Thread: prototypes and multiple modules

if i have 2 source code files, one has function definitions and the other has the code, do the functions need to be prototyped only in the module that uses the function? it compiles fine if i prototype them in both files but i want to know the standard.

Function definitions go in the .h file, and then the actual code (no prototypes) goes in the .c file.

> it compiles fine if i prototype them in both files but i want to know the standard.
You mean the prototypes are in a header file which you include in both files.

Yes, this is the best way to do it.

For a start, if you change the function without changing the header, you'll start to get very important warnings.

thats not what c for dummies chapter 14 is teaching me.

right now in file1.c i have the function prototype and the function usage, and in file2.c i have the function definition.

what youre saying is in file1.c i should have just the function being used, in file2.c i should have the function definition with an #include "header.h", and in header.h i should have the prototype for that function?

Originally posted by Bigbio2002
thats not what c for dummies chapter 14 is teaching me.

right now in file1.c i have the function prototype and the function usage, and in file2.c i have the function definition.

what youre saying is in file1.c i should have just the function being used, in file2.c i should have the function definition with an #include "header.h", and in header.h i should have the prototype for that function?

Yeah. Something like this:

Code:

/* header.h */
#ifndef HEADER_H
#define HEADER_H

void myfunction( void ); /* prototype */

#endif
/* header.h ends */

/* file1.c */
#include "header.h"

int main( void )
{
    myfunction( );

    return 0;
}
/* file1.c ends */

/* file2.c */
#include "header.h"

void myfunction( void )
{
    ...do something...
}
/* file2.c ends */

Now you can compile and link these and it should work just fine. You can use 'myfunction' in file1.c because it is prototyped (by means of the #include statement), so this file knows the general idea of how the function works. (Its prototype; it knows what arguments it takes so it can handle it correctly.)

Quzah.

alot of files to get 1 little thing to work. im trying to make my own module that i can use for other programs i created. it seems useless to create 2 files just for 1 thing. any suggestions?

You need to create two files for your module:
1) The header file prototypes all of the functions you want available for other files. The "interface" as it were.

2) The .c file contains all variable and actual functions themselves. Once this file is finished and compiled, you never have to do anything to it again.

To use your module, all you do then is #include your header file in whatever file you want to use it.

Take my previous example. It illustrates it clearly. The file2.c would be your module. This has all the functions and what not that your module uses. The header is included in whatever file you need to access/use your module from.

Looking again at my example, you'll see that in order for file1.c to be able to use the function in your module, it needed to include the header file for said module.

Quzah.