Question

I want to check an array in a condition. Let’s take this simple code below:

#include <stdio.h>
int main()
{
    int array[] = {1,2,3,4,5}; // initializing an array
    if(array[] == {1,2,3,4,5}) // using as condition
    {
         printf("worked");
    }
    else printf("not worked");

    return 0;
}

But it gives an error:

In function 'main':|
C:\Python32\Untitled4.c|5|error: expected expression before ']' token|
||=== Build finished: 1 errors, 0 warnings ===|

So how should I use an array in a condition?

Answer 1

If you have a modern C compiler, at least C99, you can use a compound literal and a function to do that comparison:

if(memcmp(array, (int[]){1,2,3,4,5}, sizeof array) == 0) {
   printf("worked");
}

• Here memcmp (memory compare) compares the data to which the two
  pointers point.
• (int[]){1,2,3,4,5} is the compound literal, something with the type in () and then an initializer in { } as you have in the declaration of your variable.
• the two arrays are converted to pointers to their first elements when used like in expressions like that

Edit: As Eric correctly remarks, memcmp is only a valid comparison if the base type of your array (here this is int) has no padding bits or bytes. For int this is uncommon these days, so what I describe is fine on usual platforms. If you’d have other, more complex, data types some day, you would have to write your own comparison function for arrays of that type.