Building a temporary `main()` function in c++ - c++

Question

I'm just learning c++. I have a main.cpp unit which has a lot of stuff in it already, and I just want to build a quick little testMain.cpp unit that will test a couple of things.
Basically I want to trick the compiler (xCode) into ignoring the real main function for a minute. I could
Rename the main() function inside main.cpp to mmain() temporarily.
Remove the reference to main.cpp in my project temporarily.
Comment out the main() method in main.cpp temporarily.
All these seem pretty clunky. There has to be an easier way. I suspect this is a common thing people do. How do you do it?

Answer 1

Another solution would be to separate the code into multiple files, have most of the logic in one file, have the real main in another and the test main in a third, you compile and link either the first and second or first and third files but never all three together.

Answer 2

Your option 2 is the most common strategie, and from my understanding also the cleanest.
After all, your test application will most likely not share the same command line interface, and that is usually about the only thing which should (of at all) be located in the main function or file.
If your main.cpp contains significantly more than just the entry point, you should immediately start thinking about how to distribute that logic into the modules you already have.

Answer 3

Use a macro.
Option 1: Use a macro to include/exclude entire files:
main.cpp:
#ifdef USE_REAL_MAIN
int main(int argc, char* argv[]) {
...
}
#endif
testMain.cpp
#ifdef USE_TEST_MAIN
int main(int argc, char* argv[]) {
...
}
#ENDIF
build file:
gcc -DUSE_REAL_MAIN
gcc -DUSE_TEST_MAIN
Option 2: Use a command-line macro to rename main:
main.cpp:
int realMain(int argc, char* argv[]) {
...
}
testMain.cpp
int testMain(int argc, char* argv[]) {
...
}
build file:
gcc -DrealMain=main
gcc -DtestMain=main
Note this is probably the least attractive option because it breaks the convention of macros having UPPER_CASE names and means the real entrypoint of your program is non-obvious to someone who hasn't seen the build script. It also means the program simply won't compile (as there's no main function) without your custom build script either.
Option 3: Have a new common main with the #ifdef directives instead:
main.cpp
#include "realMain.h"
#include "testMain.h"
int main(int argc, char* argv[]) {
#ifdef USE_TEST_MAIN
return testMain( argc, argv );
#else
return realMain( argc, argv );
#endif
}
build file:
gcc -DUSE_REAL_MAIN
gcc -DUSE_TEST_MAIN
I think this is my preferred option because it's almost self-documenting and makes it clear to another programmer how to get it to work without needing your custom build script.