PdhEnumObjectItemsA function (pdh.h)

Article
02/09/2023

Returns the specified object's counter and instance names that exist on the specified computer or in the specified log file.

To use handles to data sources, use the PdhEnumObjectItemsH function.

Syntax

PDH_FUNCTION PdhEnumObjectItemsA(
  [in]      LPCSTR  szDataSource,
  [in]      LPCSTR  szMachineName,
  [in]      LPCSTR  szObjectName,
  [out]     PZZSTR  mszCounterList,
  [in, out] LPDWORD pcchCounterListLength,
  [out]     PZZSTR  mszInstanceList,
  [in, out] LPDWORD pcchInstanceListLength,
  [in]      DWORD   dwDetailLevel,
  [in]      DWORD   dwFlags
);

Parameters

[in] szDataSource

Null-terminated string that specifies the name of the log file used to enumerate the counter and instance names. If NULL, the function uses the computer specified in

the szMachineName parameter to enumerate the names.

[in] szMachineName

Null-terminated string that specifies the name of the computer that contains the counter and instance names that you want to enumerate.

Include the leading slashes in the computer name, for example, \computername.

If the szDataSource parameter is NULL, you can set szMachineName to NULL to specify the local computer.

[in] szObjectName

Null-terminated string that specifies the name of the object whose counter and instance names you want to enumerate.

[out] mszCounterList

Caller-allocated buffer that receives a list of null-terminated counter names provided by the specified object. The list contains unique counter names. The list is terminated by two NULL characters. Set to NULL if the pcchCounterListLength parameter is zero.

[in, out] pcchCounterListLength

Size of the mszCounterList buffer, in TCHARs. If zero on input and the object exists, the function returns PDH_MORE_DATA and sets this parameter to the required buffer size. If the buffer is larger than the required size, the function sets this parameter to the actual size of the buffer that was used. If the specified size on input is greater than zero but less than the required size, you should not rely on the returned size to reallocate the buffer.

[out] mszInstanceList

Caller-allocated buffer that receives a list of null-terminated instance names provided by the specified object. The list contains unique instance names. The list is terminated by two NULL characters. Set to NULL if pcchInstanceListLength is zero.

[in, out] pcchInstanceListLength

Size of the mszInstanceList buffer, in TCHARs. If zero on input and the object exists, the function returns PDH_MORE_DATA and sets this parameter to the required buffer size. If the buffer is larger than the required size, the function sets this parameter to the actual size of the buffer that was used. If the specified size on input is greater than zero but less than the required size, you should not rely on the returned size to reallocate the buffer.

If the specified object does not support variable instances, then the returned value will be zero. If the specified object does support variable instances, but does not currently have any instances, then the value returned is 2, which is the size of an empty MULTI_SZ list string.

[in] dwDetailLevel

Detail level of the performance items to return. All items that are of the specified detail level or less will be returned (the levels are listed in increasing order). This parameter can be one of the following values.

Value	Meaning
PERF_DETAIL_NOVICE	Novice user level of detail.
PERF_DETAIL_ADVANCED	Advanced user level of detail.
PERF_DETAIL_EXPERT	Expert user level of detail.
PERF_DETAIL_WIZARD	System designer level of detail.

[in] dwFlags

This parameter must be zero.

Return value

If the function succeeds, it returns ERROR_SUCCESS.

If the function fails, the return value is a system error code or a PDH error code. The following are possible values.

Return code	Description
PDH_MORE_DATA	One of the buffers is too small to contain the list of names. This return value is expected if pcchCounterListLength or pcchInstanceListLength is zero on input. If the specified size on input is greater than zero but less than the required size, you should not rely on the returned size to reallocate the buffer.
PDH_INVALID_ARGUMENT	A parameter is not valid. For example, on some releases you could receive this error if the specified size on input is greater than zero but less than the required size.
PDH_MEMORY_ALLOCATION_FAILURE	Unable to allocate memory to support this function.
PDH_CSTATUS_NO_MACHINE	The specified computer is offline or unavailable.
PDH_CSTATUS_NO_OBJECT	The specified object could not be found on the specified computer or in the specified log file.

Remarks

You should call this function twice, the first time to get the required buffer size (set the buffers to NULL and the sizes to 0), and the second time to get the data.

Consecutive calls to this function will return identical lists of counters and instances, because PdhEnumObjectItems will always query the list of performance objects defined by the last call to PdhEnumObjects or PdhEnumObjectItems. To refresh the list of performance objects, call PdhEnumObjects with a bRefresh flag value of TRUE before calling PdhEnumObjectItems again.

The order of the instance and counter names is undetermined.

Examples

For an example, see Enumerating Process Objects.

Note

The pdh.h header defines PdhEnumObjectItems as an alias which automatically selects the ANSI or Unicode version of this function based on the definition of the UNICODE preprocessor constant. Mixing usage of the encoding-neutral alias with code that not encoding-neutral can lead to mismatches that result in compilation or runtime errors. For more information, see Conventions for Function Prototypes.

Requirements

Requirement	Value
Minimum supported client	Windows XP [desktop apps only]
Minimum supported server	Windows Server 2003 [desktop apps only]
Target Platform	Windows
Header	pdh.h
Library	Pdh.lib
DLL	Pdh.dll

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