track C++ memory allocations

Question

Use Valgrind and its tool Massif. Its example output (a part of it):

99.48% (20,000B) (heap allocation functions) malloc/new/new[], --alloc-fns, etc.
->49.74% (10,000B) 0x804841A: main (example.c:20)
| 
->39.79% (8,000B) 0x80483C2: g (example.c:5)
| ->19.90% (4,000B) 0x80483E2: f (example.c:11)
| | ->19.90% (4,000B) 0x8048431: main (example.c:23)
| |   
| ->19.90% (4,000B) 0x8048436: main (example.c:25)
|   
->09.95% (2,000B) 0x80483DA: f (example.c:10)
  ->09.95% (2,000B) 0x8048431: main (example.c:23)

So, you will get detailed information:

• WHO allocated the memory (functions: g(), f(), and main() in above example); you also get complete backtrace leading to allocating function,
• to WHICH data structure the memory did go (no data structures in above example),
• WHEN it happened,
• what PERCENTAGE of all allocated memory it is (g: 39.7%, f: 9.95%, main: 49.7%).

Here is Massif manual

You can track heap allocation as well as stack allocation (turned off by default).

PS. I just read that you're on Windows. I will leave the answer though, because it gives a picture of what you can get from a possible tool.

Microsoft have well documented memory tracking functions. However, for some reason they are not really well-known in the developer community. These are CRT debug functions. Good starting point will be CRT Debug Heap functions.

Check the following links for more details

1. Heap state reporting functions
2. Tracking heap allocation requests. Probably this is the functionality that you are looking for.

For a generic C++ memory tracker you will need to overload the following:

global operator new
global operator new []
global operator delete
global operator delete []
any class allocators
any in-place allocators

The tricky bit is getting useful information, the overloaded operators only have size information for allocators and memory pointers for deletes. One answer is to use macros. I know. Nasty. An example - place in a header which is included from all source files:

#undef new

void *operator new (size_t size, char *file, int line, char *function);
// other operators

#define new new (__FILE__, __LINE__, __FUNCTION__)

and create a source file with:

void *operator new (size_t size, char *file, int line, char *function)
{
  // add tracking code here...
  return malloc (size);
}

The above only works if you don't have any operator new defined at class scope. If you do have some at class scope, do:

#define NEW new (__FILE__, __LINE__, __FUNCTION__)

and replace 'new type' with 'NEW type', but that requires changing a lot of code potentially.

As it's a macro, removing the memory tracker is quite straightforward, the header becomes:

#if defined ENABLED_MEMORY_TRACKER
#undef new

void *operator new (size_t size, char *file, int line, char *function);
// other operators

#define NEW new (__FILE__, __LINE__, __FUNCTION__)
#else
#define NEW new
#endif

and the implementation file:

#if defined ENABLED_MEMORY_TRACKER
void *operator new (size_t size, char *file, int line, char *function)
{
  // add tracking code here...
  return malloc (size);
}
endif

Update: to the answer of @Skizz

Since C++20, we can use std::source_location instead of macros like __FILE__ and __LINE__.

(As this is a major simplification, I believe that it deserves a seperate answer).