Why does the following code for bubble sort give segmentation fault?

Question

#include<stdio.h>
#include<string.h>
int main(){
    char *a[]={"this","is","a","string"};
    char temp[100];
    for(int i=0;i<3;i++){                               
        for(int j=0;j<3-i;j++){
            if(strcmp(a[j],a[j+1])>0){
                strcpy(temp,a[j]);
                strcpy(a[j],a[j+1]);
                strcpy(a[j+1],temp);
            }
        }
    }
    for(int i=0;i<4;i++){
        printf("%s\n",a[i]);
    }
}

The following code is for bubble sorting the strings.It gives segmentation fault.What is wrong in it?

score 3 · Answer 1 · answered Feb 20 '18 at 12:53

3

String literals are read-only in C. Your strcpy(a[j],a[j+1]) and strcpy(a[j+1], temp) calls are illegal.

answered Feb 20 '18 at 12:53

Navneeth

373
3
15

Thanks a lot.But the code [here](https://www.geeksforgeeks.org/sorting-strings-using-bubble-sort-2/) does the same thing and runs well – Vedant Feb 20 '18 at 13:04
1

Note that that algorithm operates on `char arr[][MAX]` and not on `char*[MAX]` – Davide Spataro Feb 20 '18 at 13:06
1

@Vedant That code sorts array of character *arrays*. You are sorting array of *pointers*. – user694733 Feb 20 '18 at 13:06
okay thanks @DavideSpataro – Vedant Feb 20 '18 at 13:11

Davide Spataro · Answer 2 · 2018-02-20T15:43:20.210

3

There is no need to use strcpy. The only thing that you have to do is to swap a[j] and a[j+1] pointers.

Make sure that the for loop have the correct bounds. The array has size 4, and valid elements are in the range [0..4)

Take a look at the following:

int main(){
        char const *a[]={"this","is","a","string"}; //const added
        char *temp = 0; // a simple pointer
        for(int i=0;i<4;i++){     //bounds changed                          
                for(int j=0;j<4-1;j++){
                        if(strcmp(a[j],a[j+1])>0){ // swap pointers
                            temp = a[j];
                            a[j] = a[j+1];
                            a[j+1]=temp;
                        }
                }
        }
        for(int i=0;i<4;i++){
                printf("%s\n",a[i]);
        }
}

edited Feb 20 '18 at 15:43

answered Feb 20 '18 at 12:59

Davide Spataro

7,319
1
24
36

Why is using strcpy() not allowed? – Vedant Feb 20 '18 at 13:06
Take a look at the following. https://stackoverflow.com/questions/164194/why-do-i-get-a-segmentation-fault-when-writing-to-a-string-initialized-with-cha . Please be aware that avoiding `strcpy` altogether translates to a much more efficient function. – Davide Spataro Feb 20 '18 at 13:08
Im sorry, that was meant to be 3-i and not 3-1. – Vedant Feb 20 '18 at 13:12

Why does the following code for bubble sort give segmentation fault?

2 Answers2