Thread: Examples showing fwrite and fread give back garbage data

This is my first venture into file streams

I've looked over the source-code carefully and couldn't find any differences from the book. Maybe it has something to do with my system?

Here is the console output of my program

Code:

-1208617819
               ¿·±©¿Ç±©¿Û±©¿æ±©¿6␤©¿     -0.05
-1079416719ƒ␤©¿�␤©¿¸┌©¿Þ┌©¿└©¿F└©¿V└©¿£└©¿»└©¿¿└©¿F└©¿V└©¿£└©¿»└©¿     -0.05
-1079415338î└©¿ÿ└©¿┼©¿+┼©¿>┼©¿U┼©¿]┼©¿⎺┼©¿�┼©¿¿>┼©¿U┼©¿]┼©¿⎺┼©¿�┼©¿     -0.05
-1079415137Û┼©¿=⎺©¿]⎺©¿┘⎺©¿┬⎺©¿™⎺©¿²⎺©¿Ö⎺©¿ê⎺©¿¿┬⎺©¿™⎺©¿²⎺©¿Ö⎺©¿ê⎺©¿     -0.05
100                                   0.00
1000                 ¿          598008216632976371697735644702348584536405246902083247220875921706093794716375762404103004004990504111786204800430166155026589905240121409306972824498630058082565445957748647537262486126146850127872.00
3553334                                 0.00
␊┤±␊┼␊@␊┤±␊┼␊-┌▒⎻├⎺⎻:·/␌°␋┌␊⎽$

That last line is actually my console. All alphabetic lower-case characters are screwed up afterwards.




Here is what is used to write to the file

Code:

#include <stdio.h>

struct clientData {
	int acctNum;
	char lastName[ 15 ];
	char firstName[ 10 ];
	double balance;
};


int main()
{
	FILE *cfPtr;
	struct clientData client = { 0, "", "", 0.0 };

	if ( ( cfPtr = fopen( "credit.dat", "r+" ) ) == NULL )
		printf( "File could not be opened.\n" );
	else {
		printf( "Enter account number "
			   " ( 1 to 100, 0 to end input )\n? " );
		scanf( "%d", &client.acctNum );

		while ( client.acctNum != 0 ) {
			printf( "Enter lastname, firstname, balance\n? " );
			fscanf( stdin, "%s%s%lf", client.lastName, client.firstName, &client.balance );
			fseek( cfPtr, ( client.acctNum - 1 ) * sizeof( struct clientData ), SEEK_SET );
			fwrite( &client, sizeof( struct clientData ), 1, cfPtr );
			printf( "Enter account number\n? " );
			scanf( "%d", &client.acctNum );
		}

		fclose( cfPtr );
	}

	return 0;
}

Here is the example to read from the file, the 1st block I posted is this programs output.

Code:

#include <stdio.h>

struct clientData {
	int acctNum;
	char lastName[ 15 ];
	char firstName[ 10 ];
	double balance;
};


int main()
{
	FILE *cfPtr;
	struct clientData client = { 0, "", "", 0.0 };

	if ( ( cfPtr = fopen( "credit.dat", "r" ) ) == NULL )
		printf( "File could not be opened.\n" );
	else {
		printf( "%-6s%-16s%-11s%10s\n", "Acct", "Last Name", "First Name", "Balance" );

		while ( !feof( cfPtr ) ) {
			fread( &client, sizeof( struct clientData ), 1, cfPtr );

			if ( client.acctNum != 0 )
				printf( "%-6d%-16s%-11s%10.2f\n", 
					  client.acctNum, client.lastName, 
					  client.firstName, client.balance );
		}

		fclose( cfPtr );
	}

	return 0;
}

The only things I spotted:

1. I changed "r+" to "a+", otherwise the first program wouldn't create a new file.
2. Because you are using feof incorrectly in the second file, the last record gets printed twice.

But it prints words in the records et cetera just fine.

Interesting

The a+ must have fixed it after I deleted the old "credit.dat". Maybe I got some garbage in the file by trying to view it with the cat command after I created it.