Question

Is it a good idea to use #include "randombytes.cpp" instead of randombytes.h in my project (where randombytes.cpp is a file in my projects source code directory) for runtime speed reasons? randombytes.cpp would look like this:

#ifndef RANDOMBYTES_INCLUDED
#define RANDOMBYTES_INCLUDED

/* include native headers here */

unsigned char *fetch_random_bytes(int amount);

/* include other parts of my project here if necessary */

unsigned char *fetch_random_bytes(int amount) {
  // do stuff
}

#endif

This should also work for files requiring each other and so on, right? Can you think of any cases in which this won’t work or I won’t get the optimization benefit?

Answer 1

This practice is called “Unity Build” (google it) and is generally not a good idea for anything but trivial projects since you will need to recompile the entire project every time you make a single change, which can mean minutes of waiting every time you fix a tiny error.

As for runtime performance, the difference in speed is not very different from compiling with Link Time Optimizations on.