File Copying - Random chars at the end

**Govalant** · 05-26-2007

Hi, well I was trying to write a simple, small program that copy files.

The code is this:

Code:

#include <stdio.h>

int main(int argc, char** argv)
{
    if (argc < 3)
    {
        printf("Not enought arguments supplied.");
        exit(1);
    }

    FILE* f1;
    FILE* f2;

    f1=fopen(argv[1],"r");

    if(f1==NULL)
    {
        printf("Source file does not exist.");
        exit(1);
    }

    f2=fopen(argv[2],"w");

    while(!feof(f1))
    {
        putc(getc(f1),f2);
    }

    fclose(f1);
    fclose(f2);

    return 0;


}

But when I copy the files some random chars get added at the end of the destination file.

Anyone knows what's wrong?

Oh, another question: What's the library for exit()?

**MacGyver** · 05-26-2007

Check the FAQ on the problem with using feof() to control a loop. The basic idea is that you'll call feof(), and EOF will not be reached, so it will return false. You enter the loop, call getc(), and it returns EOF. Now feof() will return true, but that's too late because you're printing the representation of EOF into the file.

Code:

while(!feof(f1))
{
    putc(getc(f1),f2);
}

Change to something like this:

Code:

int c;
...
while((c = getc(f1)) != EOF)
{
    putc(c,f2);
}

exit() is from stdlib.h btw.

**Salem** · 05-26-2007

Yes, it's because you're using feof() to control the while loop.
This is explained in the FAQ.

**zacs7** · 05-26-2007

Don't use feof() to control loops see the FAQ

consider,

Code:

int c;

while((c = getc(f1)) != EOF)
    putc(c, f2);

edit: too slow

**Govalant** · 05-26-2007

Thanks

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