please help: fgets() problem

[patkhor]

Hi,

I'm using fgets() to read lines of text file and display them. The fgets() is in an infinite loop. The problem occurs when I remove lines from text file while program is running. The lines count is correct, but the program display the old content of the file up to the new lines count.

This is the output of the program:
Lines count: 12
123
456
789
abc
def
ghi
jkl
mno
pqr
stu
vwx
yz0

<<< At this point, I open the text file and remove "pqr" line, save it, and close the file.

Lines count: 11 // Notice that program has correct line counts
123
456
789
abc
def
ghi
jkl
mno
pqr << "pqr" is still here
stu
vwx
<< but "yz0" is disappear

// One more iteration
Lines count: 11 // Notice that program has correct line counts
123
456
789
abc
def
ghi
jkl
mno
pqr << "pqr" is still here
stu
vwx

I tried to google about using fgets() while file is updated, but no luck. The following is the code.

I'm sorry for my bad English. I'm trying my best to explain the problem.

Any help would be really appreciated.

Thanks in advance,
Pat

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

int main(int argc, char *argv[]) {
	FILE *fp;
	char list[2000][20];
	int count;

	int i, j, k;

	for (;;) {
		count = 0;
		j = 0;

		fp = fopen(argv[1], "r");

		while (fgets(list[i], 20, fp) != NULL) {
			i++;
			count++;
		}

		fclose(fp);

		printf("Lines count: %i\n", count);

		for (i = 0; i < count; i++) {

			for (j = 0; j < strlen(list[i]); j++)
				if ((int)list[i][j] == 13)
					list[i][j] = '\0';


			printf("%s\n", list[i]);
			sleep(1);
		}
		printf("\n");
	}

	exit(0);
}

[Ancient Dragon]

You mean while reading the file there is another program changing it? If that is correct, then all bets are off because the results of your program will be unpredictable. Your program gets the original file probably due to disk cashing -- when the file is opened the program just reads the entire file all at one time then doles it out to your program a little at a time.

[patkhor]

Thank you very much for such a quick reponse. I really appreciate your help.

Yes, you understand correctly. While program is running, I open notepad, remove the line, and save it.

Is there any way to make it work the way I want.

Thank you,
Pat

[Ancient Dragon]

Depends on what you are attempting to do. If you want to see the file contents only after it has been changed by the other program then your only choice is to close the file in your program and reopen it.

If, on the otherhand, you want to see the original contents of the file you have a couple options:

1) After opening the file read the whole thing into memory and work with that.

2) Use some os-specific function to lock the file when it is opened so that other programs can not change it. ON MS-Windows you can use the win32 api fucntion _fsopen()

[patkhor]

Problem solved.

Thank you very much :)