Is the File pointer causing segmentation fault in code

Question

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdarg.h>
#include <sys/types.h>
#include <stdlib.h>
#include <signal.h>
#include <sys/wait.h>

char date[35] = {"0"};

void main()
{
        FILE *fp;
        char ch;
        int i=0;

        if(fork() == 0)
        {
                system("date '+%Y-%m-%d %H:%M:%S' > date.txt");
                exit(0);
        }
        wait(0);

        fp = fopen("date.txt","w+");
        if(fp == 0) {return;}

        while((ch = fgetc(fp)) != EOF)
        {
                date[i++] = (char)ch;
        }
        fclose(fp);
        date[i] = '\0';

        printf("date = %s", date);
}

I keep on getting segmentation fault in this code. I have even tried creating the file named "date.txt" manually.

The command date '+%Y-%m-%d %H:%M:%S' > date.txt works on bash separately well.

Can someone please help me find, what am I doing wrong?

[update:] Forgot to initialize i = 0. Edited but still the segment violation persists.

Here `date[i++]` what is `i` value ? you didn't initialize `i`. — Achal, Jun 15 '18 at 08:19
Thanks. I have now initiliazed `i =0` . Still I get the segment violation @ — Doherty, Jun 15 '18 at 08:22
Also if you open file in `w+` mode, what this `fgetc(fp))` will store into `date` ? Nothing. Bcz `w+` means first it will truncate old data and then write/read. — Achal, Jun 15 '18 at 08:22
If changing char to int solved your problem, you can mark the answer as correct by clicking the check mark under the voting buttons. (This will also give you two reputation points) — hat, Jun 15 '18 at 13:35

score 1 · Answer 1 · answered Jun 15 '18 at 08:29

1

You are using a char value to check against EOF, but since EOF is a numeric value, ch will never be equal to EOF. This means that your loop will run forever, overrunning your array, which only has 35 elements. You have to use int ch instead.

answered Jun 15 '18 at 08:29

hat

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score 0 · Answer 2 · answered Jun 15 '18 at 08:23

0

You should to initial variable i or it gets a random value.

void main()
{
    FILE *fp;
    char ch;
    int i = 0;
...
}

answered Jun 15 '18 at 08:23

Dennis Vash

50,196
9
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Thanks. Stupid mistake. I initialized i = 0. However, the segment violation is still persisting – Doherty Jun 15 '18 at 08:25
I dont get any segfault, try to provide example of desired output – Dennis Vash Jun 15 '18 at 08:28

score 0 · Answer 3 · answered Jun 15 '18 at 08:28

0

The statement overflowed the max size of 35. That means i become greater than 0..34.

date[i++] = (char)ch;

answered Jun 15 '18 at 08:28

I. Ahmed

2,438
1
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Is the File pointer causing segmentation fault in code

3 Answers3