Thread: file processing - strange behavior

This code works, opens file "myfile.txt" for reading and writing and writes a-z characters in the file.

Code:

#include <stdio.h>
#include <stdlib.h>
int main ( void )
{
	int c;
	FILE * fp;
	fp = fopen ( "myfile.txt", "r+" );
	for ( c = 'a'; c <= 'z'; c++ )
    	putc ( c, fp );
	/*while ( ( c = getc ( fp ) ) != EOF )
		putchar ( c );*/
	fclose ( fp );
    return 0;
}

This code also works ( reads characters from the file )

Code:

#include <stdio.h>
#include <stdlib.h>
int main ( void )
{
	int c;
	FILE * fp;
	fp = fopen ( "myfile.txt", "r+" );
	/*for ( c = 'a'; c <= 'z'; c++ )
    	putc ( c, fp );*/
	while ( ( c = getc ( fp ) ) != EOF )
		putchar ( c );
	fclose ( fp );
    return 0;
}

But when I uncomment all code (code for writing characters and reading characters ) I get garbage characters both in my file and console window.
Something like this in console window:
═══════════════════════════════════
═══════════════════════════════════
═══════════════════════════════════
═══════════════════════════════════
═══════════════════════════════════
═══════════════════════════════════
═══════════════════════════════════
═══════════════════════════════════
═══════════════════════════════════...

and like this in the file:

abcdefghijklmnopqrstuvwxyzÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ ÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ
ÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ ÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ...

This is the code that should only write characters a-z in the file and than read them in console window, but it doesn't work. Why?

Code:

#include <stdio.h>
#include <stdlib.h>
int main ( void )
{
	int c;
	FILE * fp;
	fp = fopen ( "myfile.txt", "r+" );
	for ( c = 'a'; c <= 'z'; c++ )
    	putc ( c, fp );
	while ( ( c = getc ( fp ) ) != EOF )
		putchar ( c );
	fclose ( fp );
    return 0;
}

You have to go back to the beginning of the file in order to read the things that you just wrote to it. Check out fseek: fseek - C++ Reference

Code:

fseek(fp, 0, SEEK_SET);

Hello,

Code:

int main ( void )
{
	int c;
	FILE * fp;
	fp = fopen ( "MyFile.txt", "r+" );
	if(fp==NULL)
	{
	  printf("Unable to open the file");
	  exit(0);
	}
	for ( c = 'a'; c <= 'z'; c++ )
    	putc ( c, fp );  //fp will be pointing to last character

              fseek(fp, 0, SEEK_SET); //Reset it to beginning

	while ( ( c = getc ( fp ) ) != EOF ) //Read from 'a'
		putchar ( c );
	fclose ( fp );
    return 0;
}

Hope you understood

Regards,
Siddu

You could also use:

Code:

rewind(fp);

In place of fseek().