How do I get rid of these messages:

warning: implicit declaration of function [function]

I know the answer.

That sounds like a compiler message. If the compile stops right after that, you probably need to install some header files. It's pretty tough to know what's going on with one line from the CC ouput. Usually you would look in config.log for a file that configure is unable to locate.

It seems that your header files have no prototype declared for some of the functions, so the function itself is implicitly treated as the function prototype. It's actually only a warning, and depending on your compilation flags it should compile even so, so it's no reason to panic. Then again, it shouldn't be a big task to add the prototype to one of your headers or at least add on top of the same source file.

Debian

sorry for the necropost, but you just helped me out a great deal! As [part of] a lab for my net security class we are building and using the exploit3.c and exploit4.c files from Aleph One's "Smashing The Stack For Fun And Profit." and were required to get rid of ALL compiler warnings when using the -Wall option.

evidently, stdlib.h doesn't specify prototypes for the contained functions, at least not for putenv() or getenv(). So if you want to get rid of the implicit function declaration warnings, add the prototypes to your source files. this may help someone else in the future

wonderful.