CODEWITHSUNDEEP
c
karan2996
karan2996

Reputation: 11

I'm getting Runtime Error : Segmentation Fault (SIGSEGV), why?

I am getting a runtime error in this and i can't seem to figure it out. This is my code to reverse a string and change A to T and vice-versa and to change C to G and vice-versa,

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

char* reverse(char *input)
{
    int len=strlen(input);
    char *rev=NULL;
    rev=(char*)malloc(sizeof(char)*len);
    int i,k=0;
    for(i=len-1;i>=0;i--)
    {
        rev[k++]=input[i];
        if(rev[k-1]=='A')
            rev[k-1]='T';
        else if(rev[k-1]=='T')
            rev[k-1]='A';
        else if(rev[k-1]=='C')
            rev[k-1]='G';
        else if(rev[k-1]=='G')
            rev[k-1]='C';
    }
    rev[k]='\0';
    return rev;
}

int main()
{
    char *input=(char *)malloc(sizeof(char)*1000);
    scanf("%s",input);
    char *str =NULL;//(char*)malloc(sizeof(char)*1000);
    str=reverse(input);
    printf("%s",input);
     free(input);
}

Upvotes: 1

Views: 85

Answers (2)

Gerhardh
Gerhardh

Reputation: 12404

You do not allocate enough memory to hold your reversed string:

int len=strlen(input);
...
rev=(char*)malloc(sizeof(char)*len);
...
rev[k]='\0';

You missed 1 extra byte for the terminating \0.

And by the way... Please don't cast the return value from malloc to a pointer.

Upvotes: 4

kkica
kkica

Reputation: 4104

First of all, you use i++ instead of i-- in the for loop. That means that the for loop never ends and k gets very very big and your rev[k] atempts to access values that it shouldnt.

Secondly, you do not need to allocate memory for str, because you allocate it in the function.

And you should allocate memory for one more char in the function as you will need if for '\0'.

Upvotes: 1

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