How to recompile source file every time while using cmake 2.8.2 in single build for c++11 and c++98 for shared library creation?

Question

I have a project directory structure of:

Root
  Source
    Common
      MyFolder
      ++ My 3 source files and header 

When I am building

Answer 1

This is sort of counter to how makefiles and cmake usually work.

Most users consider it really important that make performs an incremental build.

The usual way with makefiles is to do make clean which is supposed to remove any binaries and object files that were created.

However, sometimes I write cmake scripts that use globbing over the source directory to assemble the project. (That means, it says "just grab all *.cpp files in the /src folder and make an executable from them".) A makefile cannot check what files in a directory, so the make build will be broken after I add a new file, and make clean won't fix it -- the whole makefile will need to be regenerated by cmake.

Usually what I do is, I write a simple bash script, named rebuild.sh or something,

#!/bin/bash
rm -rf build
mkdir build
cd build
cmake ..
make -j3
./tests

And I put that in the root of my repository, and add /build to my .gitignore. I call that when I want to do a full rebuild -- it nukes the build directory, so its foolproof. When I want an incremental rebuild, I just type make again in the /build directory.

The rebuild.sh script can also serve a double purpose if you use travis-ci for continuous integration.

Answer 2

Most build system assume the compiled objects remain the same within the same pass. To avoid shooting your foot I would suggest telling the build system they were actually different objects, while still compiled from same source files.

I'm not familiar with cmake but this is how you do with make:

For example you have a a.cpp which you want to compile 2 times for different compiler options:

#include <stdio.h>    
int main(int argc, char* argv[]) {
  printf ("Hello %d\n", TOKEN);
  return 0;
}

And the Makefile would looks like:

SRC := $(wildcard *.cpp)
OBJ_1 := $(patsubst %.cpp,%_1.o,$(SRC))
OBJ_2 := $(patsubst %.cpp,%_2.o,$(SRC))

all: pass1 pass2

pass1: $(OBJ_1)
        gcc -o $@ $(OBJ_1) -lstdc++

pass2: $(OBJ_2)
        gcc -o $@ $(OBJ_2) -lstdc++

%_1.o: %.cpp
        gcc -DTOKEN=1 -c $< -o $@
%_2.o: %.cpp
        gcc -DTOKEN=2 -c $< -o $@

clean:
        rm -f $(OBJ_1) $(OBJ_2)

What I do here is generate two different list of object from the same source files, which you can even do the same for dependency(-MMD -MP flags).