Function

AEGetParamPtr

Gets a copy of the data for a specified Apple event parameter from an Apple event or an Apple event record.

Declaration

OSErr AEGetParamPtr(const AppleEvent *theAppleEvent, AEKeyword theAEKeyword, DescType desiredType, DescType *actualType, void *dataPtr, Size maximumSize, Size *actualSize);

Parameters

theAppleEvent: A pointer to the Apple event to get the parameter data from.
theAEKeyword: The keyword that specifies the desired Apple event parameter. Some keyword constants are described in Keyword Parameter Constants.
desiredType: The desired descriptor type for the copied data. For a list of AppleScript’s predefined descriptor types, see Descriptor Type Constants.
If the descriptor specified by the theAEKeyword parameter is not of the desired type, AEGetParamPtr attempts to coerce the data to this type. However, if the desired type is typeWildCard, no coercion is performed.
On return, you can determine the actual descriptor type by examining the typeCode parameter.
typeCode: A pointer to a descriptor type. On return, specifies the descriptor type of the data pointed to by dataPtr. The returned type is either the same as the type specified by the desiredType parameter or, if the desired type was type wildcard, the true type of the descriptor. Specify NULL if you do not care about this return value. For a list of AppleScript’s predefined descriptor types, see Descriptor Type Constants.
dataPtr: A pointer to a buffer, local variable, or other storage location created and disposed of by your application. The size in bytes must be at least as large as the value you pass in the maximumSize parameter. On return, contains the parameter data. Specify NULL if you do not care about this return value.
maximumSize: The maximum length, in bytes, of the expected Apple event parameter data. The AEGetParamPtr function will not return more data than you specify in this parameter.
actualSize: A pointer to a variable of type Size. On return, the length, in bytes, of the data for the specified Apple event parameter. If this value is larger than the value you passed in the maximumSize parameter, the buffer pointed to by dataPtr was not large enough to contain all of the data for the parameter, though AEGetParamPtr does not write beyond the end of the buffer. If the buffer was too small, you can resize it and call AEGetParamPtr again. Specify NULL if you do not care about this return value.

Return Value

A result code. See Result Codes.

Discussion

You should use this function only to extract data from value descriptors such as typeUTF8Text.

Because this function allows you to specify a desired type, it can result in coercion. When used correctly, this has the positive effect of returning the data in the desired format. However, it can have side effects you may not be expecting, such as the overhead of calls to coercion handlers. See also the Version Notes section below for possible problems with coercion.

To get Apple event parameter data for your application to use directly, call AEGetParamPtr. To get a descriptor for an Apple event parameter to pass on to another Apple Event Manager routine, call AEGetParamDesc.

Before calling AEGetParamPtr, you can call the AESizeOfParam function to determine a size for the dataPtr buffer. However, unless you specify typeWildCard for the desiredType parameter, AEGetParamPtr may coerce the data, which may cause the size of the data to change.

In some cases, you may get improved efficiency extracting information from an Apple event with the AEGetDescDataRange function.

Version-Notes

Thread safe starting in OS X v10.2.

If the actual parameter you are getting with AEGetParamPtr is a record, AEGetParamPtr will erroneously allow you to get the parameter as any type at all, when it really should allow only typeAERecord, typeAEList, or typeWildcard. For other types, it will place raw record data into the designated buffer. With AppleScript 1.1.2, it would then return errAECoercionFail, as expected. With AppleScript 1.3 and later, however, it returns noErr.

You can work around this problem by checking the returned parameter from any call to AEGetParamPtr. If the source type is typeAERecord and the type you asked for was anything other than typeAERecord, typeAEList, or typeWildcard, you should assume the coercion failed.