Question

I’ve run into a problem that seems to not be addressed by any of the C Standards after C89 save for the mention that structures initialization limits had been lifted. However, I’ve run into an error using the Open Watcom IDE (for debugging) where the compiler states that the initializer must be a constant expression.

Here’s the gist of what’s going on.

typedef struct{
 short x;
 short y;

} POINT;

void foo( short x, short y )
{
 POINT here = { x, y }; /* <-- This is generating the error for the compiler */

 /* ... */

}

Any ideas why, or what standard disallows that?

Answer 1

The following quote is from the C99 rationale:

The C89 Committee considered proposals for permitting automatic
aggregate initializers to consist of a brace-enclosed series of
arbitrary execution-time expressions, instead of just those usable for
a translation-time static initializer. Rather than determine a set of
rules which would avoid pathological cases and yet not seem too
arbitrary, the C89 Committee elected to permit only static
initializers. This was reconsidered and execution-time expressions are
valid in C99.