Debug versions of heap allocation functions
The C runtime (CRT) library contains special Debug versions of the heap allocation functions. These functions have the same names as the Release versions with _dbg
appended to them. This article describes the differences between the Release version of a CRT function and the _dbg
version, using malloc
and _malloc_dbg
as examples.
When _DEBUG
is defined, the CRT maps all malloc
calls to _malloc_dbg
. Therefore, you don't need to rewrite your code using _malloc_dbg
instead of malloc
to receive the benefits while debugging.
You might want to call _malloc_dbg
explicitly, however. Calling _malloc_dbg
explicitly has some added benefits:
Tracking
_CLIENT_BLOCK
type allocations.Storing the source file and line number where the allocation request occurred.
If you don't want to convert your malloc
calls to _malloc_dbg
, you can obtain the source file information by defining _CRTDBG_MAP_ALLOC
, which causes the preprocessor to directly map all calls to malloc
to _malloc_dbg
instead of relying on a wrapper around malloc
.
To track the separate types of allocations in client blocks, you must call _malloc_dbg
directly and set the blockType
parameter to _CLIENT_BLOCK
.
When _DEBUG
isn't defined, calls to malloc
aren't disturbed, calls to _malloc_dbg
are resolved to malloc
, the definition of _CRTDBG_MAP_ALLOC
is ignored, and source file information pertaining to the allocation request isn't provided. Because malloc
doesn't have a block type parameter, requests for _CLIENT_BLOCK
types are treated as standard allocations.