`_CrtReportBlockType`

Article
02/07/2023

Returns the block type/subtype associated with a given debug heap block pointer.

Syntax

int _CrtReportBlockType(
   const void * pBlock
};

Parameters

pBlock
Pointer to a valid debug heap block.

Return value

When passed a valid debug heap pointer, the _CrtReportBlockType function returns the block type and subtype in the form of an int. When passed an invalid pointer, the function returns -1.

Remarks

To extract the type and subtype returned by _CrtReportBlockType, use the macros _BLOCK_TYPE and _BLOCK_SUBTYPE (both defined in Crtdbg.h) on the return value.

For information about the allocation block types and how they're used, see Types of blocks on the debug heap.

Requirements

Routine	Required header
`_CrtReportBlockType`	<crtdbg.h>

For more compatibility information, see Compatibility.

Libraries

Debug versions of C run-time libraries only.

Example

// crt_crtreportblocktype.cpp
// compile with: /MDd

#include <malloc.h>
#include <stdio.h>
#include <crtdbg.h>

void __cdecl Dumper(void *ptr, void *)
{
    int block = _CrtReportBlockType(ptr);
    _RPT3(_CRT_WARN, "Dumper found block at %p: type %d, subtype %d\n", ptr,
          _BLOCK_TYPE(block), _BLOCK_SUBTYPE(block));
}

void __cdecl LeakDumper(void *ptr, size_t sz)
{
    int block = _CrtReportBlockType(ptr);
    _RPT4(_CRT_WARN, "LeakDumper found block at %p:"
                     " type %d, subtype %d, size %d\n", ptr,
          _BLOCK_TYPE(block), _BLOCK_SUBTYPE(block), sz);
}

int main(void)
{
    _CrtSetDbgFlag(_CrtSetDbgFlag(_CRTDBG_REPORT_FLAG) |
    _CRTDBG_LEAK_CHECK_DF);
    _CrtSetReportMode( _CRT_WARN, _CRTDBG_MODE_FILE );
    _CrtSetReportFile( _CRT_WARN, _CRTDBG_FILE_STDOUT );
    _malloc_dbg(10, _NORMAL_BLOCK , __FILE__, __LINE__);
    _malloc_dbg(10, _CLIENT_BLOCK | (1 << 16), __FILE__, __LINE__);
    _malloc_dbg(20, _CLIENT_BLOCK | (2 << 16), __FILE__, __LINE__);
    _malloc_dbg(30, _CLIENT_BLOCK | (3 << 16), __FILE__, __LINE__);
    _CrtDoForAllClientObjects(Dumper, NULL);
    _CrtSetDumpClient(LeakDumper);
}

Sample output

Dumper found block at 00314F78: type 4, subtype 3
Dumper found block at 00314F38: type 4, subtype 2
Dumper found block at 00314F00: type 4, subtype 1
Detected memory leaks!
Dumping objects ->
crt_crtreportblocktype.cpp(30) : {55} client block at 0x00314F78, subtype 3, 30 bytes long.
Data: <                > CD CD CD CD CD CD CD CD CD CD CD CD CD CD CD CD
crt_crtreportblocktype.cpp(29) : {54} client block at 0x00314F38, subtype 2, 20 bytes long.
Data: <                > CD CD CD CD CD CD CD CD CD CD CD CD CD CD CD CD
crt_crtreportblocktype.cpp(28) : {53} client block at 0x00314F00, subtype 1, 10 bytes long.
Data: <          > CD CD CD CD CD CD CD CD CD CD
crt_crtreportblocktype.cpp(27) : {52} normal block at 0x00314EC8, 10 bytes long.
Data: <          > CD CD CD CD CD CD CD CD CD CD
Object dump complete.

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