Creating your own header file in C - c

Question

Can anyone explain how to create a header file in C with a simple example from beginning to end.

Answer 1

foo.h
#ifndef FOO_H_ /* Include guard */
#define FOO_H_
int foo(int x); /* An example function declaration */
#endif // FOO_H_
foo.c
#include "foo.h" /* Include the header (not strictly necessary here) */
int foo(int x) /* Function definition */
{
return x + 5;
}
main.c
#include <stdio.h>
#include "foo.h" /* Include the header here, to obtain the function declaration */
int main(void)
{
int y = foo(3); /* Use the function here */
printf("%d\n", y);
return 0;
}
To compile using GCC
gcc -o my_app main.c foo.c

Answer 2

#ifndef MY_HEADER_H
# define MY_HEADER_H
//put your function headers here
#endif
MY_HEADER_H serves as a double-inclusion guard.
For the function declaration, you only need to define the signature, that is, without parameter names, like this:
int foo(char*);
If you really want to, you can also include the parameter's identifier, but it's not necessary because the identifier would only be used in a function's body (implementation), which in case of a header (parameter signature), it's missing.
This declares the function foo which accepts a char* and returns an int.
In your source file, you would have:
#include "my_header.h"
int foo(char* name) {
//do stuff
return 0;
}

Answer 3

myfile.h
#ifndef _myfile_h
#define _myfile_h
void function();
#endif
myfile.c
#include "myfile.h"
void function() {
}

Answer 4

header files contain prototypes for functions you define in a .c or .cpp/.cxx file (depending if you're using c or c++). You want to place #ifndef/#defines around your .h code so that if you include the same .h twice in different parts of your programs, the prototypes are only included once.
client.h
#ifndef CLIENT_H
#define CLIENT_H
short socketConnect(char *host,unsigned short port,char *sendbuf,char *recievebuf, long rbufsize);
#endif /** CLIENT_H */
Then you'd implement the .h in a .c file like so:
client.c
#include "client.h"
short socketConnect(char *host,unsigned short port,char *sendbuf,char *recievebuf, long rbufsize) {
short ret = -1;
//some implementation here
return ret;
}