c++ accessing functions from another file

Question

I'm learning c++ and having a bit of trouble with how you share methods with different files and or classes.

if I make a function called increment(int a){a++; return a;}

and have it defined in a.cpp how would I call it in main.cpp? Any help is appreciated, thanks.

http://stackoverflow.com/questions/11943457/correctly-using-header-files — Kamouth, Jun 05 '13 at 12:49
@BasileStarynkevitch +1. There is even a [list of good books](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list) here on SO. — Angew is no longer proud of SO, Jun 05 '13 at 13:09
Also enable all warnings and debugging info. On Linux, compile with `g++ -Wall -g` and learn to use the `gdb` debugger. — Basile Starynkevitch, Jun 05 '13 at 17:29

score 6 · Answer 1 · answered Jun 05 '13 at 12:55

Put int increment(int a); at the top of main.cpp.
Compile both files into object files (with g++, you can use the -c option for that).
Link both files together (with g++, just say g++ main.o increment.o -o increment.exe).

Now, declaring int increment(int a); in every cpp-file that uses this function is very cumbersome. That's why a shortcut exists:

Problem with this method is, that increment.h might be included multiple times into a single cpp-file. This is where include guards come in.

score 0 · Answer 2 · answered Jun 05 '13 at 12:49

0

Use declaration

 int increment(int a);

in the file that wants to call. Usually you #include those declarations form a common file (header) shared by many .cpp files.

answered Jun 05 '13 at 12:49

Balog Pal

2 Answers2