copying binary files - source and target in c programming

Question

hello guys i made a program which copying binary files, but i have a problem: when im trying to copy the field of the source file to the target file its removing all the field of the target file. how can i solve this problem?

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int  main(int argc, char** argv)
{
    FILE  *source, *target;
    const size_t buffer_size = 8192;
    char buffer[100];
    int strint[100];
    int  a;

    source = fopen(argv[1], "rb");


    if (source != NULL)
    {
        return  -1;
    }

    target = fopen(argv[2], "w+b");

    while (1)
    {
        a = fread(buffer, sizeof(char), buffer_size, source);

        if (!feof(source))
        {
            fwrite(buffer, sizeof(char), buffer_size, target);
        }
        else
        {
            break;
        }

    }

    fclose(target);
    fclose(source);
    system("pause");
    return 0;

}

"when im trying to copy the field of the source file to the target file its removing all the field of the target file." What do you mean? — lost_in_the_source, May 06 '16 at 22:53
Wrong buffer size, no check on `target` Wrong use of `feof()`, wrong size on `fwrite()`. — chux - Reinstate Monica, May 06 '16 at 22:57
Does the target file exist before you run the program? If so, do you want it to have the source file APPENDED to it or do you want it to be OVERWRITTEN by the source file? This "removing the field" language you keep using makes no sense. — Carey Gregory, May 06 '16 at 23:21
Then the program is doing what you want (mostly). Use the code posted by stackptr and it will do exactly what you want. — Carey Gregory, May 06 '16 at 23:26

lost_in_the_source · Answer 1 · 2016-05-07T00:06:05.573

1

You declare buffer_size to be 8192, but you only allocate 100 chars instead of buffer_size. So change the declaration. Also, constants are typically all-caps.
You need to write a bytes onto the destination file, not buffer_size, because the file may not even be buffer_size characters!
Check the return value of fopen; it returns NULL on failure. Check out strerror to print an error reason.
Your loop is wrong. Simply loop while fread returns BUFSIZE (that is, fread reads BUFSIZE characters).
Never use system, because it is highly unportable.

The revised program is

FILE *Fopen(const char *filename, const char *mode)
{
    FILE *fp;

    if ((fp = fopen(filename, mode)) == NULL) {
        strerror("fopen");
        exit(EXIT_FAILURE);
    }
    return fp;
}
int main(int argc, char **argv)
{
    const size_t BUFSIZE = 8192;

    FILE *src, *dest;
    char buf[BUFSIZE];
    size_t n;

    src = Fopen(argv[1], "rb");
    dest = Fopen(argv[2], "w+b");

    while ((n = fread(buf, 1, BUFSIZE, src)) > 0)
        fwrite(buf, 1, n, dest);

    fclose(src);
    fclose(dest);
    return 0;
}

I have not tested the code, so tell me if something is wrong.

edited May 07 '16 at 00:06

answered May 06 '16 at 23:11

lost_in_the_source

10,998
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its removing the field of the target – Daniel Zingerman May 06 '16 at 23:19
2

@DanielZingerman You keep saying it's removing "the field." What do you mean by that? That's completely non-standard terminology nobody understands. – Carey Gregory May 06 '16 at 23:20
i means that there is a binary value in the file , and when im trying to copy its removing the value and the file becoming empty. – Daniel Zingerman May 06 '16 at 23:22
1

The source or destination file? Be more detailed @DanielZingerman Your statements are vague – lost_in_the_source May 06 '16 at 23:27
@stackptr the destination file becoming empty – Daniel Zingerman May 06 '16 at 23:31
@DanielZingerman After you run this program, the destination file will contain **exactly** what the source file contained. If the destination file is empty that's because the source file was empty. – Carey Gregory May 06 '16 at 23:33
@CareyGregory the source file wasnt empty – Daniel Zingerman May 06 '16 at 23:35
1

Seems you actually wanted a ` while ((n = fread(buf, 1, BUFSIZE, src)) > 0)`, no? – Till May 07 '16 at 00:01
1

@Till Good catch. I hope the OP is paying attention because if the source file is smaller than that max buffer size constant it would cause exactly the symptoms he's seeing. The target file would be truncated to empty and nothing would be written to it. – Carey Gregory May 07 '16 at 04:14

xaxxon · Answer 2 · 2016-05-06T23:05:12.747

0

const size_t buffer_size = 8192;
char buffer[100]; // 100 should be buffer_size instead

You're not allocating your buffer size for buffer

Also, you're potentially writing the wrong number of bytes:

        fwrite(buffer, sizeof(char), buffer_size, target);

you should be writing a bytes back so swap out buffer_size with a

edited May 06 '16 at 23:05

answered May 06 '16 at 22:54

xaxxon

19,189
5
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1

what do you mean what do I mean? – xaxxon May 06 '16 at 22:57

score 0 · Answer 3 · answered May 06 '16 at 22:58

Among other issues noted, If by "its removing all the field of the target file" you mean the file target file has all contents removed and you don't want that, you need to read the man page, because it says:

w+

Open for reading and writing. The file is created if it does not exist, otherwise it is truncated. The stream is positioned at the beginning of the file.

Thus,

target = fopen(argv[2], "w+b");

removes all pre-existing data from the target file when you open it.

how can i solve this problem?

Open the file in append mode:

a

Open for appending (writing at end of file). The file is created if it does not exist. The stream is positioned at the end of the file.

like this:

target = fopen(argv[2], "ab");

Only use

target = fopen(argv[2], "a+b");

if you also want to read from target.

copying binary files - source and target in c programming

3 Answers3