I wrote the following heap debugger in order to demonstrate memory leaks, double deletes and wrong forms of deletes (i.e. trying to delete an array with delete p instead of delete[] p) to beginning programmers.
I would love to get some feedback on that from strong C++ programmers because I have never done this before and I'm sure I've done some stupid mistakes. Thanks!
#include <cstdlib>
#include <iostream>
#include <new>
namespace
{
const int ALIGNMENT = 16;
const char* const ERR = "*** ERROR: ";
int counter = 0;
struct heap_debugger
{
heap_debugger()
{
std::cerr << "*** heap debugger started\n";
}
~heap_debugger()
{
std::cerr << "*** heap debugger shutting down\n";
if (counter > 0)
{
std::cerr << ERR << "failed to release memory " << counter << " times\n";
}
else if (counter < 0)
{
std::cerr << ERR << (-counter) << " double deletes detected\n";
}
}
} instance;
void* allocate(size_t size, const char* kind_of_memory, size_t token) throw (std::bad_alloc)
{
void* raw = malloc(size + ALIGNMENT);
if (raw == 0) throw std::bad_alloc();
*static_cast<size_t*>(raw) = token;
void* payload = static_cast<char*>(raw) + ALIGNMENT;
++counter;
std::cerr << "*** allocated " << kind_of_memory << " at " << payload << " (" << size << " bytes)\n";
return payload;
}
void release(void* payload, const char* kind_of_memory, size_t correct_token, size_t wrong_token) throw ()
{
if (payload == 0) return;
std::cerr << "*** releasing " << kind_of_memory << " at " << payload << '\n';
--counter;
void* raw = static_cast<char*>(payload) - ALIGNMENT;
size_t* token = static_cast<size_t*>(raw);
if (*token == correct_token)
{
*token = 0xDEADBEEF;
free(raw);
}
else if (*token == wrong_token)
{
*token = 0x177E6A7;
std::cerr << ERR << "wrong form of delete\n";
}
else
{
std::cerr << ERR << "double delete\n";
}
}
}
void* operator new(size_t size) throw (std::bad_alloc)
{
return allocate(size, "non-array memory", 0x5AFE6A8D);
}
void* operator new[](size_t size) throw (std::bad_alloc)
{
return allocate(size, " array memory", 0x5AFE6A8E);
}
void operator delete(void* payload) throw ()
{
release(payload, "non-array memory", 0x5AFE6A8D, 0x5AFE6A8E);
}
void operator delete[](void* payload) throw ()
{
release(payload, " array memory", 0x5AFE6A8E, 0x5AFE6A8D);
}
