The **_crtDbgFlag** flag consists of five bit fields that control how memory allocations on the debug version of the heap are tracked, verified, reported, and dumped. The bit fields of the flag are set using the [_CrtSetDbgFlag](../c-runtime-library/reference/crtsetdbgflag.md) function. This flag and its bit fields are declared in Crtdbg.h. This flag is only available when the [_DEBUG](../c-runtime-library/debug.md) flag has been defined in the application.

For more information about using this flag in conjunction with other debug functions, see [Heap State Reporting Functions](/visualstudio/debugger/crt-debug-heap-details).

|[_aligned_malloc_dbg](../c-runtime-library/reference/aligned-malloc-dbg.md)|Allocates memory on a specified alignment boundary with additional space for a debugging header and overwrite buffers (debug version only).|

These routines convert data from one form to another. Generally these routines execute faster than conversions you might write. Each routine that begins with a *to* prefix is implemented as a function and as a macro. See [Choosing Between Functions and Macros](../c-runtime-library/recommendations-for-choosing-between-functions-and-macros.md) for information about choosing an implementation.

They are declared in Time.h as follows.

On a call to `_ftime`, `localtime`, or `_tzset`, the values of `_daylight`, `_dstbias`, `_timezone`, and `_tzname` are determined from the value of the `TZ` environment variable. If you do not explicitly set the value of `TZ`, `_tzname[0]` and `_tzname[1]` contain the default settings of "PST" and "PDT" respectively. The time-manipulation functions ([_tzset](../c-runtime-library/reference/tzset.md), [_ftime](../c-runtime-library/reference/ftime-ftime32-ftime64.md), and [localtime](../c-runtime-library/reference/localtime-localtime32-localtime64.md)) attempt to set the values of `_daylight`, `_dstbias` and `_timezone` by querying the operating system for the default value of each variable. The time-zone global variable values are shown in the following table.

| [`_calloc_dbg`](../c-runtime-library/reference/calloc-dbg.md) | Allocate a specified number of memory blocks on the heap with additional space for a debugging header and overwrite buffers |

| [`_malloc_dbg`](../c-runtime-library/reference/malloc-dbg.md) | Allocate a block of memory on the heap with additional space for a debugging header and overwrite buffers |

The debugger can be used to step through the source code for most of the C runtime routines during the debugging process. However, Microsoft considers some technology to be proprietary and, therefore, does not provide the source code for a subset of these routines. Most of these routines belong to either the exception handling or floating-point processing groups, but a few others are included as well. The following table lists these routines.

Although source code is available for most of the **printf** and **scanf** routines, they make an internal call to another routine for which source code is not provided.

Some C run-time functions and C++ operators behave differently when called from a debug build of an application. (Note that a debug build of an application can be done by either defining the `_DEBUG` flag or by linking with a debug version of the C run-time library.) The behavioral differences usually consist of extra features or information provided by the routine to support the debugging process. The following table lists these routines.

Beginning in Visual Studio 2013, the Universal C Runtime (UCRT) no longer supports the C++-specific operator new and operator delete functions. These are now part of the C++ Standard Library. For more information, see [new and delete operators](../cpp/new-and-delete-operators.md) and [delete operator](../cpp/delete-operator-cpp.md) in the C++ Language Reference.

The C run-time routines assume that the direction flag is cleared. If you are using other functions with the C run-time functions, you must ensure that the other functions leave the direction flag alone or restore it to its original condition. Expecting the direction flag to be clear upon entry makes the run-time code faster and more efficient.

*func*<br/>

*pbegin*<br/>

*pend*<br/>

The `__dllonexit` function is analogous to the [_onexit](../c-runtime-library/reference/onexit-onexit-m.md) function except that the global variables used by that function are not visible to this routine. Instead of global variables, this function uses the `pbegin` and `pend` parameters.