C++ malloc error

I'm a Java programmer, but now I have to write a little bit of code in c++. I learned the basics of C++ a couple of years ago, so I'm not really fit.

I wrote a little class which describes a Polynomial. Here it is:

#include "Polynom.h"
#include <iostream>

using namespace std;

Polynom::Polynom()
{
    this->degree = 0;
    this->coeff = new int[0];
}

Polynom::Polynom(int degree)
{
    this->degree = degree;
    this->coeff = new int[degree + 1];
}

Polynom::~Polynom()
{
    delete coeff;
}

void Polynom::setDegree(int degree)
{
    this->degree = degree;
}

void Polynom::setCoeffs(int* coeff)
{
    this->coeff = &*coeff;
}

void Polynom::print()
{
    int i;
    for(i = degree; i >= 0; i --)
    {
        cout<<this->coeff[i];
        if(i != 0)
            cout<<"x^"<<i;
        if(i > 0)
        {
            if(coeff开发者_开发百科[i - 1] < 0)
                cout<<" - ";
            else
                cout<<" + ";
        }
    }    
}

Okay, now I tried to read the degree and the coefficients of the polynomial and print it in the console. Here's the code for that:

#include <iostream>
#include "Polynom.h"
using namespace std;

int main()
{
    int degree;

    cout<<"degree = ";
    cin>>degree;
    int* coeff = new int[degree];
    int i;
    for(i = 0; i <= degree; i++)
    {
        cout<<"coeff[x^"<<i<<"] = ";
        cin>>coeff[i];
    }
    Polynom *poly = new Polynom(degree);
    //poly->setDegree(degree);
    poly->setCoeffs(coeff);
    cout<<"The input polynome is: ";
    poly->print();
    return 0;
}

When compiling the code, everything is ok. When running, if I give an even degree and then give some coefficients, the program runs normally. But: if I define an odd degree (for example 3 or 5) and then give the coefficients, the program does not print the polynome and returns the following error:

malloc.c:3096: sYSMALLOc: Assertion `(old_top == (((mbinptr) (((char *) &((av)->bins[((1) - 1) * 2])) - __builtin_offsetof (struct malloc_chunk, fd)))) && old_size == 0) || ((unsigned long) (old_size) >= (unsigned long)((((__builtin_offsetof (struct malloc_chunk, fd_nextsize))+((2 * (sizeof(size_t))) - 1)) & ~((2 * (sizeof(size_t))) - 1))) && ((old_top)->size & 0x1) && ((unsigned long)old_end & pagemask) == 0)' failed.

Why does this happen? Where didn't I allocate enough memory for the array? I googled for this error and stumbled upon this page, but the solution mentioned there did not help me much.

Maybe you can see another problem in my code? I would really appreciate your help.

Thanks in advance.

There is a vast amount wrong with your code. C++ is nothing like Java and it seems that you are using pointers as if they are like references in Java, which they emphatically are not.

Polynom::Polynom()
{
    this->degree = 0;
    this->coeff = new int[0];
}

This creates an array of size zero, which is legal in C++, but almost never what you want.

Polynom::~Polynom()
{
    delete coeff;
}

Arrays in C++ must be deleted with delete[]:

Polynom::~Polynom()
{
    delete [] coeff;
}

This:

void Polynom::setDegree(int degree)
{
    this->degree = degree;
}

makes no sense - you change the degree, but not the array it is associated with.

void Polynom::setCoeffs(int* coeff)
{
    this->coeff = &*coeff;
}

I have no idea what you think this is doing, and I suspect you don't either. And you have a memory leak.

That was just for starters - Isuspect there is much more bad stuff. You need to do two things:

• Read a book on C++. As you have programming experience, I recommend Accelerated C++.

• Forget about your Java knowledge. As I said, the two languages have almost nothing in common.

int* coeff = new int[degree];
int i;
for(i = 0; i <= degree; i++)

You are allocating space for degree elements and putting there degree+1 elements... The behavior is undefined.

In your main() function, int *coeff = new int[degree] gives you a length-degree array, with element indices ranging from 0 to degree-1, inclusive. In your loop, you are accessing elements 0 to degree, inclusive. This is undefined behaviour, which may or may not cause runtime errors, etc.

The statement i <= degree in the for loop is causing it. Since array indexes start from 0 the valid range is 0->degree-1. Since you are writing to an invalid memory location your program is behaving unpredictably.