When does #if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP) in dxvahd.h Microsoft header file become true

Question

Hi I am having 2 VC++ solutions "A" & "B" (VS2008) both are having the same codebase (with just few lines of code different). Using DXVAHD.h in both.

dxvahd.h is a standard Microsoft header file. If we open this header file, we see there is a conditional if "#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP)"

I see that in VC++ solution "A", the above conditional #if statement is false, hence the whole dxvahd header file gets greyed out & is not even compiled!!

Whereas in another solution "B", this conditional #if is true,hence no issues & its working fine.

Can anyone kindly let me know how do I resolve this issue in solution "A", wherein the above #if is getting greyed out / not compiling. PLz help me.

Thanks in advance.

Answer 1

Looking at winapifamily.h, you can see that these macros are used to determine what platform you have and what API's are suitable for your platform.

/*
 *  Windows APIs can be placed in a partition represented by one of the below bits.   The 
 *  WINAPI_FAMILY value determines which partitions are available to the client code.
 */

#define WINAPI_PARTITION_DESKTOP   0x00000001
#define WINAPI_PARTITION_APP       0x00000002    

/*
 * A family may be defined as the union of multiple families. WINAPI_FAMILY should be set
 * to one of these values.
 */
#define WINAPI_FAMILY_APP          WINAPI_PARTITION_APP
#define WINAPI_FAMILY_DESKTOP_APP  (WINAPI_PARTITION_DESKTOP | WINAPI_PARTITION_APP)    

/*
 * A constant that specifies which code is available to the program's target runtime platform.
 * By default we use the 'desktop app' family which places no restrictions on the API surface. 
 * To restrict the API surface to just the App API surface, define WINAPI_FAMILY to WINAPI_FAMILY_APP.
 */
#ifndef WINAPI_FAMILY
#define WINAPI_FAMILY WINAPI_FAMILY_DESKTOP_APP
#endif

/* Macro to determine if a partition is enabled */
#define WINAPI_FAMILY_PARTITION(Partition)  ((WINAPI_FAMILY & Partition) == Partition)

/* Macro to determine if only one partition is enabled from a set */
#define WINAPI_FAMILY_ONE_PARTITION(PartitionSet, Partition) ((WINAPI_FAMILY & PartitionSet) == Partition)

So your WINAPI_PARTITION_DESKTOP would only be set if you are running on a Desktop family of the the system.

Answer 2

WINAPI_FAMILY is also set depending on the targeted Windows version.

See this discussion and the linked blog post series.

In particular, if you're not writing an "App" (for >= Win 8) then:

Prefer use of the standard _WIN32_WINNT Windows Defines for selecting the correct Win32 API (i.e. many Win32 APIs required for use in Windows Store apps are the Vista (0x0600), Windows 7 (0x0601), or Windows 8 (0x0602) version.

You can use WINVER or _WIN32_WINNT.