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Heap State Reporting Functions

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Several functions report the contents of the debug heap at a given moment.

To capture a summary snapshot of the state of the heap at a given time, use the _CrtMemState structure defined in CRTDBG.H:

typedef struct _CrtMemState
{
    // Pointer to the most recently allocated block:
    struct _CrtMemBlockHeader * pBlockHeader;
    // A counter for each of the 5 types of block:
    size_t lCounts[_MAX_BLOCKS];
    // Total bytes allocated in each block type:
    size_t lSizes[_MAX_BLOCKS];
    // The most bytes allocated at a time up to now:
    size_t lHighWaterCount;
    // The total bytes allocated at present:
    size_t lTotalCount;
} _CrtMemState;

This structure saves a pointer to the first (most recently allocated) block in the debug heap's linked list. Then, in two arrays, it records how many of each type of memory block (_NORMAL_BLOCK, _CLIENT_BLOCK, _FREE_BLOCK, and so on) are in the list and the number of bytes allocated in each type of block. Finally, it records the highest number of bytes allocated in the heap as a whole up to that point, and the number of bytes currently allocated.

The following functions report the state and contents of the heap, and use the information to help detect memory leaks and other problems.

Function

Description

_CrtMemCheckpoint

Saves a snapshot of the heap in a _CrtMemState structure supplied by the application.

_CrtMemDifference

Compares two memory state structures, saves the difference between them in a third state structure, and returns TRUE if the two states are different.

_CrtMemDumpStatistics

Dumps a given _CrtMemState structure. The structure may contain a snapshot of the state of the debug heap at a given moment or the difference between two snapshots.

_CrtMemDumpAllObjectsSince

Dumps information about all objects allocated since a given snapshot was taken of the heap or from the start of execution. Every time it dumps a _CLIENT_BLOCK block, it calls a hook function supplied by the application, if one has been installed using _CrtSetDumpClient.

_CrtDumpMemoryLeaks

Determines whether any memory leaks occurred since the start of program execution and, if so, dumps all allocated objects. Every time _CrtDumpMemoryLeaks dumps a _CLIENT_BLOCK block, it calls a hook function supplied by the application, if one has been installed using _CrtSetDumpClient.

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