How to define function in other source file:C++ CodeBlocks

问题

I am trying to separate my functions in another source file. But i am getting error that multiple definition on add function.

Main source file

Main.cpp

#include<iostream>
#include "myHeader.h"
using namespace std;

int main()
{
int result = add(1,2);
}

Header file "myHeader.h"

#include "calc.cpp"
int add(int, int);

Other Source file "calc.cpp"

int add(int a, int b)
{
return a+b;
}

回答1:

Don't include calc.cpp from myHeader.h. Except for that one line, your example is right as far as headers go. (main() should return a value).

calc.cpp and main.cpp are two different "compilation units" which will be compiled separately into object files. The two object files are then combined into one executable by a linker.

回答2:

What you need is:

"myHeader.h"

#ifndef MY_HEADER
#define MY_HEADER
 int add(int, int);
#endif

calc.cpp

#include "myHeader.h"

int add(int a, int b)
{
 return a+b;
}

main.cpp

#include "myHeader.h"

int main()
{
  int result = add(1,2);
  return 0;
}

You don't include the .cpp into the .h . The header file is used to tell the compiler the existence of a function with the specified prototype, but the liker will be tke care of matching up the call to a function with the implementation of that function.

Also, it's usually a good idea to give you header file and .cpp the same name, so calc.h and calc.cpp rather than myHeader.h.

回答3:

You problem is that you include a Code File (cpp) into a header. You should do the inverse. Include your header "myHeader.h" into calc.cpp. And to be coherent, you should name your header the same name as your Code file, so calc.h for the header and calc.cpp for you code.

回答4:

#include "calc.cpp"

Don't do that - it includes the function definition in any translation unit that includes the header, so you'll end up with multiple definitions.

Without that, your code should be fine if you build a program from both source files. main.cpp will include a declaration, so that it knows that function exists; the definition from the other source file will be included in the program by the linker.

回答5:

This is pretty simple. Do not Include your "calc.cpp" file in "MyHeader.h" file.

Take also a look at C/C++ IncludeGuard here

This is a fundamental of C/C++ programming. You will need to use it many times.

Protect your "myHeader.h"

#ifndef ADD_HEADER
#define ADD_HEADER
 int add(int, int);
#endif // ADD_HEADER

回答6:

Do not include calc.cpp . This is causing the redefinition

you can include myHeader.h in calc.cpp

来源：https://stackoverflow.com/questions/21167521/how-to-define-function-in-other-source-filec-codeblocks

标签

c++

header-files