Initializing and uninitializing OpenSSL library
As of version 1.1.0, the OpenSSL library does not require explicit initialization and uninitialization. The library will automatically initialize and uninitialize.
However, it is still possible to initialize OpenSSL explicitly if some non-standard initialization is needed. It is also possible to uninitialize explicitly, but it is discouraged, especially in multithreaded programs or if OpenSSL may be used by both the program and another library in the same process. Note that after uninitialization, it is not possible to initialize OpenSSL again.
Explicit initialization is done by calling the OPENSSL_init_ssl() function. Explicit uninitialization is done by calling the OPENSSL_cleanup() function.
Older versions of OpenSSL, below 1.1.0, will not initialize automatically. If you need to use an old OpenSSL version, you have to initialize it explicitly, using now-deprecated functions called SSL_library_init() and EVP_cleanup().