odd multiple declaration?

I have three files:

TestA.cpp:

Code:

---


#include "CmnFunc.cpp"

---

and TestB.cpp

Code:

---


#include "CmnFunc.cpp"

---

and CmnFunc.cpp:

Code:

---


#ifndef CMNFNC
#define CMNFNC

int randInt(int start, int end){

...


}

#endif

---

Compiing with 'g++ TestA.cpp TestB.cpp' gives a multiple definition error. I thought the #ifndef bit would protect against this? Any ideas?

Thanks very much

Do not include source files, include header files instead.

I know but shouldn't the #ifndef protect anyway??

Those inclusion guards only work per file. If you have two source files, you get multiple definitions. One per file :)

makes sense i guess, thanks!

If you insist on including implementations in other files, you should at the very least declare them "inline" and use a .h extension, not a .cpp extension.

I'm not using the code, just asking for an explanation of the behavior thanks

The explanation is that;

1) TestA.cpp is compiled to a TestA.o which has a single definition of your randInt() function.

2) TestB.cpp is compiled to a TestB.o which has a single definition of your randInt() function.

3) The include guards in CmnFunc.cpp mean that, if TestA.cpp or TestB.cpp was to #include CmnFunc.cpp more than once, then statements 1 and 2 are still true.

4) The linker, when it attempts to build your executable from TestA.o and TestB.o (and any other object or library files it links in) encounters a definition of randInt() in both TestA.o and TestB.o. In other words, it encounters two definitions. Hence it complains about a multiple definition.