Make cmake pass command line variable to compiler

Question

I have following code:

int main() {
#ifdef COMMIT_VERSION
   cout << "app version: " << COMMIT_VERSION << endl;
#endif
}

I would like to invoke cmake such that it passes COMMIT_VERSION variable defined on command line to g++ and thus to my application. E.g. following invocation:

cmake -WHAT_IS_THE_OPTION_NAME COMMIT_VERSION='"Hello Version"'
make
./a.out

produces output

app version: Hello Version

Answer 1

You can use the -D <var>:<type>=<value> option to add a definition within the cmake script (type and value being optional), like so:

cmake -D COMMIT_VERSION='"whatever version here"' ...

Then, inside the script, you can use the add_definitions function to pass the definition to g++:

add_definitions(-DCOMMIT_VERSION=${COMMIT_VERSION})