Question

static char st[][8192];
void foo ( int tab_size){
    st = (char**) malloc ((tab_size+1)*sizeof(char)*8192);
}

I receive the compilation error in “malloc” line that st has incomplete type. What is wrong? Thanks.

Answer 1

Since you don’t specify the size of the inner dimension for st, the compiler doesn’t know how big it needs to be; hence the type is incomplete, and you never complete it before the malloc call.

Since it looks like your intent is to allocate st dynamically, go with Oli’s advice and declare it as a pointer to an 8192-element array of char:

static char (*st)[8192];

and rewrite your malloc statement as

st = malloc(sizeof *st * (tab_size+1));

sizeof *st == sizeof (char [8192]) == 8192. This form is a bit cleaner and easier to read. Note also that in C, you don’t have to cast the result of malloc (unless you’re using a pre-C89 implementation, in which case, I’m sorry), and the practice is discouraged.

This will allocate enough space to hold tab_size + 1 arrays of 8192 characters each.

It is only within the context of a function parameter declaration that T a[] declares a as a pointer to T.