Linking files together with headers

[Nielyboyken]

Hello

I've got problems linking my files together.
Take, I've got two files.
A main-file and a sub-file.

The sub-file contains a void function which needs to be used in the main-file.

main-file:

#include <iostream>
#include "subfile.h"

using namespace std;
int main() {
plus(5, 11);
cout << result <<endl;
}

sub-file:

void plus(int x, int y) {
result = x + y;
}

How can I do that?

Thanks for reading,
Niely

[shadowCODE]

g++ -o output main.cpp sub-file.cpp

[benbalach]

On line 6 in the main-file you are trying to print an undefined variable. The plus() function should return a value and you should assign that value to a variable and then print the variable.

main.cpp

#include <iostream>
#include "subfile.h"

using namespace std;
int main() {
  int result = plus(5, 11);
  cout << result <<endl;
}

subfile.h

int plus(int x, int y) {
  result = x + y;
  return result
}

[Nielyboyken]

Did your exact code. Got an error back:

sub.h: In function ‘void plus(int, int)’:
sub.h:3:8: error: return-statement with a value, in function returning 'void' [-fpermissive]
 return result;
        ^
plFTP.cpp: In function ‘int main()’:
plFTP.cpp:6:3: error: reference to ‘plus’ is ambiguous
   plus(5, 11);
   ^
In file included from plFTP.cpp:2:0:
sub.h:1:6: note: candidates are: void plus(int, int)
 void plus(int x, int y) {
      ^
In file included from /usr/include/c++/4.8/string:48:0,
                 from /usr/include/c++/4.8/bits/locale_classes.h:40,
                 from /usr/include/c++/4.8/bits/ios_base.h:41,
                 from /usr/include/c++/4.8/ios:42,
                 from /usr/include/c++/4.8/ostream:38,
                 from /usr/include/c++/4.8/iostream:39,
                 from plFTP.cpp:1:
/usr/include/c++/4.8/bits/stl_function.h:140:12: note:                 template<class _Tp> struct std::plus
     struct plus : public binary_function<_Tp, _Tp, _Tp>
            ^
plFTP.cpp:7:10: error: ‘result’ was not declared in this scope
   cout<< result;

[benbalach]

I apologize. This just goes to show that you should always test your code before giving it to someone else to use.

main.cpp

#include <iostream>
#include "subfile.h"

int main() {
  int result = plus(5, 11);
  std::cout << result << std::endl;
}

subfile.h

int plus(int x, int y) {
  int result = x + y;
  return result;
}

Line 20 of your compiler errors is an example why you should not use using directives.

[Nielyboyken]

So with 'using namespace std' this isn't working?
Why not, is it possible with it as well a small other way around?

[benbalach]

It is possible, but you shouldn't. Have a look at Namspace Rule #1:

http://www.gotw.ca/publications/migrating_to_namespaces.htm

[Nielyboyken]

I understand what the error cause was. :)
namespacing influenced the plus function, renaming that one fixed it.

Thanks all! :)

[TheIdeasMan]

Hi,

Just a point:

Don't rename your functions to avoid the namespace clash, instead get rid of using namespace std; . Put std:: before each std thing.

There is lots written about that Google it :+)

Happy New year, hope all is well at your end :+D

[Nielyboyken]

Okay thanks! :)
Everything is fine now.

Thanks a lot for all your help.