This intermediate form is known as a precompiled header, and is commonly held in a file named with the extension .pch or similar, such as .gch under the GNU Compiler Collection.
Microsoft Visual C++ (version 6.0 and newer[citation needed]) can precompile any code, not just headers.
[3] pch.h (named stdafx.h before Visual Studio 2017[4]) is a file generated by the Microsoft Visual Studio IDE wizard, that describes both standard system and project specific include files that are used frequently but hardly ever change.
GCC saves precompiled versions of header files using a ".gch" suffix.
[5] The compiler both tokenizes the input source code and performs syntactic and semantic analyses of headers, writing out the compiler's internal generated abstract syntax tree (AST) and symbol table to a precompiled header file.
Thus, the precompiled header can be shared across all project modules, which dramatically reduces the build times.
[8] Compared to a full PCH mechanism, PTH has the advantages of language (and dialect) independence, as lexical analysis is similar for the C-family languages, and architecture independence, as the same stream of tokens can be used when compiling for different target architectures.
In addition, the time to compile scaling linearly with the size, in lexical tokens, of the pretokenized file, which is not necessarily the case for a fully-fledged precompilation mechanism (PCH in clang allows random access).
[9] Clang's pretokenization mechanism includes several minor mechanisms for assisting the pre-processor: caching of file existence and datestamp information, and recording inclusion guards so that guarded code can be quickly skipped over.