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DebugActiveProcess function

Enables a debugger to attach to an active process and debug it.


BOOL WINAPI DebugActiveProcess(
  _In_ DWORD dwProcessId


dwProcessId [in]

The identifier for the process to be debugged. The debugger is granted debugging access to the process as if it created the process with the DEBUG_ONLY_THIS_PROCESS flag. For more information, see the Remarks section of this topic.

Return value

If the function succeeds, the return value is nonzero.

If the function fails, the return value is 0 (zero). To get extended error information, call GetLastError.


To stop debugging the process, you must exit the process or call the DebugActiveProcessStop function. Exiting the debugger also exits the process unless you use the DebugSetProcessKillOnExit function.

The debugger must have appropriate access to the target process, and it must be able to open the process for PROCESS_ALL_ACCESS. DebugActiveProcess can fail if the target process is created with a security descriptor that grants the debugger anything less than full access. If the debugging process has the SE_DEBUG_NAME privilege granted and enabled, it can debug any process.

After the system checks the process identifier and determines that a valid debugging attachment is being made, the function returns TRUE. Then the debugger is expected to wait for debugging events by using the WaitForDebugEvent function. The system suspends all threads in the process, and sends the debugger events that represents the current state of the process.

The system sends the debugger a single CREATE_PROCESS_DEBUG_EVENT debugging event that represents the process specified by the dwProcessId parameter. The lpStartAddress member of the CREATE_PROCESS_DEBUG_INFO structure is NULL.

For each thread that is currently part of the process, the system sends a CREATE_THREAD_DEBUG_EVENT debugging event. The lpStartAddress member of the CREATE_THREAD_DEBUG_INFO structure is NULL.

For each dynamic-link library (DLL) that is currently loaded into the address space of the target process, the system sends a LOAD_DLL_DEBUG_EVENT debugging event. The system arranges for the first thread in the process to execute a breakpoint instruction after it resumes. Continuing this thread causes it to return to doing the same thing as before the debugger is attached.

After all of this is done, the system resumes all threads in the process. When the first thread in the process resumes, it executes a breakpoint instruction that causes an EXCEPTION_DEBUG_EVENT debugging event to be sent to the debugger. All future debugging events are sent to the debugger by using the normal mechanism and rules.


Minimum supported client

Windows XP [desktop apps only]

Minimum supported server

Windows Server 2003 [desktop apps only]


WinBase.h (include Windows.h)





See also

Debugging a Running Process
Debugging Functions