CapabilitiesRequestAndCapabilitiesReply function

Retrieves a string describing a monitor's capabilities.


_BOOL CapabilitiesRequestAndCapabilitiesReply(
  HANDLE hMonitor,
  LPSTR  pszASCIICapabilitiesString,
  DWORD  dwCapabilitiesStringLengthInCharacters



Handle to a physical monitor. To get the monitor handle, call GetPhysicalMonitorsFromHMONITOR or GetPhysicalMonitorsFromIDirect3DDevice9.


Pointer to a buffer that receives the monitor's capabilities string. The caller must allocate this buffer. To get the size of the string, call GetCapabilitiesStringLength. The capabilities string is always an ASCII string. The buffer must include space for the terminating null character.


Size of pszASCIICapabilitiesString in characters, including the terminating null character.

Return value

If the function succeeds, the return value is TRUE. If the function fails, the return value is FALSE. To get extended error information, call GetLastError.


This function corresponds to the "Capabilities Request & Capabilities Reply" command from the Display Data Channel Command Interface (DDC/CI) standard. For more information about the capabilities string, refer to the DDC/CI standard.

This function usually returns quickly, but sometimes it can take several seconds to complete.

You can update a monitor's capabilities string by adding an AddReg directive to the monitor's INF file. Add a registry key named "CapabilitiesString" to the monitor's driver key. The value of the registry key is the capabilities string. The registry data type is REG_SZ.

HKR,,"CapabilitiesString",0x00000000,"updated capabilities string"
Warning  Do not modify a monitor's INF file unless you are familiar with the layout of INF files and also understand the DDC/CI standard.


DWORD cchStringLength = 0;
BOOL bSuccess = 0;
LPSTR szCapabilitiesString = NULL;

// Get the length of the string.
bSuccess = GetCapabilitiesStringLength(
   hPhysicalMonitor, // Handle to the monitor.

if (bSuccess)
    // Allocate the string buffer.
    LPSTR szCapabilitiesString = (LPSTR)malloc(cchStringLength);
    if (szCapabilitiesString != NULL)
        // Get the capabilities string.
        bSuccess = CapabilitiesRequestAndCapabilitiesReply(

        // Free the string buffer.


Minimum supported client Windows Vista [desktop apps only]
Minimum supported server Windows Server 2008 [desktop apps only]
Target Platform Windows
Header lowlevelmonitorconfigurationapi.h
Library Dxva2.lib
DLL Dxva2.dll

See also

Monitor Configuration Functions