CODEWITHSUNDEEP
c
user5767271
user5767271

Reputation:

Segmentation fault, basic File Input/Output

I'm copying a source file source.txt to another file destination.txt. Both of these .txt file exist in directory before running the code & each file contain only a single sentence. But I'm seeing error: Segmentation fault in terminal output. Here is the C code:

#include<stdio.h>
#include<stdlib.h>
int main(void) {
FILE* sptr = NULL;
FILE* dptr = NULL;
int ch = 0;
if((sptr = fopen("source.txt", "r")) == NULL) {
    printf("Error in opening source file.\n");
    exit(1);
}
if((sptr = fopen("destination.txt", "w")) == NULL) {
    printf("Error in opening destination file.\n");
    exit(1);
}
while((ch = fgetc(sptr)) != EOF) 
    fputc(ch, dptr);
fclose(sptr);
fclose(dptr);
return 0;
}

Upvotes: 0

Views: 534

Answers (3)

user3629249
user3629249

Reputation: 16550

the following code:

  1. properly sets the FILE* variables
  2. properly checks and displays error messages
  3. properly uses the EXIT_FAILURE macro from stdlib.h

and now, the code

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

int main(void)
{
    FILE* sptr = NULL;
    FILE* dptr = NULL;
    int ch = 0;

    if((sptr = fopen("source.txt", "r")) == NULL)
    {
        perror("fopen to read source.txt failed");
        exit( EXIT_FAILURE );
    }

    if((dptr = fopen("destination.txt", "w")) == NULL)
    {
        perror("fopen to trucante/write destination.txt failed");
        exit( EXIT_FAILURE);
    }

    while((ch = fgetc(sptr)) != EOF)
        fputc(ch, dptr);

    fclose(sptr);
    fclose(dptr);
    return 0;
}

initial conditions:

source.txt contains: 

this is a sentence

destination.txt contains: 

this will be overwritten

after running the program:

source.txt contains: 

this is a sentence

destination.txt contains: 

this is a sentence

Upvotes: 0

Kamal Palei
Kamal Palei

Reputation: 2022

You are writing to destination file like

fputc(ch, dptr);

Please note that dptr is null when above line is executed.

Hence segmentation fault.

Upvotes: 2

user7881131
user7881131

Reputation:

Looks like you've fallen for copy-and-paste-itis!

if((sptr = fopen("source.txt", "r")) == NULL) {
    printf("Error in opening source file.\n");
    exit(1);
}
if((sptr = fopen("destination.txt", "w")) == NULL) {
    printf("Error in opening destination file.\n");
    exit(1);
}

sptr is repeated, so the file is only open for writing. Trying to read from it could cause the segmentation fault.

Also, why do you complicate your variable initialising? This could just be written as:

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

int main(void) {
    FILE* sptr = fopen("source.txt", "r");
    FILE* dptr = fopen("destination.txt", "w");
    int ch = 0;

    if(sptr == NULL) {
        printf("Error in opening source file.\n");
        exit(1);
    }

    if(dptr == NULL) {
        printf("Error in opening destination file.\n");
        exit(1);
    }

    while((ch = fgetc(sptr)) != EOF) 
        fputc(ch, dptr);

    fclose(sptr);
    fclose(dptr);
    return 0;
}

Upvotes: 2

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