how to print all character from file with its position in c?

Question

hello i wrote below a program in c,

#include <stdio.h>
#include <conio.h>

void main()
{
    FILE *fp;
    char c;
    long n=0L;
    fp=fopen("myfile.txt","w");
    printf("Enter the data into file:\n");
    while((c=getchar())!=EOF)
    {
        putc(c,fp);
    }
    printf("Total character into file:%ld\n",ftell(fp));
    fclose(fp);
    fp=fopen("myfile.txt","r");
    while(feof(fp)==0)
    {
        fseek(fp,n,0);
        printf("\n char:'%c' at position '%ld'",getc(fp),ftell(fp));
        n++;
    }
    fclose(fp);
    getch();
}

it work fine but when i replace the statement:

printf("\n char:'%c' at position '%ld'",getc(fp),ftell(fp));

with the statement:

printf("\n position '%ld'",ftell(fp));

then it will going to infinite loop
I knew the function,

fseek()

It set the file pointer to specified position. but here what happen,i don't understand. please help me.

It has nothing to do with the compiler, it's specified by the standard, if borland c compiler which I don't know is not compliant with that use another compiler, `gcc` and `clang` are great. — Iharob Al Asimi, Feb 14 '15 at 14:07
And [`while(feof(fp)==0)` is always wrong](http://stackoverflow.com/questions/5431941/while-feof-file-is-always-wrong) — Iharob Al Asimi, Feb 14 '15 at 14:08
the feof(fp) will return the 0 if file file end no encountred. otherwise it will return the non-zero value. — Harish, Feb 14 '15 at 14:10
Also, please use macros instead of their values, they are macros for a reason `fseek(fp, n, 0);` -> `fseek(fp, n, SEEK_SET);`. — Iharob Al Asimi, Feb 14 '15 at 14:11
no i get the different position continuously and my program is going to infinite loop — Harish, Feb 14 '15 at 14:12
Yes it is `0` but it's a macro because if someone ever decided to change it, it will not break your code. — Iharob Al Asimi, Feb 14 '15 at 14:21
Why are you trying to `fseek()` `fgetc()` will get one character at a time, and `ftell()` will give you current position in the stream, seeking has a different purpose, can you explain why are you trying that? — Iharob Al Asimi, Feb 14 '15 at 14:22
i tried to make program, which give me character with its position from file. — Harish, Feb 14 '15 at 14:26
hello BLUEPIX , the `feof() ` will automatically encountered the end of file by `EOF` — Harish, Feb 14 '15 at 14:28
`fseek` clears the terminal state of the file. So `feof()` will not be true. — BLUEPIXY, Feb 14 '15 at 14:30

Kavindu Dodanduwa · Accepted Answer · 2015-02-14T14:36:29.187

Reason for infinite loop : In your second case you do not progress the stream as in first case

getc()

Returns the character currently pointed by the internal file position indicator of the specified stream. The internal file position indicator is then advanced to the next character.

A solution :

#include <stdio.h>

void main()
{
    FILE *fp;
    char c;

    long n = 0L;
    fp=fopen("main.c","r");

    while(getc(fp)!=EOF)
    {
        fseek(fp,n,0);
        printf("\n position '%ld'",ftell(fp));
        n++ ;
    }
    fclose(fp);

}

Furthermore :

fseek() do not progress the file pointer.

Sets the position indicator associated with the stream to a new position.

feof()

This indicator is generally set by a previous operation on the stream that attempted to read at or past the end-of-file."

So this explains your failure. Second implementation does not come across EOF as first case. Provided sample of code would provide you an workaround.

score 0 · Answer 2 · answered Feb 14 '15 at 14:24

Check in documentation if fseek or ftell sets feof() result. Possibly not, so when you removed getc call feof can no longer return 'true', hence infinite loop.

Anyway, are you interested in the explanation why this program behaves strange or rather how you should write your program properly to achieve the result described...?

score 0 · Answer 3 · answered Feb 14 '15 at 14:28

fseek() will not set the EOF marker, and in fact it can unset the EOF marker and it should do it after a succesful call.

Also, as the link points out the while (feof(fp) == 0) is always wrong, it's because you need to fgetc() one extra char for the EOF marker to be set, so you will have one extra iteration, instead you have to do it this way

#include <stdio.h>

int main()
{
    FILE    *fp;
    int      c; /* this should be 'int' and not 'char' */
    long int n;

    fp = fopen("myfile.txt", "w");
    if (fp == NULL)
        return -1;
    printf("Enter the data into file:\n");
    while ((c = getchar()) != EOF)
        putc(c, fp);
    printf("Total character into file:%ld\n", ftell(fp));
    fclose(fp);

    fp = fopen("myfile.txt","r");
    if (fp == NULL)
        return -1;
    while ((c = fgetc(fp)) != EOF)
    {
        if (c == '\n')
            printf("charcater `\\n' at position '%ld'\n", ftell(fp));
        else
            printf("charcater `%c' at position '%ld'\n", c, ftell(fp));
        n++;
    }
    fclose(fp);

    return 0;
}

score 0 · Answer 4 · answered Feb 14 '15 at 14:28

0

A successful call fseek function clear the end-of-file indicator, but your loop condition rely on feof, so feof(fp) == 0 always true.

answered Feb 14 '15 at 14:28

alijandro

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jschultz410 · Answer 5 · 2015-02-14T14:36:19.070

fseek(SEEK_SET) merely sets the FILE's pointer to a position in the file. It doesn't actually do any reading of the file or anything. So, it will gladly let you set the position to WAY past the end of the file (and it clears any existing EOF set on the stream). ftell() merely returns the position of the file pointer.

Without doing a read of some sort (e.g. - getc()), EOF won't be set on the stream and your loop will be infinite.

You can do a fseek(fp, 0, SEEK_END) and then an ftell() to know the size / end of the file position.

PS - You really need to check your return values more carefully and handle any failures.

how to print all character from file with its position in c?

5 Answers5