segmentation fault


 
Thread Tools Search this Thread
Top Forums Programming segmentation fault
# 1  
Old 07-06-2010
segmentation fault

Hi,

I am having this segmentation fault not in the following program, bt. in my lab program . My lab program is horrible long so cannot post it here bt. I am using the following logic in my program which is giving the segmentation fault. Bt. if I run this sample program as it is it dosen't give the error. It is freaking me out Smilie
Code:
#include<stdio.h>
#include<string.h>
#include<stdlib.h>

void *fxn();
 
typedef struct coord{
    int x;
//    int y;
    }cord ;

int main()
{
void *pt;
cord a, *p;
int x2, y2;

pt =fxn();
p = &a;
p = pt;

printf(" %d ",p->x);
}

void *fxn()
{
cord b,*point;
point = &b;

int x1= 10, y1= 10;

point->x = x1;
// point->y = y1;
return(point);
}

thanks a tonn in advance.
# 2  
Old 07-06-2010
I think that the main issue with that code is that fxn() returns a pointer to a variable that is local to fxn() itself, which is deallocated when the function returns.
There are other minor problems of course, and I guess this code is only aimed at practicing with C pointers, but your segmentation fault should disappear if you trying solving that problem.

bye
# 3  
Old 07-06-2010
Yes, local variables like that and pointers to them don't remain valid after the function call they exist inside returns. That it works at all is simply a coincidence. Make a few more function calls and the memory pointed to will probably be overwritten with garbage.

The compiler is probably warning you about this mistake, but as a warning, not an error.

You should pass a pointer to that function instead of getting one from it. Don't let it give you its local variables, give yours to it; perfectly valid when done before your function returns.
Code:
void fn(int *val)
{
       (*val)=3;
}

int main(void)
{
        int n;

        fn(&n);

        printf("n=%d\n", n);

        return(0);
}

You could also use a static variable, like:

Code:
int *fn(void)
{
       static int n;

        n=3;
        return(&n);
}

But this has several caveats. Static variables act like global variables; it will be pointing to the same pointer every time, so you can't keep the pointer around and expect the value to stay the same when other things use it. Also, this isn't thread-safe since multiple threads would be competing for the same variable. Probably best to pass a pointer.

Last edited by Corona688; 07-06-2010 at 07:04 PM..
This User Gave Thanks to Corona688 For This Post:
# 4  
Old 07-07-2010
Thanks a lotttt...it works wonders SmilieSmilie
Login or Register to Ask a Question

Previous Thread | Next Thread

10 More Discussions You Might Find Interesting

1. Programming

C. To segmentation fault or not to segmentation fault, that is the question.

Oddities with gcc, 2.95.3 for the AMIGA and 4.2.1 for MY current OSX 10.14.1... I am creating a basic calculator for the AMIGA ADE *NIX emulator in C as it does not have one. Below are two very condensed snippets of which I have added the results inside the each code section. IMPORTANT!... (11 Replies)
Discussion started by: wisecracker
11 Replies

2. Programming

Segmentation fault

I keep getting this fault on a lot of the codes I write, I'm not exactly sure why so I'd really appreciate it if someone could explain the idea to me. For example this code #include <stdio.h> main() { unsigned long a=0; unsigned long b=0; int z; { printf("Enter two... (2 Replies)
Discussion started by: sizzler786
2 Replies

3. Homework & Coursework Questions

Segmentation Fault

this is a network programming code to run a rock paper scissors in a client and server. I completed it and it was working without any error. After I added the findWinner function to the server code it starts giving me segmentation fault. -the segmentation fault is fixed Current problem -Also... (3 Replies)
Discussion started by: femchi
3 Replies

4. Programming

Using gdb, ignore beginning segmentation fault until reproduce environment segmentation fault

I use a binary name (ie polo) it gets some parameter , so for debugging normally i do this : i wrote script for watchdog my app (polo) and check every second if it's not running then start it , the problem is , if my app , remain in state of segmentation fault for a while (ie 15 ... (6 Replies)
Discussion started by: pooyair
6 Replies

5. UNIX for Dummies Questions & Answers

Segmentation Fault

Hi, While comparing primary key data of two tables thr bteq script I am getting this Error. This script is a shell script. *** Error: The following error was encountered on the output file. Script.sh: 3043492 Segmentation fault(coredump) Please let me know how to get through it. ... (5 Replies)
Discussion started by: monika
5 Replies

6. Programming

Why not a segmentation fault??

Hi, Why I don't receive a segmentation fault in the following sample. int main(void) { char buff; sprintf(buff,"Hello world"); printf("%s\n",buff); } If I define a buffer of 10 elements and I'm trying to put inside it twelve elements, Should I receive a sigsev... (22 Replies)
Discussion started by: lagigliaivan
22 Replies

7. AIX

Segmentation fault

Hi , During execution a backup binary i get following error "Program error 11 (Segmentation fault), saving core file in '/usr/datatools" Riyaz (2 Replies)
Discussion started by: rshaikh
2 Replies

8. Programming

segmentation fault

ive written my code in C for implementation of a simple lexical analyser using singly linked list hence am making use of dynamic allocation,but when run in linux it gives a segmentation fault is it cause of the malloc function that ive made use of????any suggestions as to what i could do??? thank... (8 Replies)
Discussion started by: rockgal
8 Replies

9. Programming

Hi! segmentation fault

I have written a program which takes a directory as command line arguments and displays all the dir and files in it. I don't know why I have a problem with the /etc directory.It displays all the directories and files untill it reaches a sub directory called peers which is in /etc/ppp/peers.the... (4 Replies)
Discussion started by: vijlak
4 Replies

10. UNIX for Dummies Questions & Answers

Segmentation Fault

hello all, I tried a program on an array to intialise array elements from the standard input device.it is an integer array of 5 elements.but after entering the 4th element it throws a message called "Segmentation Fault" and returns to the command prompt without asking for the 5th element. ... (3 Replies)
Discussion started by: compbug
3 Replies
Login or Register to Ask a Question

Featured Tech Videos