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      1 Notes on POSIX
      2 ==============
      3 
      4 There are few instances where OpenSSL requires a POSIX C library, at least
      5 version 1-2008, or compatible enough functionality.
      6 
      7 There are exceptions, though, for platforms that do not have a POSIX
      8 library, or where there are quirks that need working around.  A notable
      9 platform is Windows, where POSIX functionality may be available, but where
     10 the function names are prefixed with an underscore, and where some POSIX
     11 types are not present (such as `ssize_t`).
     12 
     13 Platforms that do have a POSIX library may still not have them accessible
     14 unless the following macros are defined:
     15 
     16     _POSIX_C_SOURCE=200809L
     17     _XOPEN_SOURCE=1
     18 
     19 This is, for example, the case when building with gcc or clang and using the
     20 flag `-ansi`.
     21