Question

Is it possible to create anonymous, ad-hoc arrays in C?

For example, suppose I have a function called processArray(int[] array) that takes an int array as its argument, can I pass it an anonymous array in the following way:

int main(){
 processArray( (int[]){0, 1, 2, 3} ); //can I create this type of array?
 return 0;
}

Or do I have to declare the array previously (with a pointer), and then pass its pointer to processArray()? For example:

int main(){
 int[] myArray = {0, 1, 2, 3};
 processArray(myArray);
 return 0;
}

Answer 1

With C99 and C11, you can write what you wrote, as exemplified by the following code. These are ‘compound literals’, described in ISO/IEC 9899:2011 §6.5.2.5 Compound literals (and it is the same section in ISO/IEC 9899:1999).

#include <stdio.h>

static void processArray(int n, int arr[])
{
    for (int i = 0; i < n; i++)
       printf(" %d", arr[i]);
    putchar('\n');
}

int main(void)
{
    processArray(4, (int[]){0, 1, 2, 3});
    return 0;
}

When run, it produces the answer:

 0 1 2 3