CreateToolhelp32Snapshot function (tlhelp32.h)

Article
10/13/2021

Takes a snapshot of the specified processes, as well as the heaps, modules, and threads used by these processes.

Syntax

HANDLE CreateToolhelp32Snapshot(
  [in] DWORD dwFlags,
  [in] DWORD th32ProcessID
);

Parameters

[in] dwFlags

The portions of the system to be included in the snapshot. This parameter can be one or more of the following values.

Value	Meaning
TH32CS_INHERIT 0x80000000	Indicates that the snapshot handle is to be inheritable.
TH32CS_SNAPALL	Includes all processes and threads in the system, plus the heaps and modules of the process specified in th32ProcessID. Equivalent to specifying the TH32CS_SNAPHEAPLIST, TH32CS_SNAPMODULE, TH32CS_SNAPPROCESS, and TH32CS_SNAPTHREAD values combined using an OR operation ('\|').
TH32CS_SNAPHEAPLIST 0x00000001	Includes all heaps of the process specified in th32ProcessID in the snapshot. To enumerate the heaps, see Heap32ListFirst.
TH32CS_SNAPMODULE 0x00000008	Includes all modules of the process specified in th32ProcessID in the snapshot. To enumerate the modules, see Module32First. If the function fails with ERROR_BAD_LENGTH, retry the function until it succeeds. 64-bit Windows: Using this flag in a 32-bit process includes the 32-bit modules of the process specified in th32ProcessID, while using it in a 64-bit process includes the 64-bit modules. To include the 32-bit modules of the process specified in th32ProcessID from a 64-bit process, use the TH32CS_SNAPMODULE32 flag.
TH32CS_SNAPMODULE32 0x00000010	Includes all 32-bit modules of the process specified in th32ProcessID in the snapshot when called from a 64-bit process. This flag can be combined with TH32CS_SNAPMODULE or TH32CS_SNAPALL. If the function fails with ERROR_BAD_LENGTH, retry the function until it succeeds.
TH32CS_SNAPPROCESS 0x00000002	Includes all processes in the system in the snapshot. To enumerate the processes, see Process32First.
TH32CS_SNAPTHREAD 0x00000004	Includes all threads in the system in the snapshot. To enumerate the threads, see Thread32First. To identify the threads that belong to a specific process, compare its process identifier to the th32OwnerProcessID member of the THREADENTRY32 structure when enumerating the threads.

[in] th32ProcessID

The process identifier of the process to be included in the snapshot. This parameter can be zero to indicate the current process. This parameter is used when the TH32CS_SNAPHEAPLIST, TH32CS_SNAPMODULE, TH32CS_SNAPMODULE32, or TH32CS_SNAPALL value is specified. Otherwise, it is ignored and all processes are included in the snapshot.

If the specified process is the Idle process or one of the CSRSS processes, this function fails and the last error code is ERROR_ACCESS_DENIED because their access restrictions prevent user-level code from opening them.

If the specified process is a 64-bit process and the caller is a 32-bit process, this function fails and the last error code is ERROR_PARTIAL_COPY (299).

Return value

If the function succeeds, it returns an open handle to the specified snapshot.

If the function fails, it returns INVALID_HANDLE_VALUE. To get extended error information, call GetLastError. Possible error codes include ERROR_BAD_LENGTH.

Remarks

The snapshot taken by this function is examined by the other tool help functions to provide their results. Access to the snapshot is read only. The snapshot handle acts as an object handle and is subject to the same rules regarding which processes and threads it is valid in.

To enumerate the heap or module states for all processes, specify TH32CS_SNAPALL and set th32ProcessID to zero. Then, for each additional process in the snapshot, call CreateToolhelp32Snapshot again, specifying its process identifier and the TH32CS_SNAPHEAPLIST or TH32_SNAPMODULE value.

When taking snapshots that include heaps and modules for a process other than the current process, the CreateToolhelp32Snapshot function can fail or return incorrect information for a variety of reasons. For example, if the loader data table in the target process is corrupted or not initialized, or if the module list changes during the function call as a result of DLLs being loaded or unloaded, the function might fail with ERROR_BAD_LENGTH or other error code. Ensure that the target process was not started in a suspended state, and try calling the function again. If the function fails with ERROR_BAD_LENGTH when called with TH32CS_SNAPMODULE or TH32CS_SNAPMODULE32, call the function again until it succeeds.

The TH32CS_SNAPMODULE and TH32CS_SNAPMODULE32 flags do not retrieve handles for modules that were loaded with the LOAD_LIBRARY_AS_DATAFILE or similar flags. For more information, see LoadLibraryEx.

To destroy the snapshot, use the CloseHandle function.

Note that you can use the QueryFullProcessImageName function to retrieve the full name of an executable image for both 32- and 64-bit processes from a 32-bit process.

Examples

For an example, see Taking a Snapshot and Viewing Processes.

Requirements

Requirement	Value
Minimum supported client	Windows XP [desktop apps only]
Minimum supported server	Windows Server 2003 [desktop apps only]
Target Platform	Windows
Header	tlhelp32.h
Library	Kernel32.lib
DLL	Kernel32.dll

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