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Can I initialize an empty 2D C string like this?

Can I initialize an empty 2-dimentional C string like this?

int function(void){
  char s[50][50]={{}};
}

I'm not sure if string s will be initialized as empty when it's defined in a function like this.

Solution

  • No, you may not, if you want your code to be portable C:

    % gcc -pedantic-errors -c init.c 
init.c: In function ‘function’:
init.c:2:19: error: ISO C forbids empty initializer braces [-Wpedantic]
   char s[50][50]={{}};
                   ^

    It is a GCC extension. However you can add a single zero in the braces:

    char s[50][50] = {{0}};

    or even within just one set of braces:

    char s[50][50] = {0};

    it will find the first scalar element and initialize it with the given value, and rest of the elements not explicitly initialized will be initialized as if they had a zero initializer. (Note: you could use say 42 for the one element, and rest of them would be still initialized to zero).

    Or, since these are arrays of char, you can use a string in braces:

    char s[50][50] = {""};

    This will initialize s[0] with the empty string.

    The empty initializer ({ }) of GCC is needed for another extension - initialization of zero-length flexible array members. It does not exist just to be a generic shorthand.

    Standard C does not support initialization of flexible array members, nor does it support arrays of length zero.