DbgPrintEx function (wdm.h)

The DbgPrintEx routine sends a string to the kernel debugger if the conditions you specify are met.


  [in] ULONG ComponentId,
  [in] ULONG Level,
  [in] PCSTR Format,


[in] ComponentId

Specifies the component calling this routine. This must be one of the component name filter IDs defined in the Dpfilter.h header file. To avoid mixing your driver's output with the output of Windows components, you should use only the following values for ComponentId:


[in] Level

Specifies the severity of the message being sent. This can be any 32-bit integer. Values between 0 and 31 (inclusive) are treated differently than values between 32 and 0xFFFFFFFF. For details, see Reading and Filtering Debugging Messages.

[in] Format

Specifies a pointer to the format string to print. The Format string supports most of the printf-style format specification fields. However, the Unicode format codes (%C, %S, %lc, %ls, %wc, %ws, and %wZ) can only be used with IRQL = PASSIVE_LEVEL. The DbgPrintEx routine does not support any of the floating point types (%f, %e, %E, %g, %G, %a, or %A).


Specifies arguments for the format string, as in printf.

Return value

If successful, DbgPrintEx returns the NTSTATUS code STATUS_SUCCESS; otherwise, it returns the appropriate error code.


Only kernel-mode drivers can call the DbgPrintEx routine.

DbgPrint and DbgPrintEx can be called at IRQL<=DIRQL. However, Unicode format codes (%wc and %ws) can be used only at IRQL = PASSIVE_LEVEL. Also, because the debugger uses interprocess interrupts (IPIs) to communicate with other processors, calling DbgPrint at IRQL>DIRQL can cause deadlocks.

DbgPrintEx either passes the specified string to the kernel debugger or does nothing at all, depending on the values of ComponentId, Level, and the corresponding component filter masks. For details, see Reading and Filtering Debugging Messages.

Unless it is absolutely necessary, you should not obtain a string from user input or another process and pass it to DbgPrintEx. If you do use a string that you did not create, you must verify that this is a valid format string, and that the format codes match the argument list in type and quantity. The best coding practice is for all Format strings to be static and defined at compile time.

There is no upper limit to the size of the Format string or the number of arguments. However, any single call to DbgPrintEx will only transmit 512 bytes of information. There is also a limit to the size of the DbgPrint buffer. See The DbgPrint Buffer and the Debugger for details.


Requirement Value
Minimum supported client Available in Microsoft Windows XP and later.
Target Platform Universal
Header wdm.h (include Wdm.h)
Library NtDll.lib (user mode); NtosKrnl.lib (kernel mode)
DLL NtDll.dll (user mode); NtosKrnl.exe (kernel mode)
IRQL <= DIRQL (see Comments section)

See also