asked on

Compile C function with no Main Block

I am still learning C, and I wanted to know how exactly do I compile a C program containing a function, but that program doesn't have a Main block? I guess what Im trying to say is, make a function in a separate C file that another C program will somehow call? Kind of like a Java class with its main function calling another java class which only contains functions, no main block...

Here is the one C file that I basically am trying to split up into 2 c files, one with the main block and one containing that void hash_pw function...

/*-------------------------------------------------*/

void hash_pw(char * key, int size, char * pw);

main() {

char keyval[] = "POID388631"; /* Input buffer. */
char pwval[11]; /* Query String env variable */

printf("\nit works\n");

strcpy(pwval, keyval);

hash_pw(keyval, strlen(keyval), pwval);

printf("String = %s, Hashed = %s\n", keyval, pwval);
}

void hash_pw( char * key, int size, char * pw ) {

unsigned long n, q;

n=0;

for ( q=0; q<strlen(key); q++ ) {
n = n*1103515245+ (long)key[q];
}

for ( q=0; q<size; q++ ) {
if (n%36 > 9 ) {
*(pw+q) = (char) (n%36+87);
}
else {
*(pw+q) = (char) (n%36+48);
}

n = n*1103515245+12345;
if ((*(pw+q)=='0') || (*(pw+q)=='1') || (*(pw+q)=='l') || (*(pw+q)=='o')) q--;

}

*(pw+size) = (char)0;
return;
}

gj62

Just put it in a different file, create a .h file (say hash.h) that includes the function header, e.g.

void hash_pw(char * key, int size, char * pw);

and include the .h reference in file that has your main(), e.g.

#include <hash.h>

You can then compile it, and include that file in your project (or reference the obj file in your link instructions if not using a development environment like Visual Studio)

posternb

Depending on your compiler, compile with the "compile only" flag. For gcc you'd do:

gcc -c foo.c

and you'd get foo.o containing that code.
You can then link objects together to get an executable like:

gcc foo1.o foo2.o -o foo

to get executable 'foo' (one of the objects need a main function)

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gj62

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gj62

whoops - you need a semicolon in HASH.H after the function declaration...

void hash_pw( char * key, int size, char * pw );

oslicko

ASKER

I seem to be getting this error:

> gcc main.c
Undefined first referenced
symbol in file
hash /var/tmp/cc7UrXv5.o
ld: fatal: Symbol referencing errors. No output written to a.out
collect2: ld returned 1 exit status

Here are my files:
-------------HASH.H--------------

#if !defined( HASH_H )
#define HASH_H

void hash( char * key, int size, char * pw );

#endif

-----------END-HASH.H-------------

--------------HASH.C--------------

void hash( char * key, int size, char * pw ) {

unsigned long n, q;

n=0;

for ( q=0; q<strlen(key); q++ ) {
n = n*1103515245+ (long)key[q];
}

for ( q=0; q<size; q++ ) {
if (n%36 > 9 ) {
*(pw+q) = (char) (n%36+87);
}
else {
*(pw+q) = (char) (n%36+48);
}

n = n*1103515245+12345;
if ((*(pw+q)=='0') || (*(pw+q)=='1') || (*(pw+q)=='l') || (*(pw+q)=='o')) q--;

}

*(pw+size) = (char)0;
return;
}

-----------END-HASH.C-------------

--------------MAIN.C--------------

#include <errno.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include "hash.h"

main() {

char keyval[] = "POID388631";
char pwval[11];
printf("\nit works\n");

strcpy(pwval, keyval);

hash(keyval, strlen(keyval), pwval);

printf("String = %s, Hashed = %s\n", keyval, pwval);

}

-----------END-MAIN.C-------------

Any Ideas?

gj62

Did you compile hash.c and include it in your link?

oslicko

ASKER

I actually forgot to compile hash.c . But now Ive tried again and got the following results:

> gcc -c main.c
> gcc -c hash.c
> gcc hash.o -o main
Undefined first referenced
symbol in file
main /usr/local/gnu/lib/gcc-lib/sparc-sun-solaris2.7/2.95.2/crt1.o
ld: fatal: Symbol referencing errors. No output written to main
collect2: ld returned 1 exit status

I don't think its missing anything , here are the directory contents now:

remus> ls *.c *.o
hash.c hash.o main.c main.o

gj62

Try

gcc hash.o main.o -o main

oslicko

ASKER

Thanks a lot, you've been really helpful!