Create a static library in C using CMAKE - c

Question

The structure of my project is like this:
DriverFolder
Src
"myDriver.c"
Inc
"myDriver.h"
ApplicationFolder
Src
"myApplication.c"
Inc
"myApplication.h"
The "myApplication.c" source file contains this code:
#include "myApplication.h"
#include "myDriver.h" // Driver included from DriverFolder
uint8_t myFunction(void)
{
uint8_t fooValue = getValueFromDriver(); // A function in myDriver.h
return fooValue;
}
The header file "myApplication.h" contains macros and prototypes
#ifndef LIBRARY_MYAPPLICATION_H
#define LIBRARY_MYAPPLICATION_H
uint8_t myFunction(void);
#endif
I want to create a static library (.lib) using CMAKE. My goal is to include this library in another project. The other project looks like this:
#include "myApplication.h"
int main(void)
{
printf("%d", myFunction());
return 0;
}
I would like to know how to prepare the CMakeLists.txt. For now, this is what I have:
cmake_minimum_required(VERSION 3.0.0)
project(MYAPPLICATION VERSION 0.1.0)
add_library(MYAPPLICATION STATIC myDriver.c myApplication.c)
How to add include paths (DriverFolder/Inc and ApplicationFolder/Inc ?
What else should I add/modify in CMakeLists.txt in order to generate the library?

Answer 1

A static library is really nothing more than an archive of object files. As such they don't contain header files in themselves. Instead when you distribute or install the library, you need to also distribute or install the public header files. What you don't need is to list the header files when creating the actual library, so you don't need to add them at all.
Also, if the object files created from the listed source files (myDriver.c and myApplication.c) are all you need for the actual static library, then the shown CMakeLists.txt file is all that's needed to generate the library.
As mentioned in a comment, there are actually a couple of things missing to help build the object files needed for the library. The creation of the static library itself from the object files is fine.
The problem is that your header-files are in a non-standard location and that the compilers pre-processor will not be able to find the ones not in the same directory as the source file.
That means you have to tell CMake to add flags that tells the compiler where the header files are located. You can do this with the target_include_directories command.
And you also need to list the full (relative) path to the source file.
So the CMakeLists.txt file should probably look something like this:
cmake_minimum_required(VERSION 3.0.0)
project(MYAPPLICATION VERSION 0.1.0)
add_library(MYAPPLICATION STATIC DriverFolder/Src/myDriver.c ApplicationFolder/Src/myApplication.c)
# Tell CMake where the header files are located
target_include_directories(MYAPPLICATION PUBLIC DriverFolder/Inc ApplicationFolder/Inc)
Note that this only makes it possible to build the source files into object files. It will not include the header files inside the library, or automatically install them anywhere.