OutputDebugStringA function (debugapi.h)

Sends a string to the debugger for display.


void OutputDebugStringA(
  [in, optional] LPCSTR lpOutputString


[in, optional] lpOutputString

The null-terminated string to be displayed.

Return value




To use this function, you must include the Windows.h header in your application (not debugapi.h).

In the past, the operating system did not return Unicode strings through OutputDebugStringW (ASCII strings were returned instead). To force OutputDebugStringW to return Unicode strings, debuggers are required to call the WaitForDebugEventEx function to opt into the new behavior. In this way, the operating system knows that the debugger supports Unicode and is specifically opting into receiving Unicode strings.

If the application does not have a debugger, and the filter mask allows it, the system debugger displays the string. To display the string, this function calls the DbgPrint function. Prior to Windows Vista, content was not filtered by the system debugger.

If the application does not have a debugger and the system debugger is not active, OutputDebugString does nothing.

OutputDebugStringW converts the specified string based on the current system locale information and passes it to OutputDebugStringA to be displayed. As a result, some Unicode characters may not be displayed correctly.

Applications should send very minimal debug output and provide a way for the user to enable or disable its use. See Event Tracing to learn more about tracing details.

Visual Studio has changed how it handles the display of these strings throughout its revision history. Refer to the Visual Studio documentation for details of how your version deals with this.

The debugapi.h header defines OutputDebugString as an alias that 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 is not encoding-neutral can lead to mismatches and compilation or runtime errors. For more information, see Conventions for Function Prototypes.


Requirement Value
Minimum supported client Windows XP [desktop apps | UWP apps]
Minimum supported server Windows Server 2003 [desktop apps | UWP apps]
Target Platform Windows
Header debugapi.h (include Windows.h)
Library Kernel32.lib
DLL Kernel32.dll

See also

Communicating with the Debugger, Debugging Functions