Calling a function from a static class

Question

So the title is somewhat misleading. But its exactly what I am trying to do. I created a small case scenario. This case works in Visual Studio but when trying it on Mingw I get an error. Here is the case. I am trying to call a function inside a cpp file from a static method which resides in a different cpp file. This is just rough code which will get my point across.

File:foo.h

#ifndef FOO_H_INCLUDED
#define FOO_H_INCLUDED

#include <iostream>

struct foo
{
    int someMethod();
};


#endif // FOO_H_INCLUDED

File: foo.cpp

#include "foo.h"

int someFunction()
{
    std::cout << "SomeFunction";
    return 0;
}

int foo::someMethod()
{
  std::cout << "foo called";
  return 0;
}

File:main.cpp

void myfunction()
{

}

struct bar
{
    static void somebar()
    {
       someFunction(); //error: 'someFunction' was not declared in this scope
       myfunction(); //OK

    }
};

int main()
{

}

My question is why am I getting an error on someFunction(); This is my compiler output

g++.exe -Wall -std=c++98 -g -std=c++11 -I..\..\..\mingw64\include -c C:\Users\peeru\TestCodeBlocks\foo.cpp -o obj\Debug\foo.o
C:\Users\peeru\TestCodeBlocks\foo.cpp: In function 'int someFunction()':
C:\Users\peeru\TestCodeBlocks\foo.cpp:6:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^
C:\Users\peeru\TestCodeBlocks\foo.cpp: In member function 'int foo::someMethod()':
C:\Users\peeru\TestCodeBlocks\foo.cpp:11:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^
g++.exe -Wall -std=c++98 -g -std=c++11 -I..\..\..\mingw64\include -c C:\Users\peeru\TestCodeBlocks\main.cpp -o obj\Debug\main.o
C:\Users\peeru\TestCodeBlocks\main.cpp: In static member function 'static void bar::somebar()':
C:\Users\peeru\TestCodeBlocks\main.cpp:14:21: error: 'someFunction' was not declared in this scope
        someFunction();
                     ^
Process terminated with status 1 (0 minute(s), 0 second(s))
1 error(s), 2 warning(s) (0 minute(s), 0 second(s))

Any suggestions ?

someFunction is not visible in Main.cpp. Add extern int someFunction() at the top of Main.cpp, or add in foo.h and include foo.h in Main.cpp — LPs
– LPs, Commented Feb 26, 2015 at 15:17
Also of note: foo::someMethod is not static, and thus will require a foo object. — crashmstr
– crashmstr, Commented Feb 26, 2015 at 15:20

Mike Seymour · Accepted Answer · 2015-02-26 15:17:33Z

1

As the compiler says, someFunction hasn't been declared in main.cpp, only in a separate translation unit, foo.cpp. Functions need to be declared before use.

Add a declaration in either main.cpp, or a header included from both:

int someFunction();

You also need to return something from the functions that claim to return int, as the other warnings say.

answered Feb 26, 2015 at 15:17

Mike Seymour

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Stefano Sanfilippo · Accepted Answer · 2015-02-26 15:17:59Z

1

You have to provide a declaration for the function in main.cpp too, modify the foo.h header accordingly:

#ifndef FOO_H_INCLUDED
#define FOO_H_INCLUDED

#include <iostream>

int someFunction();

struct foo
{
    int someMethod();
};


#endif // FOO_H_INCLUDED

and add #include "foo.h" in main.cpp.

I am not sure why MSVC++ compiled without complaining, though.

answered Feb 26, 2015 at 15:17

Stefano Sanfilippo

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1 Comment

Rajeshwar Over a year ago

That was what I was curious about.

KernelPanic · Accepted Answer · 2015-02-26 15:12:07Z

0

Method someFunction and all others are declared as returning type int. So, add return 0 at the end of functions or declare them as void. And you cannot call non static function from static function.

answered Feb 26, 2015 at 15:12

KernelPanic

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4 Comments

Mike Seymour Over a year ago

That explains the warnings; but the question is about the error.

Rajeshwar Over a year ago

That has totally nothing to do with the answer

Mike Seymour Over a year ago

"you cannot call non static function from static function" - nonsense, of course you can. The only problem here is that the function hasn't been declared.

Rajeshwar Over a year ago

I know it looks simple. Visual Studio has no problem with it

Gadi · Accepted Answer · 2015-02-26 15:22:35Z

0

You declared someFunction() in foo.cpp, but not in main.cpp. When main.cpp is compiling, it doesn't know the declaration of someFunction(), so it fails.

You need to:

add int someFunction(); to the top of main.cpp
add int someFunction(); to the foo.h file, and then #include "foo.h" in main.cpp

answered Feb 26, 2015 at 15:22

Gadi

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