how can I find where is the macro or function deifined

Hi; when I used libc I never memorized where each function is located beyond the basics (for example I never knew if strlen is in string.h or ctype.h or strlib.h ) I just check out the functions man pages by man strlen is their such functionality for the kernel where I dont need to memorize the dependencies for example if MODULE_LICENSE is in kernel.h or module.h with out using the internel to google them .