={0,1};
    abc(b);
    return 0;
}

Answer 1

In general int * is a pointer (to an integer) and int[] is an array of unspecified size, which is a so called incomplete type. Incomplete types can only be used in declarations and must be completed in definitions. For example (the following code lies in global scope):

extern int[] p; //declaration of p

int p[5]; //definition of p - size must be specified

When you talk about function parameters, it’s a whole other story. The declarations:

void f(int *p)

and

void f(int p[])

will be identical. It’s just syntactic sugar if you will.

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Edit: Other than that: If you are asking what’s the difference between arrays and pointers: Everything! I’d link you to C-faqs.com for more concrete answers.