How to read from binary file to a text file in C?

Question

I am having trouble copying from a binary file and writing to a text file. I have written a program that is capable of copying from a text file and writing to a binary file but I cannot do the reverse.

Here is my function that I am having issues with:

void CopyBin2Text(char* rafname, char* txtname)
{

FILE * fraf = fopen(rafname,"rb");
FILE * ftxt = fopen(txtname,"r+");

//READ FROM BINARY FILE
struct PERSON p;
int ByteOfBin;


printf("ID \t NAME \t\t BALANCE \n");
printf("---------------------------------------\n");

when I run my program it stops here after printing the above statement

  while(!feof(fraf))
  {
       fscanf(fraf, "%d %s %f", &p.ID, p.name, &p.balance);

    ByteOfBin = ((p.ID/10-1)*sizeof(p));
    fseek(ftxt,ByteOfBin, SEEK_SET);
    fwrite((char *)&p, sizeof(p), 1, ftxt);

  }


fclose(fraf);
fclose(ftxt);
}

Another issue that I have noticed is that the text file becomes to large to open. The result is that I have to delete the text file and create it again. Can anyone explain what is causing this to occur?

You say that the file you read is binary, but then you attempt to read from it like a text file? *And* you write to the text file like a binary file? — Some programmer dude, Oct 21 '15 at 06:16
Functions like `fscanf()` were not designed to work with binary files. They expect text, that should be provided in a specific standard supported by the language. — Havenard, Oct 21 '15 at 06:16
Take a look at [**Why is “while ( !feof (file) )” always wrong?**](http://stackoverflow.com/questions/5431941/why-is-while-feof-file-always-wrong?s=1|2.6488) You need to check the return of `fscanf` (and you should probably be reading `char-by-char` from the binary file or using `fread` instead of `fscanf` -- which is for formatted text...) — David C. Rankin, Oct 21 '15 at 06:16
I have replaced `fscanf` with the following statement: `fread((char *)&p, sizeof(p),1,fraf);` and the content from the binary file is showing in the text file however it is in binary format and not text format. — JonSnow, Oct 21 '15 at 07:32
If you want the output file in text format you must write each of the fields of `p` to it with a text-writing function such as `fprintf(ftxt,"%d\t",p.ID)` — Weather Vane, Oct 21 '15 at 07:49

score 5 · Accepted Answer · answered Oct 21 '15 at 08:20

I made a number of changes to your function. The file opening mode, checking they did open, dumping the feof(), using the appropriate binary and text functions to read and write, and returning a status for whether the function operated properly.

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

struct PERSON {
    int ID;
    char name[20];
    float balance;
};

int CopyBin2Text(char* rafname, char* txtname)      // changed return value
{
    FILE *fraf, *ftxt;
    struct PERSON p;
    if ((fraf = fopen(rafname,"rb")) == NULL)
        return 0;                                   // failure

    if ((ftxt = fopen(txtname,"wt")) == NULL) {     // changed mode
        fclose(fraf);
        return 0;                                   // failure
    }
    fprintf(ftxt, "ID\tNAME\tBALANCE\n");
    fprintf(ftxt, "---------------------------------------\n");
    while(fread(&p, sizeof(p), 1, fraf) == 1)       // use return value to loop
        fprintf(ftxt, "%d\t%s\t%.2f\n", p.ID, p.name, p.balance);
    fclose(ftxt);

    fclose(fraf);
    return 1;                                       // success
}

int makefile(char* rafname)
{
    FILE *fraf, *ftxt;
    struct PERSON p = {1,"alpha", 123.45};
    struct PERSON q = {2,"beta",  100.00};
    struct PERSON r = {3,"gamma", 9.99};
    if ((fraf = fopen(rafname,"wb")) == NULL)
        return 0;                                   // failure
    fwrite(&p, sizeof(p), 1, fraf);
    fwrite(&q, sizeof(q), 1, fraf);
    fwrite(&r, sizeof(r), 1, fraf);
    fclose(fraf);
    return 1;                                       // success
}

int main(void)
{
    if (makefile("file.bin") == 0)
        printf("Failure\n");
    else {
        if (CopyBin2Text("file.bin", "file.txt") == 0)
            printf("Failure\n");
        else
            printf("Success\n");
    }
    return 0;
}

Output text file is

ID  NAME    BALANCE
---------------------------------------
1   alpha   123.45
2   beta    100.00
3   gamma   9.99

How to read from binary file to a text file in C?

1 Answers1