How to load dylib on Mac?

Hi All I'm totally new to C programming on Mac. On other systems I can call dlopen("libkrb5.so", RTLD_NOW) to return a non-NULL pointer to the library. However, on Mac, dlopen("libkrb5.dylib", RTLD_NOW) returns NULL even if I can see the / usr/lib/libkrb5.dylib is right there. What's wrong here? Also, is there a way to write a cross-platform call? Say, dlopen_smart("krb5")? Thanks Max