QueryActCtxW function (winbase.h)

The QueryActCtxW function queries the activation context.

Syntax

BOOL QueryActCtxW(
  [in]            DWORD  dwFlags,
  [in]            HANDLE hActCtx,
  [in, optional]  PVOID  pvSubInstance,
  [in]            ULONG  ulInfoClass,
  [out]           PVOID  pvBuffer,
  [in, optional]  SIZE_T cbBuffer,
  [out, optional] SIZE_T *pcbWrittenOrRequired
);

Parameters

[in] dwFlags

This parameter should be set to one of the following flag bits.

[in] hActCtx

Handle to the activation context that is being queried.

[in, optional] pvSubInstance

Index of the assembly, or assembly and file combination, in the activation context. The meaning of the pvSubInstance depends on the option specified by the value of the ulInfoClass parameter.

This parameter may be null.

[in] ulInfoClass

This parameter can have only the values shown in the following table.

[out] pvBuffer

Pointer to a buffer that holds the returned information. This parameter is optional. If pvBuffer is null, then cbBuffer must be zero. If the size of the buffer pointed to by pvBuffer is too small, QueryActCtxW returns ERROR_INSUFFICIENT_BUFFER and no data is written into the buffer. See the Remarks section for the method you can use to determine the required size of the buffer.

[in, optional] cbBuffer

Size of the buffer in bytes pointed to by pvBuffer. This parameter is optional.

[out, optional] pcbWrittenOrRequired

Number of bytes written or required. The parameter pcbWrittenOrRequired can only be NULL when pvBuffer is NULL. If pcbWrittenOrRequired is non-NULL, it is filled with the number of bytes required to store the returned buffer.

Return value

If the function succeeds, it returns TRUE. Otherwise, it returns FALSE.

This function sets errors that can be retrieved by calling GetLastError. For an example, see Retrieving the Last-Error Code. For a complete list of error codes, see System Error Codes.

Remarks

The parameter cbBuffer specifies the size in bytes of the buffer pointed to by pvBuffer. If pvBuffer is NULL, then cbBuffer must be 0. The parameter pcbWrittenOrRequired can only be NULL if pvBuffer is NULL. If pcbWrittenOrRequired is non-NULL on return, it is filled with the number of bytes required to store the returned information. When the information data returned is larger than the provided buffer, QueryActCtxW returns ERROR_INSUFFICIENT_BUFFER and no data is written to the buffer pointed to by pvBuffer.

The following example shows the method of calling first with a small buffer and then recalling if the buffer is too small.

SIZE_T cbRequired;
PVOID pvData = NULL;
SIZE_T cbAvailable = 0;

if (!QueryActCtxW(..., pvData, cbAvailable, &cbRequired) && (GetLastError()== ERROR_INSUFFICIENT_BUFFER))
{
    // Allocate enough space to store the returned buffer, fail if too small
    if (NULL == (pvData = HeapAlloc(GetProcessHeap(), 0, cbRequired)))
    {
        SetLastError(ERROR_NOT_ENOUGH_MEMORY);
        return FALSE;
    }
    cbAvailable = cbRequired;
    // Try again, this should succeed.
    if (QueryActCtxW(..., pvData, cbAvailable, &cbRequired))
    {
        // Use the returned data in pvData
    }
    HeapFree(GetProcessHeap(), 0, pvData);
    pvData = NULL;
}

Requirements