Thread: FILE Handling

Hi,

Hopefully a quick one.
I have recently been doing some C Programming again after not doing any for 4-5years.

So, I have gone a bit all out to make a program that does a little bit of everything to refresh my memory.
The function I have issues with is one that closes an open file. It causes everything to crash out.

Function wise I have, menu, openfile, closefile, confirmfile.
I have made it so if I run the program with the argument stuff.txt (as an example) it passes stuff.txt into confirmfile.
This function fopen's the file and points FILE *fp at the file.
FILE *fp is declared at the top and so should be global.
I then use the closefile function to fclose fp.

When I leave the confirmfile function will C automatically close that file, even if I dont declare it?
The error is a double free or corruption error.

Regards,
Steve

Please post some code

Code:

FILE *fp; //This is declared at the very top of program. outside of any functions

int main(int argc, char *argv[])
{
    int x;

	if(argc == 1) //if only 1 entry in array then go to menu
	{
	showMenu(0);
	}
	else //otherwise a filename or argument was passed in, so try to open
	{
	fn[0] = argv[1];
	confirmFile(fn); //pass filename to function confirmFile
	}
return 0;
}

int confirmFile(char *fn[])
{

fp=fopen(fn[0],"w"); //open File, point fp to the filename
showMenu(1); //run menu function, passing 1 to signify that a file was opened on load
}

//I wont show the menu as its by the by, the below is the closeFile function which follows
// on to directly close the file when called.
int closeFile()
{
	//printf("%s\n", fn[0]);
	//printf("%d\n", *fn[0]);
	//printf("%f\n",fp);
	fclose(fp);
	return(0);
}

I think that's the important parts covered, am I making a simple error here?

Code:

void showMenu(int x)
{
	int option; //set variable for menu choice
	char rtn;  //clear screen
	system("clear");

	printf("###       2 - Close File               ###\n");

	printf("What would you like to do?                \n");
	scanf("%d%c",&option,&rtn);

while (option !=4)
{
	switch(option)
	{
		case 1:
		printf("\nOpen File\n");
		break;

		case 2:
		closeFile();
		break;
		
		case 3:
		printf("\nPointer Menu\n");
		break;

		default:
		printf("Error: I am sorry, that option doesn't exist - Please try again\n");
	}
}
}

My thoughts were that if I didnt set that pointer as a global then I wouldnt be able to use it easily between functions. Or should I be passing the pointer through the functions instead?

I assume fn is decrclaed as char *fn[1] or greater?

You should be passing the FILE pointer to (only) the functions that need it.

Code:

void showMenu(int x);
int confirmFile(char *fn[]);
int closeFile();

char *fn[0];
char *file[0];

Sorry, poor effort on the code pasting! This is my prototyping and variable declarations.
since I only want to deal with one filename I kept fn to a size 0

If you only want one filename then (a) why make it an array and (b) if you do make it an array, then you need to specify that you want one entry:

Code:

char *file[1];