Thread: Program crashes on reading a line from a file

Hi all,

I’m kind of newbie in C programming. I am trying to write a little application which compares 2 text files from the user, compare between them (line by line) and writes in a third file the differences between the 2 first.

I have chosen to use “fgets” command to read the lines, but my program crashes. There are no compilation errors. It fails on the “While”

Can you please take a look?

Code:

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

void main ()
{
	FILE* firstHandle;
	FILE* secondHandle;

	char* firstFileLine=NULL;
	char* secondFileLine=NULL;

	char firstFile[15];
	char secondFile[15];

	//interface

	printf ("\nPlease enter filename of first file: ");
	scanf ("%s",firstFile);
	printf ("\nPlease enter filename of second file: ");
	scanf ("%s",secondFile);

	// open both files
	firstHandle=fopen (firstFile,"rt");
	if (firstHandle==NULL)
	{
		printf ("\nCannot open firstfile: %s\n",firstFile);
		exit(0);
	}

	secondHandle=fopen (secondFile,"rt");
	if (secondHandle==NULL)
	{
		printf ("\nCannot open second file: %s\n",secondFile);
		exit(0);
	}
	
	//let's read the lines until eof of the first given file. 
	while (fgets(firstFileLine, 50, firstHandle)!=NULL)
	{
		//Do the compare stuff here
	}

}

You don't appear to allocate any memory for firstFileLine, which would be your problem.
In fact, you're trying to write to a null pointer in your fgets.

Just use char firstFileLine[50] to allocate the memory.

Thanks, Dweia, looks better now, however, why do I get 2 warnings?

warning C4047: 'function' : 'char *' differs in levels of indirection from 'char *[50]'
warning C4024: 'fgets' : different types for formal and actual parameter 1

Guessing you have

Code:

char * firstFileLine[50];

instead of

Code:

char firstFileLine[50];

But I might not be psychic enough.

Thanks everybody...