Gcc/10.2.0/gcc/Environment-implementation
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4.2 Environment
The behavior of most of these points are dependent on the implementation of the C library, and are not defined by GCC itself.
The mapping between physical source file multibyte characters and the source character set in translation phase 1 (C90, C99 and C11 5.1.1.2).
See [http://gcc.gnu.org/onlinedocs/cpp/Implementation_002ddefined-behavior.html#Implementation_002ddefined-behavior Implementation-defined behavior] in The C Preprocessor.
