[RESOLVED] Why does this code leak memory?

Code:

// Check to see if the Found array needs to be expanded if (Entry > Max) { // Give the array 30 more spaces to fill Max += 30; /* Create a temp array with the amount of space desired, if the memory cannot be allocated return an error */ Temp = new POINT[Max]; if (!Temp) { delete [] Found; LastERR = FAILED_MALLOC; return NULL; } // Loop through the original and copy it to the new array for (int iCountARY = 0; iCountARY < Entry; iCountARY++) { Temp[iCountARY] = Found[iCountARY]; } // Release the old array delete [] Found; Found = Temp; }

I'm a beginner to C++ and am trying to check if a dynamic array needs to be expanded, and if so, expand it. But my compiler (Dev-C++) is giving me this warning

Code:

warning: heap block at 003F3CF8 modified at 003F3DF0 past requested size of f0

Which I think, after a little research, means that I was trying to access memory outside of my dynamic array or something along those lines. If anyone could quickly go over what I'm doing wrong I'd really appreciate it, thanks for reading!

Re: Why does this code leak memory?

arrays are zero indexed, so your conditional should be

Code:

if (Entry >= Max)

since your are allocating an array of size MAX.

I am not sure if that was clear so

POINT[5], contains 5 POINTS which you access with indices
0, 1, 2, 3, 4

using 5 for access will give the error you see

Re: Why does this code leak memory?

It doesn´t leak memory, you are accessing a memory location beyond array bonds. This will happen if (Entry +30) is larger than Max, because you resize your array by 30 instead of looking how many elements you´re gonna need. If you replace the line

Code:

// Give the array 30 more spaces to fill Max += 30;

by

[code]
// adjust array size to hold Entry elements
Max = Entry;
[/b]

or

Code:

while( Entry > Max ) { // resize array until it´s large enough to hold Entry elements Max = Max * 2; }

Maybe you can use std::vector instead?

Re: Why does this code leak memory?

Quote:

Originally Posted by Brownhead

I'm a beginner to C++ and am trying to check if a dynamic array needs to be expanded, and if so, expand it.

Use std::vector. Not only is it safer, it is much smarter and faster than using naked new[]/delete[] calls to do this.

Code:

#include <vector> int main() { std::vector<int> IntArray(10); // an array of 10 integers. IntArray.resize(20); // now it has 20 integers IntArray[0] = 10; // use just like a regular array }

There is your entire code in two lines.

Also, as mentioned before, what you're doing is slow compared to using vector and resize(). Believe me. I've timed code that looks like yours, and vector::resize() as opposed to using new[]/delete[] is many times faster because resize() has more intelligence than just doing straight new[] and delete[] calls each time the size changes.

Also, operator new[] does not return NULL if there is a failure. A conforming C++ compiler throws a std::bad_alloc exception if new fails.

Regards,

Paul McKenzie