acmDriverMessage function (msacm.h)

Article
06/24/2021

The acmDriverMessage function sends a user-defined message to a given ACM driver instance.

Syntax

LRESULT ACMAPI acmDriverMessage(
  HACMDRIVER had,
  UINT       uMsg,
  LPARAM     lParam1,
  LPARAM     lParam2
);

Parameters

had

Handle to the ACM driver instance to which the message will be sent.

uMsg

Message that the ACM driver must process. This message must be in the ACMDM_USER message range (above or equal to ACMDM_USER and less than ACMDM_RESERVED_LOW). The exceptions to this restriction are the ACMDM_DRIVER_ABOUT, DRV_QUERYCONFIGURE, and DRV_CONFIGURE messages.

lParam1

Message parameter.

lParam2

Message parameter.

Return value

The return value is specific to the user-defined ACM driver message specified by the uMsg parameter. However, possible error values include the following.

Return code	Description
MMSYSERR_INVALHANDLE	The specified handle is invalid.
MMSYSERR_INVALPARAM	The uMsg parameter is not in the ACMDM_USER range.
MMSYSERR_NOTSUPPORTED	The ACM driver did not process the message.

Remarks

To display a custom About dialog box from an ACM driver, an application must send the ACMDM_DRIVER_ABOUT message to the driver. The lParam1 parameter should be the handle of the owner window for the custom About dialog box, and lParam2 must be set to zero. If the driver does not support a custom About dialog box, MMSYSERR_NOTSUPPORTED will be returned and it is the application's responsibility to display its own dialog box. For example, the Control Panel Sound Mapper option will display a default About dialog box based on the ACMDRIVERDETAILS structure when an ACM driver returns MMSYSERR_NOTSUPPORTED. An application can query a driver for custom About dialog box support without the dialog box being displayed by setting lParam1 to –1L. If the driver supports a custom About dialog box, MMSYSERR_NOERROR will be returned. Otherwise, the return value is MMSYSERR_NOTSUPPORTED.

User-defined messages must be sent only to an ACM driver that specifically supports the messages. The caller should verify that the ACM driver is the correct driver by retrieving the driver details and checking the wMid, wPid, and vdwDriver members of the ACMDRIVERDETAILS structure.

Never send user-defined messages to an unknown ACM driver.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	msacm.h
Library	Msacm32.lib
DLL	Msacm32.dll