How do I use the C preprocessor to make a substitution with an environment variable

Question

In the code below, I would like the value of THE_VERSION_STRING to be taken from the value of the environment variable MY_VERSION at compile time

Answer 1

If I recall correctly, you can use the command line parameter -D with gcc to #define a value at compile time.

i.e.:

$ gcc file.c -o file -D"THE_VERSION_STRING=${THE_VERSION_STRING}"