You don't give nearly enough information in your post. For future reference, you should say what you're trying to do, the commands you're using, etc.
I am
assuming that you are compiling
something, and you are getting those errors.
I am
assuming that you are using
gcc to compile the program--meaning that the program is written in C.
I am
assuming that SHA256_Update(), SHA256_Final(), and SHA256_Init() are all part of the same library: libmd (as indicated on
this online man page)
If those
assumptions are incorrect, you need to say which ones are wrong. Otherwise, your problem is likely with your compile command. The errors you posted indicate that gcc cannot link to the function definitions. When you use an external library, you must specifically tell gcc to link with it using the "-l" option. The
typical way to do that is to remove the "lib" from the library name and use what is left with the -l. For example, for libmd:
Code:
gcc -o my_program -lmd my_source.c
