There are also some options that define macros implicitly, like -O and -Wdeprecated the same rule applies to macros defined this way. The -D option is one way to define a macro before a precompiled header is included using a #define can also do it. * Any macros defined before the precompiled header is included must either be defined in the same way as when the precompiled header was generated, or must not affect the precompiled header, which usually means that they don't appear in the precompiled header at all. The easiest way to guarantee this is to use the same compiler binary for creating and using precompiled headers. * The precompiled header file must be produced by the same compiler version and configuration as the current compilation is using. You can't use a C precompiled header for a C++ compilation. * The precompiled header file must be produced for the same language as the current compilation.

You can have preprocessor directives before a precompiled header you can even include a precompiled header from inside another header, so long as there are no C tokens before the #include. * A precompiled header can't be used once the first C token is seen. * Only one precompiled header can be used in a particular compilation. aders.htmlĪ precompiled header file can be used only when these conditions apply:

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