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1.5.2 C99 features assumed by Gnulib

Although the C99 standard specifies many features, Gnulib code is conservative about using them, partly because Gnulib predates the widespread adoption of C99, and partly because many C99 features are not well-supported in practice. C99 features that are reasonably portable nowadays include:

• A declaration after a statement, or as the first clause in a for statement.
• long long int.
• <stdbool.h>, although Gnulib code no longer uses it directly, preferring plain bool via the stdbool module instead. See stdbool.h.
• <stdint.h>, assuming the stdint module is used. See stdint.h.
• Compound literals and designated initializers.
• Variadic macros.
  Note: The handling of __VA_ARGS__ in MSVC differs from the one in ISO C 99, see https://stackoverflow.com/questions/5134523/. But usually this matters only for macros that decompose __VA_ARGS__.
• static inline functions.
• __func__, assuming the func module is used. See func.
• The restrict qualifier, assuming AC_REQUIRE([AC_C_RESTRICT]) is used. This qualifier is sometimes implemented via a macro, so C++ code that uses Gnulib should avoid using restrict as an identifier.
• Flexible array members (however, see the flexmember module).