Deleting dynamic array of char in C++.

Question

I have this class, with the atribute 'word'

class Node {
    char *word;

Inside the Node constructor, I do this asignation:

word = new char[strlen(someword)];

In the destructor of the Node class, I try to delete the contents pointed by word:

delete []word;

I obtain the next message after executing the programs:

"Heap block at 003E4F48 modified at 003E4F51 past requested size of 1"

What am I not doing well?

Answer 1

strlen will return the length of the string but will not account for the null-terminating extra byte. My guess is that you are then copying in a string and appending a null-byte but you did not account for it when you originally allocated the memory. Try changing the code to read:

word = new char[strlen(someword) + 1];

Answer 2

You have a corrupt heap - somewhere else in your code you are writing outside the allocated memory or deleting something you shouldn't be - are you sure you don't mean strlen(someworrd) + 1?. The best solution to this problem is to use a std:;string or a std::vector rather than a dynamic array.

Answer 3

You have a buffer overflow in your program, somewhere else in code you didn't post. The problem is that you're not allocating enough memory -- you don't leave room for the null terminator at the end of your string. You should change the allocation to this:

word = new char[strlen(someword) + 1];  // +1 for null terminator
...
strcpy(word, someword);

You should be thankful your C runtime caught your error. In most cases, a one byte buffer overflow will result in silent memory corruption and not be detected until much later, if ever.

You should also consider using the std::string class, which automatically manages the memory for you, so you don't have to deal with subtle issues like this.