Code that compiles with gcc will not compile in visual studio 2012

Question

I am very new to procedural programming, so I am not sure if my code is bad or if I am doing something wrong in Visual Studio.

So I have this bit of code that is supposed to print an integer, print it's location in memory, change it's value through memory and then print the new integer as well as it's location in memory.

It compiles and runs fine through the cmd with gcc, but not in Visual Studio.

#include <stdio.h>

int main(){
    int a = 4;
    printf("Integer is: %d\n", a);
    printf("Integer is stored at: %p in memory\n", a);
    int *pointer = &a;
    *pointer = 3;
    printf("Integer is now: %d at %p in memory\n",a,*pointer);
    getchar();
    return 0;
}

Visual studio gives me these errors when I try to compile and run:

line 9: error C2065: 'pointer' : undeclared identifier

line 9: error C2100: illegal indirection

line 11: error C2065: 'pointer' : undeclared identifier

line 11: error C2100: illegal indirection

So what you're saying is, two different versions of C are different? There's not one "C" ... there's several different versions/iterations of the spec each with their own features. — Brian Roach, Jan 19 '13 at 22:04
This might help: http://stackoverflow.com/questions/14376511/cannot-declare-variable-at-all-with-windows-driver-kit-build-environment/14377441#14377441 — hmjd, Jan 19 '13 at 22:06
Visual Studio is probably complaining you're not following the ANSI C standard: you cannot declare any new variables below any statements. If you want to, switch to C99 or C++. — Orwell, Jan 19 '13 at 22:07
See also: http://stackoverflow.com/questions/9903582/error-c2275-illegal-use-of-this-type-as-an-expression/9903698#9903698 — rubenvb, Jan 19 '13 at 22:21

ldav1s · Answer 1 · 2013-01-19T22:13:05.667

5

The Visual Studio C compiler does not support C99, in particular being able to declare variables at any place in a block. GCC supports several revisions of the C language. IIRC, passing in -std=c89 as a flag to gcc will flag these also.

edited Jan 19 '13 at 22:13

answered Jan 19 '13 at 22:07

ldav1s

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score 2 · Answer 2 · edited Jan 20 '13 at 09:44

I think you should first declare the variables on top of the function,and when you print memory address with %p you should give the address of the variable to be printed

try this

int main()
{
    int a = 4;
    int *pointer=&a;
    printf("Integer is: %d\n", a);
    printf("Integer is stored at: %p in memory\n",&a);
    *pointer = 3;
    printf("Integer is now: %d at %p in memory\n",a,pointer);
    getchar();
    return 0;
}

score 1 · Answer 3 · answered Jan 19 '13 at 22:07

1

printf("Integer is stored at: %p in memory\n", a); You need to take the address of a as in &a.

printf("Integer is now: %d at %p in memory\n",a,*pointer); You need not dereference pointer to get the address. Use pointer, not *pointer

If you're compiling with a C89 (I think) or older compiler, the declaration of pointer will have to be moved to the top of a block. You cannot declare variables in the middle of code in older C.

answered Jan 19 '13 at 22:07

JimR

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Where is the explanation for the -1? – JimR Jan 20 '13 at 05:11
1

You are right with what you say, and I don't understand the -1 either. +1 from me. – NlightNFotis Jan 20 '13 at 09:26

score 1 · Answer 4 · answered Jan 19 '13 at 22:29

With VS2012 / C you need to add blocks in order to do what you want, unfortunately the compiler doesn't support declarations in the middle

int main(){
    int a = 4;
    printf("Integer is: %d\n", a);
    printf("Integer is stored at: %p in memory\n", a);
    {
      int *pointer = &a;
      *pointer = 3;
      printf("Integer is now: %d at %p in memory\n",a,*pointer);
    }
    getchar();
    return 0;
}

alternatively you can force to compile your .c file as a .cpp file by specifying the /TP switch on the file.

Code that compiles with gcc will not compile in visual studio 2012

4 Answers4