strstr() Runtime Error - HELP!

[arshad115]

i have made this strstr() function,it gives the correct answer if it finds the correct string inside the another but the program crashes if it does not find the string,gives a runtime error,compliler does not give any error!

here is my code:

char *astrstr(const char *s1,const  char *s2)
{
	char *p=NULL;

	int x=astrlen(s1);
	int y=astrlen(s2);

	int o=0,z=0;
	for(int i=0;i<x; i++)
	{
		for(int k=0;k<y;k++)
		{
			if(s1[i]==s2[k])
				{	o=0;z=0;	
						for(int l=i;l<x;l++)
						{
							if(s1[o+i]==s2[o])
							{
								z++;
							}
							o++;
						}
			
			
				}
				
				if(z==y)
					{
						return (char *)(s1+i);
				
					}
		}
	}
return p;
	
}

int _tmain(int argc, _TCHAR* argv[])
{
	char s[]={"this is a simple string"};
	char t[]={"is"};
	cout << " S: "<< s << endl << " T: "<< t << endl << endl;
	
	cout  << "My Function: " << endl <<  astrstr(s,t) << endl << " String Function : " << endl << strstr(s,t) << endl  << "S: "<< s << endl << "T: "<< t << endl;
	
	
	
	return 0;
}

[vivekc++]

What's the error you are getting.

[arshad115]

Error(msg BOX):
Assignment 3_Question 2.exe has encountered a problem and needs to close. We are sorry for the inconvenience.

[vivekc++]

When you doesn't find the string function astrstr returns a null pointer which is not a bad thing;
So, you need to this -

char *ptr = astrstr;
if(ptr)
cout<<*ptr;

[arshad115]

When you doesn't find the string function astrstr returns a null pointer which is not a bad thing;
So, you need to this -

char *ptr = astrstr;
if(ptr)
cout<<*ptr;

your code is totally wrong,it will never work!

[vivekc++]

Yes it seems I was in a hurry but I hope you understand the point.

Instead of simply
cout<<astrstr((s,t);

collect the pointer and then check whether it is null or not.

char *ptr=astrstr(s,t);
if(ptr)
cout<<ptr;

Because your function astrstr is returning null pointer i.e. for string
"this is a simple string\0"
pointer which you are returning in case of failure is pointing to last charachter which is '\0' .

[mvmalderen]

Hmm, this makes me thinking about an override somewhere in your program ...

What happens if you change:

int x=astrlen(s1);
int y=astrlen(s2);

To:

int x=astrlen(s1)-1;
int y=astrlen(s2)-1;

????

[arshad115]

it gives the same error!...
btw i checked the string.h function and it also gave a runtime error for the same values......thats weird!

[mvmalderen]

With me your program just compiles and works perfectly, you're maybe using another compiler ...
You've luck you aren't running Win9x, otherwise you risk a system crash instead of a program crash ;) ...

[arshad115]

lol...i m using Visual Studio express edition 2008

[mvmalderen]

Maybe you should try compiling with MinGW instead, your code is 100% working !!!

[arshad115]

Maybe you should try compiling with MinGW instead, your code is 100% working !!!

i havent used it,but i will give it a try!

[mvmalderen]

BUG REPORT!
Seems like your program doesn't want the following string: char str1[] = "test hello aatttttttttttttttttttttttttttttttttttttttttttttttt"; Here's the code:

#include <iostream>

using namespace std;

char *astrstr(const char *s1, const  char *s2)
{
    char *p = NULL;

    int x = astrlen(s1);
    int y = astrlen(s2);

    int o = 0, z = 0;
    for(int i = 0; i < x; i++)
    {
        for (int k = 0; k < y; k++)
        {
            if (s1[i] == s2[k])
            {
                o = 0;
                z = 0;
                for(int l = i; l < x; l++)
                {
                    if(s1[o+i] == s2[o])
                    {
                        z++;
                    }
                    o++;
                }


            }

            if (z == y)
            {
                return (char *)(s1+i);

            }
        }
    }
    return p;
}

int main(void)
{
    char str1[] = "test hello aatttttttttttttttttttttttttttttttttttttttttttttttt";
    char str2[] = "hello";

    cout << "C++ function: " << strstr(str1, str2) << endl;
    cout << "My function: " << astrstr(str1, str2) << endl;

    return 0;
}

The standard C++-function gives the right output, however your function's output is nothing ...

[mvmalderen]

The error is probably located where the function returns its value
(line 35 in the code I posted in the previous message) ...

[arshad115]

BUG REPORT!
Seems like your program doesn't want the following string:
char str1[] = "test hello aatttttttttttttttttttttttttttttttttttttttttttttttt";
The standard C++-function gives the right output, however your function's output is nothing ...

my poor function couldn't handle an array of 61 characters!...

i checked it,it does check conditions but somewhere it gives the array out of bound error and so gives a runtime error!

[arshad115]

The error is probably located where the function returns its value
(line 35 in the code I posted in the previous message) ...

no line 35 aint a problem,its just type casting the return type to be a pointer!
i have used it in my other functions,works well!

[ArkM]

It's a wrong algorithm (bad code started from the second for loop).
Look at working (but not optimized) code:

const char* bstrstr(const char* s, const char* p)
{
    if (s == 0 || p == 0)   // guard
        return 0;
    int slen = strlen(s);   // (astrlen;)
    int plen = strlen(p);   //   -*-*-

    if (plen == 0)  // booster
        return s + slen;
    int k, n = slen - plen + 1;
    for (int i = 0; i < n; ++i, ++s) {
        if (*s == p[0]) {
            for (k = 1; k < plen && s[k] == p[k]; ++k)
                ;
            if (k == plen)
                return s; 
        }
    }
    return 0;
}
inline
char* bstrstr(char* s, const char* p) {
    return const_cast<char*>(bstrstr(
        const_cast<const char*>(s),p));
}