File copy routine error!

janet · #1 06-Mar-2004, 02:11

I am writing a program that can duplicate a binary file.
However, the new file will hav extra byte (0xFF) at the end of new file. For example, original file (123.bin) contains 11 Bytes, the generated file (abc.bin) is 12 Bytes, because an extra 0xFF appended at the end of it. How to get rid of it?

123.bin: 6162631198F5BB77660061
abc.bin: 6162631198F5BB77660061FF

CPP / C++ / C Code:

*******source code***************
#include <stdio.h>
#include <stdlib.h>

FILE *inFp;
FILE *outFp;

void main() {
	char inFilename[12];
	char outFilename[12];

	int inChar;

	printf("What is the name of the file you want to back up? ");
	gets(inFilename);

	printf("What is the name of the file ");
	printf("you want to copy %s to? ", inFilename);
	gets(outFilename);

	if ((inFp = fopen(inFilename, "rb")) ==NULL) {
		printf("\n\n*** %s does not exist ***\n", inFilename);
		exit(0);
	}

	if ((outFp = fopen(outFilename, "wb")) == NULL) {
		printf("\n\n*** Error opening %s ***\n", outFilename);
		exit(0);
	}

	printf("\nCopying...\n");

	while (!feof(inFp)) {
		inChar = getc(inFp);
		putc(inChar, outFp);
	}

	printf("\nThe files are copied.\n");

	fclose(inFp);
	fclose(outFp);
}

dsmith · #2 06-Mar-2004, 07:53

Hi Janet. Welcome to GIDForums. I think that your program is outputing EOF. If I remember correctly feof will only be true if the file pointer is sitting on feof. So if you look at your while loop:

CPP / C++ / C Code:

        while (!feof(inFp)) {
		inChar = getc(inFp);
		putc(inChar, outFp);
	}

Your program is getting the end of file, storing it into inChar, writing it out and then checking for the end of file. I would fix this by adding a quick if statement like so:

CPP / C++ / C Code:

while( !feof(inFp) ){
    if( (inChar = getc(inFp) ) != EOF)
          putc(inChar, outFp);
}

See if that fixes it.

Cheers,
d

WaltP · #3 06-Mar-2004, 12:03

Quote:

Originally Posted by dsmith

Hi Janet. Welcome to GIDForums. I think that your program is outputing EOF. If I remember correctly feof will only be true if the file pointer is sitting on feof. So if you look at your while loop:

CPP / C++ / C Code:

        while (!feof(inFp)) {
		inChar = getc(inFp);
		putc(inChar, outFp);
	}

Your program is getting the end of file, storing it into inChar, writing it out and then checking for the end of file. I would fix this by adding a quick if statement like so:

CPP / C++ / C Code:

while( !feof(inFp) ){
    if( (inChar = getc(inFp) ) != EOF)
          putc(inChar, outFp);
}

See if that fixes it.

Cheers,
d

Actually, you should not used feof() to control a loop. Instead change your loop to:

CPP / C++ / C Code:

while ((inChar = getc(inFp)) != EOF)
{
    putc(inChar, outFp);
}

Also, do NOT use gets(). It has a tendancy to make your program explode. Change the gets(inFilename) to

CPP / C++ / C Code:

fgets(inFilename, 12, stdin);
i = strlen(inFilename)-1;
if (inFilename[i] == '\n') inFilename[i] = '\0'; //  remove the trailing newline

The problem with gets() is if you enter ABCDEFGHIJKLMNOPQRSTUVWXYZ.FILETYPE as the filename, the 1st 12 characters will be loaded into the variable, the characters after those 12 get loaded into the bytes following -- destroying other variable contents and possibly writing to space not available to the program. The program then crashes. So never use gets(). It's not worth the headaches.

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