Thread: Sig fault

Code:

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

const char* search1="";
const char* search2="apple";
const char* search3="apple tree";

char* strings1[3]={"","",""};
char* strings2[3]={"app","apple treehouse","apple treehouse"};

char* match(const char* search, char** strings, int n) {
   if (n==0) {
      return "";
   }
   if (n==1) {
      if (!strcmp(search, "")) {
         return strings[0];
      }
      else {
         if (!strncmp(strings[0], search, strlen(search))) {
            return strings[0];
         }
         else return "";
      }
   }
   
  
   if (n>1) {
      int i=1;
      int j=n-1;
      int k=1;
      char result[20]="";
      if (!strcmp(search, "")) {
         while (j--) {
            if (!strncmp(strings[0], strings[i++], k)) continue;
            else return "";
         }
         strncpy(result, strings[0], 1);
         result[1]='\0';
         char* r=(char*)malloc(20*sizeof(char));
         strcpy(r, result);
         k++;
         i=1;
         j=n-1;
         while (k++<=strlen(strings[0])) {
            while (j--) {
               if (!strncmp(strings[0], strings[i++], k)) continue;
               else return r;
           }
           strncpy(result, strings[0], k);
           result[k]='\0';
           strcpy(r, result);
           puts(r);
         }
         strcpy(r, strings[0]);
         return r;
      }
   }
}

int main() {
   match(search1, strings2, 3);
   return 0;
}

This gives seg fault. Why? Thanks.

For starters, line 48 (the strncmp) inevitably will access the array out of bounds..

Also, if you are making anything larger out of this, you need to get rid of the globals.

Originally Posted by memcpy

For starters, line 48 (the strncmp) inevitably will access the array out of bounds..

Also, if you are making anything larger out of this, you need to get rid of the globals.

Thanks. I had to reset i and j to their original values inside while loop. Here's code returning "app" as expected after matching.

Code:

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

const char* search1="";
const char* search2="apple";
const char* search3="apple tree";

char* strings1[3]={"","",""};
char* strings2[3]={"app","apple treehouse","apple treehouse"};

char* match(const char* search, char** strings, int n) {
   if (n==0) {
      return "";
   }
   if (n==1) {
      if (!strcmp(search, "")) {
         return strings[0];
      }
      else {
         if (!strncmp(strings[0], search, strlen(search))) {
            return strings[0];
         }
         else return "";
      }
   }
   
  
   if (n>1) {
      int i=1;
      int j=n-1;
      int k=1;
      char result[20]="";
      if (!strcmp(search, "")) {
         while (j--) {
            if (!strncmp(strings[0], strings[i++], k)) continue;
            else return "";
         }
         strncpy(result, strings[0], 1);
         result[1]='\0';
         char* r=(char*)malloc(20*sizeof(char));
         strcpy(r, result);
         k++;
         i=1;
         j=n-1;
         while (k++<=strlen(strings[0])) {
            while (j--) {
               if (!strncmp(strings[0], strings[i++], k)) continue;
               else return r;
           }
           i=1; j=n-1;
           strncpy(result, strings[0], k);
           strcpy(r, result);
         }
         return r;
      }
   }
}

int main() {
   puts(match(search1, strings2, 3));
   return 0;
}