Question

I have a c++ program which has many many functions and I have different .cpp files for each of the function. From the main program, I only supply a few parameters and just call the functions. However, the compilation of the full thing takes a lot of time. For each compilation I only change a few parameters in the main program and leave all the functions as it is.
Is there anyway to speed up the compilation.?

Answer 1

You are recompiling unnecessary code. Usually IDEs handle this automatically. Otherwise, it depends on how you compile your code. For example lines like this:

g++ *.cpp

or

g++ -o program a.cpp b.cpp c.cpp

are terribly slow, because on every compilation, you recompile everything.

If you are writing Makefiles, you should carefully write it to avoid recompilation. For example:

.PHONY: all
all: program

program: a.o b.o c.o
    g++ -o $@ $^ $(LDFLAGS)
%.o: %.cpp
    g++ $(CXXFLAGS) -o $@ $<
# other dependencies:
a.o: a.h
b.o: b.h a.h
c.o: c.h

In the above example, changing c.cpp causes compilation of c.cpp and linking of the program. Changing a.h causes compilation of a.o and b.o and linking of the program. That is, on each build, you compile the minimum number of files possible to make the program up-to-date.

Side note: be careful when writing Makefiles. If you miss a dependency, you will may not compile enough files and you may end up getting hard-to-spot segmentation faults (at best). Take a look also at the manual of gcc for -M* options where you can use gcc itself to generate the dependencies and then include the generated output in the Makefile.