assertion failure when deleting pointer

[hansfordmc]

I'm getting an assertion failure error when I attempt to delete a pointer at the end of my code. If I remove the delete statement there is no error.Any idea why? Thanks

// strings.cpp : main project file.

#include "stdafx.h"
#include <iostream>
#include <string>

using namespace std;
using namespace System;

int main(array<System::String ^> ^args)
{
char* buffer = 0;
const int MAX = 100;
char first[MAX];
char last[MAX];
cout << endl << "Enter your first name: ";
cin.getline(first, MAX, '\n');
cout << endl << "Enter your last name: ";
cin.getline(last, MAX, '\n');
int size1 = strlen(first); 
int size2 = strlen(last);
const int finalsize = size1 + size2 + 2;

buffer = new char[finalsize];
const int sizeM = size1 + 1;
char* temp = new char[sizeM];

temp = first;
temp[size1] = ' ';
temp[size1 + 1] = '\0';
cout << temp << endl;
buffer = strcat(temp, last);
cout << endl << buffer << endl;
delete [] buffer;
buffer = NULL;
    return 0;
}

[btripp]

I think it is because you are deleting buffer on line 34 but on line 35 you are setting it to be a null pointer. You dont have to do that. Just call
delete [] buffer;

Also you have a memory leak. You also need to delete "temp" like the following
delete [] temp;

so just swap out buffer = NULL; with delete [] temp; and hopefully it fixes it.

Let me know if this solves your problems

[Disch]

because you're deleting 'first', which is a buffer you didn't allocate with new.

You're misinterpretting the assignment operator. Here's what's happening:

// line 24
buffer = new char[finalsize];  // GOOD - 'buffer' points to a newly allocated buffer

// line 26
char* temp = new char[sizeM];  // GOOD - 'temp' points to a newly allocated buffer

// line 28
temp = first;  // BAD - temp no longer points to your allocated buffer.  Now it points to 'first'
  // ie, if you try to delete[] temp now, it's the same thing as doing delete[] first, which
  // is no good

// line 32
buffer = strcat(temp, last);  // BAD
// strcat returns a pointer to the destination buffer (temp)
//  so now 'buffer', 'temp', and 'first' all point to the same memory.  You also lost your allocated buffers
//  so they are impossible to delete at this point. 

EDIT

Just to clarify... when dealing with C strings (char arrays), the = operator does NOT copy the string like you may expect. Instead, it changes what the pointer points to.

/EDIT

If you want to copy a C string, use strcpy:

// temp = first;  // bad
strcpy(temp,first); // good

//-----
//buffer = strcat(temp,last); // bad

strcpy(buffer,temp);
strcat(buffer,last);  // good 

or... save yourself the headache and just use std::string. Problems like this disappear and you don't have to worry about memory leaks or buffer overflows:

//char first[MAX];  // get rid of these C strings
//char last[MAX];

string first; // replace with C++ strings
string last;

// now you can use assignment, and +=, and all that other good stuff
//  and it'll work like you expect:

string fullname = first + " " + last;

[hansfordmc]

thanks Disch - that is much easier and you explained it perfectly.