Thread: Passing pointers to functions in seperate source files

Hi Everybody,

I'm brand new here and this is my first post...

I think my question is straight forward - I'm fairly new to C but I have to this point written many small useless programs that use structs, pointers and functions.

I have no problem passing the address of a struct array to a function and I have no issues getting the functions to perform their specific tasks to the struct arrays - as long as all my code is in the same source file.

This is my problem. Early in my introduction to C I got in the habit of keeping the source file containing main() small, and having separate source files containing like functions.

I was having little to no difficulty maintaining this until I started to pass pointers around. Now I can't seem to compile without error unless all my code is in the same source file.

Any ideas on what I might be doing wrong? Is this in fact bad practice to be using separate source files?

Here's an example.. this program compiles and runs as I intended it to. But if I put the functions newDriver() and displayDriver in a seperate source file I cannot get the program running to save my life.

Code:

#include <stdio.h>
#include <stdlib.h>

struct person
{
	char lastName[20];
	char firstName[20];
	char age[4];
	char position[20];
};

typedef struct person person;

int counter = 0;
int displayCounter;

person *empPtr;

newDriver(person *empPtr)
{
	fputs("\n*New Driver Entry\n", stdout);
	fputs("Enter driver last Name: ", stdout);
	fgets(empPtr[counter].lastName, 20, stdin);
	fflush(stdin);
	empPtr[counter].lastName[strlen(empPtr[counter].lastName) - 1] = '\0';

	fputs("Enter driver first Name: ", stdout);
	fgets(empPtr[counter].firstName, 20, stdin);
	fflush(stdin);
	empPtr[counter].firstName[strlen(empPtr[counter].firstName) - 1] = '\0';

	fputs("Enter driver age: ", stdout);
	fgets(empPtr[counter].age, 4, stdin);
	fflush(stdin);
	empPtr[counter].age[strlen(empPtr[counter].age) - 1] = '\0';

	fputs("Enter driver position: ", stdout);
	fgets(empPtr[counter].position, 20, stdin);
	fflush(stdin);
	empPtr[counter].position[strlen(empPtr[counter].position) - 1] = '\0';
}

displayDriver(person *empPtr)
{
	fputs("\n*Display Driver Entries\n", stdout);
	
	for(displayCounter =0; displayCounter < counter; displayCounter++)
	{
		printf("%s, %s\t\t\t%s\t%s\n", empPtr[displayCounter].lastName,
						empPtr[displayCounter].firstName, empPtr[displayCounter].age,
							empPtr[displayCounter].position);
	}	
}

int main(void)
{
	
	char userSay[10];

	
	empPtr = malloc(20 * sizeof(person));
	
	if(empPtr == NULL)
	{		
		printf("There was a memory allocation problem.\n");
		exit(1);
	}
	
	fputs("*** Taxi Employee Database ***\n\n", stdout);

	do
	{
		fputs("--->", stdout);
		fgets(userSay, 10, stdin);
		fflush(stdin);
		userSay[strlen(userSay) - 1] = '\0';
		
		if(!strcmp(userSay, "quit"))
		{
			fputs("\nGoodbye!\n", stdout);
		}
		else if(!strcmp(userSay, "new"))
		{
			newDriver(empPtr);
			counter++;
		}
		else if(!strcmp(userSay, "display"))
		{
			displayDriver(empPtr);
		}
		else
		{
			fputs("Unknown Entry\n", stdout);
		}		

	}while(strcmp(userSay, "quit"));

	free(empPtr);

	exit(0);
}