使用方法非常简单，首先定义宏_CRTDBG_MAP_ALLOC，然后包含头文件crtdbg.h，最后在main函数结尾调用_CrtDumpMemoryLeaks统计内存申请和释放的情况。相关例子如下，编译的时候需要在Debug模式：
运行结果如下:
在安装Visual Studio之后，Windows CRT的源码已经被存放在C:\Program Files (x86)\Windows Kits\10\Source\，这个目录下面有多个sdk的版本，我选择的是19041。
在C++编程语言中，内存申请对应的关键字是new或malloc，其实new最后调用的也是malloc函数，对应源代码文件是debug_heap.cpp。在包含相关头文件之后，malloc函数的调用栈为：malloc -> _malloc_dbg -> heap_alloc_dbg -> heap_alloc_dbg_internal。heap_alloc_dbg_internal函数分析如下：
_pfnAllocHook有一个默认的回调函数，也允许程序员自己定义，回调函数原型如下:
设置回调函数的接口为_CrtSetAllocHook.
3. 调用Windows API分配内存，不过需要多分配一些冗余内存，记录一些信息，用于管理malloc分配的内存。
管理的数据结构如下：
结构中成员_gap填充了no_mans_land_size(4)个0xFD，在释放内存时检测写内存时是否出现溢出(上溢)。该结构后续的内容是malloc返回的内存，内存中被填充了0xCD。最后内存_another_gap也是填充了no_mans_land_size(4)个0xFD，在释放内存时检测写内存时是否出现溢出(下溢)。
在C++编程语言中，内存扩容的关键字为realloc，对应的源文件是realloc.cpp，realloc函数的调用栈为：realloc -> _realloc_dbg -> realloc_dbg_nolock。该函数的函数原型如下：
在C++编程语言中，内存释放对应的关键字是delete或free，delete操作符最后调用到free函数，对应的源文件是debug_heap.cpp。
free函数的调用栈为：free -> _free_dbg -> free_dbg_nolock，_free_dbg函数会获取临界区然后调用free_dbg_nolock。free_dbg_nolock函数分析过程如下：
调用_CrtDumpMemoryLeaks进行内存统计，主要是两个函数：_CrtMemCheckpoint(统计)和_CrtMemDumpAllObjectsSince(显示)
#define _CRTDBG_MAP_ALLOC
#include <stdlib.h>
#include <crtdbg.h>
#include <iostream>
int main()
{
std::cout << "Hello World!\n";
int* x = (int*)malloc(sizeof(int));
*x = 7;
printf("%d\n", *x);
x = (int*)calloc(3, sizeof(int));
x[0] = 7;
x[1] = 77;
x[2] = 777;
printf("%d %d %d\n", x[0], x[1], x[2]);
_CrtSetReportMode(_CRT_WARN, _CRTDBG_MODE_DEBUG);
_CrtDumpMemoryLeaks();
}
#define _CRTDBG_MAP_ALLOC
#include <stdlib.h>
#include <crtdbg.h>
#include <iostream>
int main()
{
std::cout << "Hello World!\n";
int* x = (int*)malloc(sizeof(int));
*x = 7;
printf("%d\n", *x);
x = (int*)calloc(3, sizeof(int));
x[0] = 7;
x[1] = 77;
x[2] = 777;
printf("%d %d %d\n", x[0], x[1], x[2]);
_CrtSetReportMode(_CRT_WARN, _CRTDBG_MODE_DEBUG);
_CrtDumpMemoryLeaks();
}
Detected memory leaks!
Dumping objects ->
main.cpp(16) : {163} normal block at 0x000002882AE17740, 12 bytes long.
Data: < M > 07 00 00 00 4D 00 00 00 09 03 00 00
main.cpp(10) : {162} normal block at 0x000002882AE148C0, 4 bytes long.
Data: < > 07 00 00 00
Object dump complete.
Detected memory leaks!
Dumping objects ->
main.cpp(16) : {163} normal block at 0x000002882AE17740, 12 bytes long.
Data: < M > 07 00 00 00 4D 00 00 00 09 03 00 00
main.cpp(10) : {162} normal block at 0x000002882AE148C0, 4 bytes long.
Data: < > 07 00 00 00
Object dump complete.
__acrt_lock(__acrt_heap_lock);
extern "C" void __cdecl __acrt_lock(_In_ __acrt_lock_id _Lock)
{
EnterCriticalSection(&__acrt_lock_table[_Lock]);
}
__acrt_lock(__acrt_heap_lock);
extern "C" void __cdecl __acrt_lock(_In_ __acrt_lock_id _Lock)
{
EnterCriticalSection(&__acrt_lock_table[_Lock]);
}
if (_crtBreakAlloc != -1 && request_number == _crtBreakAlloc)
{
_CrtDbgBreak();
}
if (_pfnAllocHook && !_pfnAllocHook(
_HOOK_ALLOC,
nullptr,
size,
block_use,
request_number,
reinterpret_cast<unsigned char const*>(file_name),
line_number))
{
if (file_name)
_RPTN(_CRT_WARN, "Client hook allocation failure at file %hs line %d.\n", file_name, line_number);
else
_RPT0(_CRT_WARN, "Client hook allocation failure.\n");
__leave;
}
if (_crtBreakAlloc != -1 && request_number == _crtBreakAlloc)
{
_CrtDbgBreak();
}
if (_pfnAllocHook && !_pfnAllocHook(
_HOOK_ALLOC,
nullptr,
size,
block_use,
request_number,
reinterpret_cast<unsigned char const*>(file_name),
line_number))
{
if (file_name)
_RPTN(_CRT_WARN, "Client hook allocation failure at file %hs line %d.\n", file_name, line_number);
else
_RPT0(_CRT_WARN, "Client hook allocation failure.\n");
__leave;
}
typedef int (__cdecl * _CRT_ALLOC_HOOK)(
int const allocation_type,
void* const data,
size_t const size,
int const block_use,
long const request,
unsigned char const* const file_name,
int const line_number
);
typedef int (__cdecl * _CRT_ALLOC_HOOK)(
int const allocation_type,
void* const data,
size_t const size,
int const block_use,
long const request,
unsigned char const* const file_name,
int const line_number
);
struct _CrtMemBlockHeader
{
_CrtMemBlockHeader* _block_header_next;
_CrtMemBlockHeader* _block_header_prev;
char const* _file_name;
int _line_number;
int _block_use;
size_t _data_size;
long _request_number;
unsigned char _gap[no_mans_land_size];
};
struct _CrtMemBlockHeader
{
_CrtMemBlockHeader* _block_header_next;
_CrtMemBlockHeader* _block_header_prev;
char const* _file_name;
int _line_number;
int _block_use;
size_t _data_size;
long _request_number;
unsigned char _gap[no_mans_land_size];
};
static void * __cdecl realloc_dbg_nolock(
void* const block,
size_t* const new_size,
int const block_use,
char const* const file_name,
int const line_number,
bool const reallocation_is_allowed
) throw()
static void * __cdecl realloc_dbg_nolock(
void* const block,
size_t* const new_size,
int const block_use,
char const* const file_name,
int const line_number,
bool const reallocation_is_allowed
) throw()
if (!block)
{
return _malloc_dbg(*new_size, block_use, file_name, line_number);
}
if (reallocation_is_allowed && *new_size == 0)
{
_free_dbg(block, block_use);
return nullptr;
}
if (!block)
{
return _malloc_dbg(*new_size, block_use, file_name, line_number);
}
if (reallocation_is_allowed && *new_size == 0)
{
_free_dbg(block, block_use);
return nullptr;
}
if (_pfnAllocHook && !_pfnAllocHook(
_HOOK_REALLOC,
block,
*new_size,
block_use,
request_number,
reinterpret_cast<unsigned char const*>(file_name),
line_number))
{
if (file_name)
_RPTN(_CRT_WARN, "Client hook re-allocation failure at file %hs line %d.\n", file_name, line_number);
else
_RPT0(_CRT_WARN, "Client hook re-allocation failure.\n");
return nullptr;
}
if (_pfnAllocHook && !_pfnAllocHook(
_HOOK_REALLOC,
block,
*new_size,
block_use,
request_number,
reinterpret_cast<unsigned char const*>(file_name),
line_number))
{
if (file_name)
_RPTN(_CRT_WARN, "Client hook re-allocation failure at file %hs line %d.\n", file_name, line_number);
else
_RPT0(_CRT_WARN, "Client hook re-allocation failure.\n");
return nullptr;
}
is_block_an_aligned_allocation(block)
_ASSERTE(_CrtIsValidHeapPointer(block));
检查 -> 堆的类型是否是_IGNORE_BLOCK
检查 -> block的header的_data_size是否被破坏
检查 -> *new_size 是否过大
if (*new_size > static_cast<size_t>(_HEAP_MAXREQ - no_mans_land_size - sizeof(_CrtMemBlockHeader)))
{
errno = ENOMEM;
return nullptr;
}
is_block_an_aligned_allocation(block)
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