MSDN Library

SAFEARRAY Data Type [Automation]

The definition for a safe array varies, depending on the target operating system platform. On 32-bit Windows systems, both the cbElements and cLocks parameters are unsigned long integers, and the handle parameter is omitted. On 16-bit Windows systems, cbElements and cLocks are unsigned short integers. The handle parameter is retained for compatibility with earlier software. For example:

typedef struct FARSTRUCT tagSAFEARRAY {
   unsigned short cDims;       // Count of dimensions in this array.
   unsigned short fFeatures;   // Flags used by the SafeArray
                        // routines documented below.
#if defined(WIN32)
   unsigned long cbElements;   // Size of an element of the array.
                        // Does not include size of
                        // pointed-to data.
   unsigned long cLocks;      // Number of times the array has been 
                        // locked without corresponding unlock.
   unsigned short cbElements;
   unsigned short cLocks;
   unsigned long handle;      // Used on Macintosh only.
   void HUGEP* pvData;             // Pointer to the data.
   SAFEARRAYBOUND rgsabound[1];      // One bound for each dimension.

All public static members of the SAFEARRAY data type are thread safe. Instance members are not guaranteed to be thread safe.

For example, consider an application that uses the SafeArrayLock Function and SafeArrayUnlock Function functions. If these functions are called concurrently from different threads on the same SAFEARRAY data type instance, an inconsistent lock count may be created. This will eventually cause the SafeArrayUnlock Function function to return E_UNEXPECTED. You can prevent this by providing your own synchronization code.

The array rgsabound is stored with the left-most dimension in rgsabound[0] and the right-most dimension in rgsabound[cDims - 1]. If an array was specified in a C-like syntax as a [2][5], it would have two elements in the rgsabound vector. Element 0 has an lLbound of 0 and a cElements of 2. Element 1 has an lLbound of 0 and a cElements of 5.

The fFeatures flags describe attributes of an array that can affect how the array is released. The fFeatures field describes what type of data is stored in the SAFEARRAY and how the array is allocated. This allows freeing the array without referencing its containing variant. The bits are accessed using the following constants:

fFeatures Flags


FADF_AUTO 0x0001

An array that is allocated on the stack.


An array that is statically allocated.


An array that is embedded in a structure.


An array that may not be resized or reallocated.


An array that contains records. When set, there will be a pointer to the IRecordinfo interface at negative offset 4 in the array descriptor.


An array that has an IID identifying interface. When set, there will be a GUID at negative offset 16 in the safe array descriptor. Flag is set only when FADF_DISPATCH or FADF_UNKNOWN is also set.


An array that has a VT type. When set, there will be a VT tag at negative offset 4 in the array descriptor that specifies the element type.

FADF_BSTR 0x0100

An array of BSTRs.


An array of IUnknown*.


An array of IDispatch*.


An array of VARIANTs.


Bits reserved for future use.

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