Eof??

Hi its me the student again.

This time i read a file but the machine cannot tell if the end of the file has been reached.

i am using


FILE *fp /* pointing to a stream */


while(fp!= EOF)
{
do so and so
}

When i open the stream which is a text file, the last line read from another file is repeated forever, if i dont user break the program.

Please help, thank you Ganonshin. Bye.

To test a file to see if it's already read to or past EOF, you can use 'feof', which is not the preferred method.

A better method is to test the return value of your read function. Check the return value of fgetc, fread, fscanf, or whatever it is you're using to read.

Quzah.

Hi Quzah.

I am using fscanf to read the file - how do i check the return value and when i have the value what do i do with it??

Hope you respond.

Ganonshin, bye for know.

From Salem's post in the C++ Forum

Code:

void good ( char *in, char *out ) {
    FILE *fin = fopen( in, "r" );
    FILE *fout= fopen( out,"w" );
    int ch;
    while ( (ch=fgetc(fin)) != EOF ) {
        fputc(ch,fout);
    }
    fclose(fin);
    fclose(fout);
}

Thanks Azuth, b ut i dont really understand it.

Thanks anyway Ganonshin.

The key to testing for eof is in this loop

Code:

while ( (ch=fgetc(fin)) != EOF ) {
        fputc(ch,fout);
}

I haven't used fscanf much, but it appears to have a number of limitations that fgetc does not. If you switched to fgetc it then becomes a case of how you deal with the data once read from the file.

What is in the text file? Is it delimted? What do you do with the text when you read it in?

The basic format is this

Code:

while ( fscanf( ... ) != EOF) {
  /* Do something with it..or not */
}

Any input function can replace the scanf() functions, such as fgetc(), fgets(), etc.

But as Salem often says do not do this

Code:

while (!feof(fileptr)){
  /*blah blah*/
}

Because it reads the last line twice.

kwigibo

>But as Salem often says do not do this...
and quite rightly too. Here's an example of bad coding.

Code:

#include <stdio.h>
#define FILENAME "text.txt"
int main(void)
{
	char buffer[1024];
	FILE *fileptr;
	int lines = 0;
	
	if ((fileptr = fopen(FILENAME, "r")) == NULL)
	{
		perror(FILENAME);
		return (1);
	}
	
	while (!feof(fileptr))
	{
		fgets(buffer, 1024, fileptr);
		lines++;
		printf ("Line %d of the file is %s", lines, buffer);
	}
	
	fclose(fileptr);
	
	return (0);
}

Create a text file called text.txt with say 5 lines of data in it. You'll find that you actually get 6 lines of output. Well, at least that's what happens under some compilers. I have found that some do handle it differently. Therefore it is best not to use code like this.

What I found that worked (someone can tell me if this sounds incorrect), I get a char from the input file. Then I test for EOF using feof. Then if the file is not at the end I put the char back to the input stream.

- Sean

Hi everyone, I cant remeber who sugested to get the return value but it worked, a big cheers if you know who you are.

Thanks from Ganonshin.