How to use OpenSSL's SHA256 functions

Solution 1:

You make a very common beginners mistake... Putting the libraries you link with in the wrong place on the command line when you build.

Dependencies are reversed on the command line, so something that depends on something else should actually be put before what it depends on on the command line.

In your example, you have a source file main.cpp that depends on some set of libraries, then the source file should be before the libraries it depend on:

$ g++ -o main main.cpp -lssl -lcrypto

To be safe, always put libraries last, after any source or object files listed on the command line.