Thread: File check

hey

hope you guys can help me! I know what I want to do in words but am finding difficulty in putting it in to code.

Basically, when my program starts I want it to check whether the file it uses has any data in it. If it does not, then I want to initialise a certain element of a struct. If it does, then I don't!

Problem I have is how do I check whether the file has any data in it?

Thanks

thanks for your replies

So, how would I set up a test condition using fseek to see if there was anything in the file?

would I seek the beginning of the file in question and then fscanf to see if there was anything there????

IF the file FNAME has just been created. Should not the size be equal to zero?

Code:

int file_check()
{
	FILE *fptr;
	int size;

	fptr = fopen(FNAME, "rb");
	fseek(fptr, 0, SEEK_END);
	size = ftell(fptr);

	return size;
}

please help

No it doesn't! :-(

Why does it not? :-S

Hey! this is the part of my code which uses this function. Basically, the first time the user, uses the program I want the strcut flag to be set to zero.

Code:

main()
{
	pass customers[ROW][LABEL];
	int i, j;
	long empty;

	clear_screen();
	atexit(thank_you);
	read_file(customers);
	empty = file_check();
	if(empty == 0) //If there is no data in the file loaded then we should initialise flag to zero for all structs.
	{
		for(i = 0; i < ROW; i++) 
			for(j = 0; j < LABEL; j++)
			customers[i][j].flag = 0;
	}
}

Code:

void read_file(pass cust[][LABEL])
{
	FILE* fptr;

	fptr = fopen(FNAME, "rb");
	if(fptr == NULL)
	{
		fprintf(stderr, "Could not open %s - %s\n", FNAME, sys_errlist[errno]);
		if(yesno("Do you wish to create this file?"))
		{
			write_file(cust);
			fptr = fopen(FNAME, "rb");
		}
		else
			exit(1);
	}
	
	fread(cust, sizeof(cust), 1, fptr);
	fclose(fptr);
}

Code:

void write_file(pass cust[][LABEL])
{
	FILE *fptr;

	fptr = fopen(FNAME, "wb");
	
	if(fptr == NULL)
		{
			fprintf(stderr, "Could not open %s - %s\n", FNAME, sys_errlist[errno]);
			exit(1);
		}
	
	fwrite(cust, sizeof(cust), 1, fptr);
	fclose(fptr);
}

Code:

long file_check()
{
	FILE *fptr;
	int size;

	fptr = fopen(FNAME, "rb");
	fseek(fptr, 0, SEEK_END);
	size = ftell(fptr);

	return size;
}

Thanks for your help! Its much appreciated!

Surely, if I've just created any file it should be 0 bytes?

Code:

struct	passenger
{
int flag;  //Use as a boolean - 1 if seat taken, 0 if not taken
char *first;
char *last;
};

typedef struct passenger pass;

b.t.w - This is the structure - sorry!

So the file never gets created???



Also yesno function - returns a 1 if user puts yes and a zero if user puts no.

So what you're saying is (assuming the user wants to create the file) that the file will never be created. But when I run the program the file does get created but it is 1KB in size. This is confusing :-S

AHA!!! I have found what the problem is. I can fix it but the way I'm thinking won't look pretty. So I'm here to see if you "experts" know any smarter ways.

Code:

#define ROW 7
#define LABEL 2


struct	passenger
{
int flag;  //Use as a boolean - 1 if seat taken, 0 if not taken
char *first;
char *last;
};

Code:

main()
{
	pass customers[ROW][LABEL];
	int i, j;

	atexit(thank_you);
	if(read_file(customers))
	{
		for(i = 0; i < ROW; i++) 
			for(j = 0; j < LABEL; j++)
			customers[i][j].flag = 0;
		write_file(customers);
	}
}

Code:

int read_file(pass cust[][LABEL])
{
	FILE* fptr;
	int new_file = 0;
	

	fptr = fopen(FNAME, "rb");
	if(fptr == NULL)
	{
		fprintf(stderr, "Could not open %s - %s\n", FNAME, sys_errlist[errno]);
		if(yesno("Do you wish to create this file?"))
		{
			write_file(cust);
			fptr = fopen(FNAME, "rb");
			new_file = 1;
		}
		else
			exit(1);
	}
	
	fread(cust, sizeof(cust), 1, fptr);
	fclose(fptr);
	
	return new_file;	
}

Code:

void write_file(pass cust[][LABEL])
{
	FILE *fptr;

	fptr = fopen(FNAME, "wb");
	
	if(fptr == NULL)
		{
			fprintf(stderr, "Could not open %s - %s\n", FNAME, sys_errlist[errno]);
			exit(1);
		}

	printf("In write file size of cust is %d", sizeof(cust));
	getchar();
	fflush(stdin);
	
	fwrite(cust, sizeof(cust), 1, fptr);
	fclose(fptr);
}

Here's the problem!! The struct passed into the different functions is the pointer. So If I take the sizeof - it will be 4 bytes. How do I get the sizeof the original array of structures using the pointer (cust)?


Thanks

without taking the name arrays into consideration
sizeof(*cust) * ROWS

if you want a size that takes into consideration extra memory allocated to the names, thats gonna be more difficult