how to find the header file to be included for a library function in linux

Question

Given a function, let's say atoi, how can I find the header file I should include if I want to use this function ? I'm always get puzzled for that issue. If let me treat function like "atoi" as linux c api, I can put my question in another way as : Is a document for linux c api ?

Answer 1

Man pages. Type man atoi (or, in general, man <function>) at your command prompt. It will give you usage information as well as a listing of which headers to include.

Man pages also document programs and commands (find, grep, cd, etc.). Sometimes you may run into a case where a program has the same name as a C function (e.g. write). In that case, you need to direct man to look in the correct section of the manual, section 2 for system calls and section 3 for library functions. You do this by inserting the section number between "man" and the command name: man 2 write. If you do not know whether a given function is a system call or a library function, try both.

You can learn more about manual pages by typing man man.

Answer 2

Is a document for linux c api ?

Certainly. The documentation is available as man pages. Type man <function> in a terminal and enjoy. Which header file you need to include is usually shown at the top.

Answer 3

If you are using ctags and the vim editor and you have set up ctags to scan /usr/include then ctrl-] while you're on the function you want to find takes you to the headerfile!

Answer 4

You can use the following also

whereis <function name> 

It will give the path name for the function. Then open the path using vim editor. Then using the "vim" editor you can see the header file.

Example

> whereis atoi 
   atoi: /usr/share/man/man3/atoi.3.gz

 > vim /usr/share/man/man3/atoi.3.gz

   ----------
   ----------
  .B #include <stdlib.h>