read and write from and into file

Question

I'm trying to write a function which get numbers from the user and, put them in file and then reads them and find the minimun. this is the code I wrote but It doesn't work at all. can someone please help me understand what I'm doing wrong? I'm new to C.

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

int min_call(int, ...);


int main()
{
    int min;
    min = min_call(90,78,5,20,-1);
    printf("\n the minimum number is: %d ", min);

    min = min_call(70,40,2,-1);
    printf("\n the minimum number is: %d ", min);

    min = min_call(40,30,-1);
    printf("\n the minimum number is: %d ", min);

    return 0;
}


int min_call(int first, ...)
{
    int min;
    int currentNum;
    int i;
    va_list args;
    va_start(args,first);

    FILE *fd;

    if(!(fd=fopen("min_call_file.txt","a")))
    {
        fprintf(stderr, "cannot open file \n");
        exit (0);
    }

    for(i = first; i>=0; i=va_arg(args, int))
    {
        fprintf(fd, "%d", i);
    }
    va_end(args);

    fseek(fd,0,SEEK_SET);
    min = fgetc(fd);
    do
    {
        currentNum = fgetc(fd);
        if(currentNum < min)
            min = currentNum;


    }while(!feof(fd));

    fclose(fd);
    return min;
}

Your use of `while (!feof())` is [wrong](http://stackoverflow.com/q/5431941/3185968) — EOF, Jan 17 '17 at 18:23
@EOF you have the most appropriate username in SO to post that comment. — CPHPython, Jan 17 '17 at 18:27
@CPHPython It's noticeable whenever I need to tell somebody not to store the return value of `getchar()` to a `char`-type variable... — EOF, Jan 17 '17 at 18:29
`fgetc(fd)` returns value in the `unsigned char` range and `EOF`, a negative number. `min` will always end up as `EOF`. Exit the loop (or don't enter it) when `fgetc()` returns `EOF`. Perhaps other issues too. — chux - Reinstate Monica, Jan 17 '17 at 18:31
yes, the file consist the first input only. the main didn't print to the screen nothing, and the program didn't exit. — Ofir Sasson, Jan 17 '17 at 18:38
Can't you just keep track of how many numbers you read from input, and use that instead of testing for EOF? — bruceg, Jan 17 '17 at 18:46
You can't read from a file stream that's opened in `"a"` mode! You'd need either `"r"` mode or a `"+"` in the mode to be able to read from the file. — Jonathan Leffler, Jan 17 '17 at 19:23

BLUEPIXY · Answer 1 · 2017-01-17T19:42:33.013

fix like this

int min_call(int first, ...){
    int min;
    int currentNum;
    int i;
    va_list args;
    va_start(args,first);

    FILE *fd;

    if(!(fd=fopen("min_call_file.txt","w+"))){//w : new write each call, a : Straddle the call, + : To read later
        fprintf(stderr, "cannot open file \n");
        exit (0);
    }

    for(i = first; i>=0; i=va_arg(args, int)){
        fprintf(fd, "%d ", i);//put space after %d because Delimiter is required
    }
    va_end(args);

    fflush(fd);//Flush the buffer and to establish  the write
    fseek(fd, 0, SEEK_SET);
    fscanf(fd, "%d", &min);//read integer, not character
    do {
        if(1==fscanf(fd, "%d", &currentNum) && currentNum < min){
            min = currentNum;
        }
    }while(!feof(fd));

    fclose(fd);
    return min;
}

read and write from and into file

1 Answers1