URGENT help needed in implmenting substring for cstring!!

[ami1234]

#include<iostream>
#include<string>

using namespace std;

char* substring (char *s, int start, int end);

int main()
{
char *s="university";
char *ans;
int start, end;

ans=substring(s, 2, 5);
cout<<ans<<endl;

system("pause");
return 0;

}

char* substring (char *s, int start, int end)
{
char *ptr=NULL;
char *p=s;
for(int i=0;i<(end-start); i++)
{
*(ptr+i)=*(p+i);
}
*(++ptr)='\0';
return ptr;
}

[vince1027]

1. You did not explain what your problem is.
2. Use the code tags. They are there for a reason.

Looking at it quickly, the problem is most likely because you are trying to modify something that is put in the read-only data section of the program.

This seems to be a simple homework/assignment, so don't expect any of us to answer any more than what I said. Try to understand what my answer means first before you go follow up on this question. We like to help, but we don't want to spoon feed people.

[ami1234]

The problem is that I'm trying to get a substring from a string which has been read as a character, using the start and end values I have to extract the substring into another character pointer. I'm very new to c-string, thus some help would be valuable!!
I dnt get what ur trying to say abt the trying to modify something tht is put in the read only data section of the program!! Thank you!!

[Hassan Akram]

You are copying the substring in the function but right after that you are giving a null to 2nd index which emties your string.
moreover you need new memory for substring therefor you can use "new" keyword for memory

correct program is here


#include<string>

using namespace std;

char* substring (char *s, int start, int end);

int main()
{
char *s="university";
char *ans;
//int start, end;

ans=substring(s, 2, 5);
cout<<ans<<endl;

system("pause");
return 0;

}

char* substring (char *s, int start, int end)
{
char *ptr=new char[end-start+1];
for(int i=0;i<(end-start); i++)
{
*(ptr+i)=*(s+i+start);
}
*(ptr+end-start)='\0';
return ptr;
}

[ami1234]

I dnt understand how the 2nd index gets the NULL, can u explain tht further, would be highly appreciated!! Thank yoooou!!