Can't get fwrite to work properly

Question

I'm trying to write a program that is able to open a text file and split it so I can save it in two new ones to save files faster. But with the code I have now I'm not able to print the chars that I pick from the orignal file to the new ones.

In my text file I have the text "Dutch people are tall".

In my new files I want to get: File 1: Dthpol r tl File 2: uc epeaeal

This is the code I have got so far:

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

int main()
{
    char cUsb1;
    char cUsb2;
    char str[128];

    FILE *ptr_readfile;
    FILE *ptr_usb1;
    FILE *ptr_usb2;

    ptr_readfile = fopen("Dutch People.txt","r"); // open readfile

    while(ptr_readfile != NULL) // keep running while readfile != null
    {
        if (ptr_readfile != EOF) // keep running while readfile != eof
        {
            cUsb1 = fgetc(ptr_readfile); // to get a char out of the readfile
            ptr_usb1 = fopen("USB1.txt", "w"); // create and open USB1 file
            fwrite(cUsb1 , str , str , ptr_usb1); //writing get c to file

            cUsb2 = fgetc(ptr_readfile); // to get a char out of the readfile
            ptr_usb2 = fopen("USB2.txt", "w"); // create and open USB2 file
            fwrite(cUsb2 , str , str, ptr_usb2); //writing get c to file

        fclose(ptr_usb1); // closing the file
        fclose(ptr_usb2); // closing the file
        }
    break;  // to stop the while loop
    fclose(ptr_readfile); // closing the file
    }

    return 0;
}

`Dthpol r tl` might `Dthpol r al`, `uc epeaeal` --> `uc epeaetl` — BLUEPIXY, Apr 21 '15 at 14:28
First, I think that it is necessary to read the tutorial of basic input and output. — BLUEPIXY, Apr 21 '15 at 14:31
Your program is totally wrong. You should: 1) fopen all three files. 2) read 1 char from "Dutch People.txt", and write it to "USB1.txt", read 1 char from "Dutch People.txt", and write it to "USB2.txt". Repeat 2) until you read an EOF. 3) fclose all files. And remind, `fgetc` returns an `int` and not a `char`. — Jabberwocky, Apr 21 '15 at 14:38

Jack Whitham · Accepted Answer · 2015-04-21T14:58:55.543

0

Many things are not quite right. You need to look carefully through the warnings reported by the compiler - enable all warnings if possible (e.g. "-Wall") - and resolve them all. Then single-step through your program with a debugger until it does something you didn't expect.

As a starting point, instead of:

 fwrite(cUsb1 , str , str , ptr_usb1);

you might mean

 fwrite(&cUsb1 , 1 , 1 , ptr_usb1);

There should be a warning for that line to tell you that you shouldn't try to pass cUsb1 (a char) as the first parameter of fwrite, as that parameter expects a pointer, i.e. an address of something. Use &cUsb1 to mean "the address of cUsb1".

edited Apr 21 '15 at 14:58

answered Apr 21 '15 at 14:38

Jack Whitham

609
4
9

`feof()` doesn't return `true` when you have reached the end of the file. It returns `true` after you attempt to read beyond the end of a file. http://stackoverflow.com/questions/5431941/why-is-while-feof-file-always-wrong – Weather Vane Apr 21 '15 at 14:46
You mean, it returns nonzero :). But fair enough, I picked another example. – Jack Whitham Apr 21 '15 at 15:02
Non-zero *is* true. C does not have an explicit value for `true`. – Weather Vane Apr 21 '15 at 15:05

Selçuk Cihan · Answer 2 · 2015-04-22T06:02:15.217

You can use fputc for writing one character at a time. Also the while loop is not needed.

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

int main()
{
    int c;

    int i = 0;

    FILE *ptr_readfile = NULL;
    FILE *ptr_usb1 = NULL;
    FILE *ptr_usb2 = NULL;

    ptr_readfile = fopen("Dutch People.txt", "r"); // open readfile
    if (ptr_readfile != NULL) {
        ptr_usb1 = fopen("USB1.txt", "w"); // create and open USB1 file
        ptr_usb2 = fopen("USB2.txt", "w"); // create and open USB2 file
        if (ptr_usb1 != NULL && ptr_usb2 != NULL) {
            while ((c = fgetc(ptr_readfile)) != EOF) {
                if (i % 2 == 0) {
                    fputc(c, ptr_usb1);
                }
                else {
                    fputc(c, ptr_usb2);
                }
                i++;
            }
        }
        fclose(ptr_readfile); // closing the file
    }
    if (ptr_usb1 != NULL) {
        fclose(ptr_usb1);
    }
    if (ptr_usb2 != NULL) {
        fclose(ptr_usb2);
    }

    return 0;
}

`char c` should be `int c` to match the function argument and return value. You might "get away with it" apart from that you are comparing `c` with `EOF`. — Weather Vane, Apr 21 '15 at 14:50

Can't get fwrite to work properly

2 Answers2