They are a partially processed version of header files, this speeds up compilation because it doesn't have to repeatedly parse the original header.
## How to use it
The way to do it is to pass the header files you want precompiled to the `target_precompile_headers` command.
Imagine this folder structure:
```
.
├── CMakeLists.txt
└── src
├── header.h
└── main.cpp
1 directory, 3 files
```
Now we create a very basic CMakeLists.txt:
```cmake
cmake_minimum_required(VERSION 3.16)
project(MyProject)
set(HEADER_FILES
src/header.h)
set(SOURCE_FILES
src/main.cpp
${HEADER_FILES}
)
include_directories(src)
add_executable(MyProject ${SOURCE_FILES})
```
Notice we require a minimum cmake version of 3.16, this is due to `target_precompile_headers` being added in that version.
We add the command after the `add_executable` instruction to the private scope.
It's recommended to use the private scope to prevent precompiled headers appearing in an installed target, consumers should decide whether they want to use precompiled headers or not.
