openssl/NOTES-ANSI.md

Notes on ANSI C

When building for pure ANSI C (C89/C90), you must configure with at least the following configuration settings:

• no-asm

  There are cases of asm() calls in our C source, which isn't supported in pure ANSI C.

• no-secure-memory

  The secure memory calls aren't supported with ANSI C.

• -D_XOPEN_SOURCE=1

  This macro enables the use of the following types, functions and global variables:

  • timezone

• -D_POSIX_C_SOURCE=200809L

  This macro enables the use of the following types, functions and global variables:

  • ssize_t
  • strdup()

It's arguable that with gcc and clang, all of these issues are removed when defining the macro _DEFAULT_SOURCE. However, that effectively sets the C language level to C99, which isn't ANSI C.