Precompiled header

Optimized type of file in computer programming In computer programming, a precompiled header (PCH) is a (C or C++) header file that is compiled into an intermediate form that is faster to process for the compiler. Usage of precompiled headers may significantly reduce compilation time, especially when applied to large header files, header files that include many other header files, or header files that are included in many translation units. The ideas of precompiled headers were central to the development of C++ modules. Rationale In the C and C++ programming languages, a header file is a file whose text may be automatically included in another source file by the C preprocessor by the use of a preprocessor directive in the source file. Header files can sometimes contain very large amounts of source code (for instance, the header files windows.h and Cocoa/Cocoa.h on Microsoft Windows and OS X, respectively). This is especially true with the advent of large "header" libraries that make extensive use of templates, like Eigen, Boost, and POCO. They are written almost entirely as header files that the user #includes, rather than being linked at runtime. Thus, each time the user compiles