Here is a little anecdote about bringing old source code using OpenSSL to recent versions…

foo.c:47:11: warning: ‘ERR_remove_state’ is deprecated [-Wdeprecated-declarations]
      ERR_remove_state(0);
      ^~~~~~~~~~~~~~~~
...
/usr/include/openssl/err.h:248:1: note: declared here
DEPRECATEDIN_1_0_0(void ERR_remove_state(unsigned long pid))
^

Hm, okay, ERR_remove_state is deprecated. Let me check the OpenSSL man pages…

ERR_remove_state is deprecated and has been replaced by ERR_remove_thread_state.

Ah, well, that seems easy to replace with ERR_remove_thread_state!

*hackhackhack*

foo.c:47:11: warning: ‘ERR_remove_thread_state’ is deprecated [-Wdeprecated-declarations]
      ERR_remove_thread_state(NULL);
      ^~~~~~~~~~~~~~~~~~~~~~~
 ...
 /usr/include/openssl/err.h:247:1: note: declared here
  DEPRECATEDIN_1_1_0(void ERR_remove_thread_state(void *))
  ^

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