Question

I’ve just started using Visual Studio (I got VS 2012 from dreamspark, and it hasn’t been long since I’ve started using Windows again) and I’m having some trouble.

I have a single file named “main.c” under my Source Files folder that looks like this:

#include <stdio.h>

typedef struct S_s S;
struct S_s {
    void* x;
};

int main(int argc, char** argv)
{
    int N;
    scanf("%d", &N);

    S* s;
    printf("%p", s);

    return 0;
}

And when I try to build it gives me the following error messages:

Error   3   error C2065: 's' : undeclared identifier    c:\users\math4tots\documents\visual studio 2012\projects\algorithms\lecture1\main.c 13  1   Lecture1
Error   4   error C2065: 's' : undeclared identifier    c:\users\math4tots\documents\visual studio 2012\projects\algorithms\lecture1\main.c 14  1   Lecture1
Error   2   error C2275: 'S' : illegal use of this type as an expression    c:\users\math4tots\documents\visual studio 2012\projects\algorithms\lecture1\main.c 13  1   Lecture1

The funny thing is that it builds just fine if I comment out the scanf line.

I did create an “Empty project” under the “Visual C++” options so I wasn’t sure if VS compiled it as a C or C++ program. However, I was under the impression that my code was C/C++ agnostic enough that it should compile in either C or C++.

What can I do to get this to build while still maintaining the semantics of the program?

Answer 1

The code is legal C++ and legal C99, but not legal C89. Variable declarations in C89 must come at the beginning of a block, so having S* s; after scanf("%d", &N);
is not OK in C89.