Can I initial a static global variable by calling a function in C language?

Question

Can I initial a static global variable by calling a function in C language? For example:

static int var_01 = fun();

When I use this in VC6 it succeed. But it failed in GCC 4.6.1. This is very strange. I guess this usage is illegal in C89? Or other reason cause this?

You'll need to initialise it to a compile-time constant, so in general no. (Perhaps yes if your function is actually a macro.) — sapi
– sapi, Commented Aug 1, 2014 at 3:06
@sapi The fun() is an ordinory function.It's strange that it can compile ok with VC6. — Ezio
– Ezio, Commented Aug 1, 2014 at 3:12
@Ezio: Are you sure you are compiling it as C, as opposed to C++? It is valid in C++, but not in C. — AnT stands with Russia
– AnT stands with Russia, Commented Aug 1, 2014 at 3:16
@AndreyT I edit this in C file,so I think it should be in C.But as you said,I guess VC may compile it with C++ features. — Ezio
– Ezio, Commented Aug 4, 2014 at 3:23

Shafik Yaghmour · Accepted Answer · 2014-08-01 14:09:29Z

In C99 and as far as I know in C89 as well an initializer for an object with static storage duration has to be either a constant expression or an string literal, from the draft C99 standard section 6.7.8 Initialization:

All the expressions in an initializer for an object that has static storage duration shall be constant expressions or string literals.

and a function call is not a constant expression from section 6.6 Constant expressions which says (emphasis mine):

Constant expressions shall not contain assignment, increment, decrement, function-call, or comma operators, except when they are contained within a subexpression that is not evaluated.98)

gcc generates the same error using both -std=c99 and -std=c89, note I am also using the following flags -Wall -Wextra -pedantic.

In the modern versions of Visual Studio compiler this does not work in C(see it live) but in C++ this does work. So it may be that you are compiling it as C++ in Visual Studio.

paul · Accepted Answer · 2014-08-01 03:14:50Z

1

Because your post is tagged with c. In c, this is a compile error. You must initialize that to constat literals.

See: http://www.geeksforgeeks.org/g-fact-80/

answered Aug 1, 2014 at 3:14

paul

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