Member Avatar for meetjatin88

Hello Everyone i am trying to write a program for printing all the combinations of a string.I do not want any help regarding the algorithm but i need help figuring out why this program is giving the error message
"First-chance exception at 0x761bc41f in word.exe: Microsoft C++ exception: std::out_of_range at memory location 0x0026f6b4..
Unhandled exception at 0x761bc41f in word.exe: Microsoft C++ exception: std::out_of_range at memory location 0x0026f6b4.." when i try to run this in MVS 2010

#include<iostream>
#include <stdio.h>
#include <string>
#include <stdlib.h>
#include<conio.h>
void combination(std::string input,int length,std::string buffer,int allowedno)
{
    for(int i =allowedno;i<length;i++)
    {
        buffer.at(i)=input.at(i);
        std::cout << buffer<< '\n';
        if(i!=length)
        {
        combination(input,length,buffer,i+1);
        }
        buffer.erase(length-1);
    }
}

void combine(std::string input)
{
int length=input.size();
//char *buffer = (char *)malloc(sizeof(char)*(length+1));
std::string buffer(input);
buffer.erase();
combination(input,length,buffer,0);
}



void main()
{
    std ::string input= "ABC";
    combine(input);
   getch();
}
  • 3 Contributors
  • 3 Replies
  • 255 Views
  • 10 Hours Discussion Span
  • Latest Post Latest Post by meetjatin88

Dani AI

Generated

correctly pinpointed the cause: buffer is empty, so buffer.at(i) triggers std::out_of_range. std::string::at does bounds checking and will throw when the index is >= size(), which is exactly the exception seen.

A few safe ways to fix the code (pick one that matches the intended logic):

  • Pre-size the buffer when you intend to write by index: use buffer.resize(length); and then buffer[i] = .... Note: reserve(length) does not change size() and therefore does not make indexing safe.
  • Build the buffer incrementally and undo the append after recursion. This avoids indexed writes into an empty string. For example:
buffer.push_back(input[i]);
combination(input, length, buffer, i+1);
if (!buffer.empty()) buffer.pop_back();
  • Pass buffer by value into the recursive call so each recursion gets its own copy and no manual removal is required. That is simple and safe (at the cost of extra copies).

Also watch the buffer.erase(length-1) line: erase(pos) will throw out_of_range if pos > buffer.size(). Removing the last character should be done with pop_back() or resize(buffer.size()-1) after checking !buffer.empty().

As noted, wrapping development checks in a try/catch can make the problem easier to diagnose, but it is better to prevent invalid accesses in the first place. Small additional cleanups: use a standards-conformant int main() and avoid reliance on nonstandard conio.h/getch() if portability matters.

Recommended Answers

All 3 Replies

Member Avatar for Moschops

In the function combination buffer is of size zero. It is a string object that contains no characters. You then try to change the first character like this:
buffer.at(i)=input.at(i);
The first character does not exist so an exception is thrown.

Does VS2010 let you get away with compiling this code? It predates the 1998 C++ standard and by modern standards is bad code that should not compile.

Member Avatar for rubberman

What Moschops said. This is why we do exception handling (try/catch/throw) in C++. That will allow you to detect this sort of error and terminate after output of a meaningful error message that will help you fix the problem.

Member Avatar for meetjatin88

thanks you,i assume modifying the line to
buffer.append(input.at(i));
will fix the error.

Be a part of the DaniWeb community

We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, networking, learning, and sharing knowledge.