Segmentation fault when return a integer pointer or base address of the array

Question

I'm writing a program in c and I encountered an error message:

Program terminated with signal SIGSEGV, Segmentation fault.

At that time I ran that program using dev-c++ on my system then the program ran successfully until it returned:

[Warning] function returns address of local variable [enabled by default]

I am not able to understand what is happening.

Here's my program:

#include <math.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include <limits.h>
#include <stdbool.h>

int* getRecord(int s_size, int* s, int *result_size){
    int i = 0, heigh = s[0], low = s[0], heigh_count = 0, low_count = 0, a[2];
    for(i = 1; i < s_size; i++){
        if(s[i] > heigh){
            heigh_count++;
            heigh = s[i];
        }
        if(s[i] < low){
            low_count++;
            low = s[i];
        }
    }
    *result_size = 2;
    a[0] = heigh_count;
    a[1] = low_count;
    return a;
}

int main() {
    int n; 
    scanf("%d",&n);
    int *s = malloc(sizeof(int) * n);
    for(int s_i = 0; s_i < n; s_i++){
       scanf("%d",&s[s_i]);
    }
    int result_size;
    int* result = getRecord(n, s, &result_size);
    for(int i = 0; i < result_size; i++) {
        if (i) {
            printf(" ");
        }
        printf("%d", result[i]);
    }
    puts("");
    return 0;
}

Input

9

10 5 20 20 4 5 2 25 1

Output

2 4

Error log

GDB trace:
Reading symbols from solution...done.
[New LWP 17778]
Core was generated by `solution'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x000000000040065d in printf (__fmt=0x4008a7 "%d")
    at /usr/include/x86_64-linux-gnu/bits/stdio2.h:104
104   return __printf_chk (__USE_FORTIFY_LEVEL - 1, __fmt, __va_arg_pack ());
#0  0x000000000040065d in printf (__fmt=0x4008a7 "%d")
    at /usr/include/x86_64-linux-gnu/bits/stdio2.h:104
#1  main () at solution.c:41

Hmm..returning the address of an automatic local variable...what did you expect? — Sourav Ghosh, Jun 24 '17 at 14:58
i want to return integer point from the function int* getRecord(int s_size, int* s, int *result_size), we know array name is base address, that by i am returning a. — JITENDRA KUSHVAHA, Jun 24 '17 at 15:02
@JITENDRAKUSHVAHA read the linked duplicate. quick summary, `a` has automatic storage (default for variables in function scope), so it *doesn't exist any more* as soon as the function is left. — , Jun 24 '17 at 15:06
same as @FelixPalmen said, do read the lined question and answer. — Sourav Ghosh, Jun 24 '17 at 15:07

score 1 · Accepted Answer · answered Jun 24 '17 at 15:08

1

The warning

function returns address of local variable

pretty much says it all. You can't return array a as an int*.

a is destroyed when getRecord() returns so you are left with result holding a pointer to invalid data, and you will get a segmentation fault when trying to access result[i].

If you put a on the heap with malloc, you will probably be fine, but there is still a weird mixture of pointers and arrays here.

answered Jun 24 '17 at 15:08

Mark Ch

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thank you so much Mark Ch for clearing my doubt..... – JITENDRA KUSHVAHA Jun 24 '17 at 18:41

Segmentation fault when return a integer pointer or base address of the array

1 Answers1