Calculating MD5Sum in C program

[snag49ers]

I'm trying to calculate MD5Sum's inside of a C program but my program tells me 'md5sum undeclared' whenever i try to run the command to calculate. Is there an include file I need or do I need to declare an extern md5sum variable in order to use the command inside the program? Thanks for your help.

[PanGalactic]

Which library are you using? It would help if you showed your code.