CODEWITHSUNDEEP
cstring
Sukrit Kapil
Sukrit Kapil

Reputation: 103

Why am I getting segmentation fault for the following code?

The question is to alphabetically sort the given string inputs in ascending order. I wrote the following code for the same. But after printing the entered names the program instead of sorting the strings is giving segmentation fault. I have spent good time over the issue but couldn't figure out anything. Any help would be appreciated.

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main()
{
    int x,i,j,length;
    printf("Enter the number of names you want to sort.\n");
    scanf("%d",&x);
    char *names[x],*p,name[50],*t;
    printf("Enter the names:\n");
    for(i=0;i<x;i++)
    {
        scanf(" %[^\n]",name);
        length = strlen(name);
        p = (char *)malloc(length+1);
        strcpy(p,name);
        names[i] = p;
    }
    printf("Entered names are:\n\n");
    for(i=0;i<x;i++)
    {
        printf("%s\n",names[i]);
    }
    printf("\n\nThe sorted names are:\n");
    for(i=0;i<x-1;i++)
    {

        for(j=i+1;j<x;j++)
        {
            if(strcmp(names[i],names[j])>0)
            {
                strcpy(t,names[i]);
                strcpy(names[i],names[j]);
                strcpy(names[j],t);
            }
        }    
    }
    for(i=0;i<x;i++)
    {
        printf("%s\n",names[i]);
    }
    return 0;
}

Upvotes: 2

Views: 94

Answers (1)

Matthieu
Matthieu

Reputation: 3117

You didn't allocate t so the strcpy(t,names[i]) will segfault.

You can also use strdup()1 to duplicate your strings (instead of malloc() and strcpy()).

And, as your array is of char* elements, you can just swap them directly:

t=names[i];
names[i]=names[j];
names[j]=t;

Regarding your question about pointers, you can consider pointers as uint32_t: they are ”just" values you can assign, like regular integers. It's just their value that is interpreted as an address, rather than a random integer (i.e. its value has a special meaning for the computer, as it is strongly linked to memory).

1: As noted by @WhozCraig, strdup() is not part of the standard library so you'll have to #include the appropriate headers for your platform (it is really widely spread though and hardly a problem).

Upvotes: 6

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