Writing my own strstr function that finds multiple matches
Jul 25, 2013 at 7:18pm UTC
Hello. I am trying to write my own version of the strstr() function that can find multiple matches. The function should return the number of matches found, and retStrings should contain a contiguous list of char* pointers that point to the first character of each match. Apparently, my understanding of pointers is lacking somewhere...
Here's what my StrStr function looks like right now:
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unsigned int StrStr(const char * str, const char * target, char ** retStrings){
int strlength = 0, targetlength = 0, i = 0, counter = 0;
char * tempptr = '\0' ;
strlength = strlen(str);
targetlength = strlen(target);
cout<<strlength<<endl<<targetlength<<endl;
for (i = 0; i < strlength; i++){
if (strncmp(str+i,target,targetlength)==0){ //a match was found
tempptr = (char *)str+i;
retStrings[counter] = tempptr;
counter++;
}
}
return counter;
}
int main()
{
const char teststring[] = "This is a test string of test words and other tests\0" ;
const char testtarget[] = "test\0" ;
char ** stringtable;
int i;
cout<<"Attempting custom StrStr..." <<endl;
cout<<StrStr(teststring,testtarget,stringtable);
cout<<"Attempting built-in strstr..." <<endl;
cout<<strstr(teststring,testtarget);
cin >> i;
return 0;
}
As it is now, it crashes in the if statement. Can any fresher eyes see what I'm doing wrong?
Jul 25, 2013 at 7:50pm UTC
stringtable points to some random place in memory. You treat it as though it does not.
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const unsigned reasonablyLargeValue = 256 ;
char * stringtable[reasonablyLargeValue] ;
Jul 25, 2013 at 8:41pm UTC
Ah, I see. I tried initializing stringtable a few ways, but never exactly like that. Anyway, that did it. Thanks for your help!
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