AFGetProperty(3) AFGetProperty(3) NAME AFGetProperty, AFListProperties, AFChangeProperty, AFDeleteProperty - obtain and change properties SYNTAX #include <AF/AFlib.h> int AFGetProperty(AC ac, AAtom property, long long_offset, long long_length, ABool delete, AAtom req_type, AAtom *actual_type_return, int *actual_format_return, unsigned long *nitems_return, unsigned long *bytes_after_return, unsigned char **prop_return) AAtom *AFListProperties(AC ac, int *num_prop_return) AFChangeProperty(AC ac, AAtom property, AAtom type, int format, int mode, unsigned char *data, int nelements) AFDeleteProperty(AC ac, AAtom property) ARGUMENTS actual_format_return Returns the actual format of the property. actual_type_return Returns the atom identifier that defines the actual type of the property. bytes_after_return Returns the number of bytes remaining to be read in the property if a partial read was performed. data Specifies the property data. delete Specifies a Boolean value that determines whether the property is deleted. ac Specifies the device to use (via an audio context). format Specifies whether the data should be viewed as a list of 8-bit, 16-bit, or 32-bit quantities. Possible values are 8, 16, and 32. This information allows the AF server to correctly perform byte- swap operations as necessary. If the format is 16-bit or 32-bit, you must explicitly cast your data pointer to an (unsigned char *) in the call to AFChangeProperty. long_length Specifies the length in 32-bit multiples of the data to be retrieved. long_offset Specifies the offset in the specified property (in 32-bit quantities) where the data is to be retrieved. mode Specifies the mode of the operation. You can pass APropModeRe- place, APropModePrepend, or APropModeAppend. nelements Specifies the number of elements of the specified data format. nitems_return Returns the actual number of 8-bit, 16-bit, or 32-bit items stored in the prop_return data. num_prop Specifies the length of the properties array. num_prop_return Returns the length of the properties array. npositions Specifies the rotation amount. prop_return Returns the data in the specified format. property Specifies the property name. properties Specifies the array of properties that are to be rotated. req_type Specifies the atom identifier associated with the property type or AAnyPropertyType. type Specifies the type of the property. The AF server does not interpret the type but simply passes it back to an application that later calls AFGetProperty. DESCRIPTION The AFGetProperty function returns the actual type of the property; the actual format of the property; the number of 8-bit, 16-bit, or 32-bit items transferred; the number of bytes remaining to be read in the property; and a pointer to the data actually returned. AFGetProperty sets the return arguments as follows: o If the specified property does not exist for the specified device, AFGetProperty returns None to actual_type_return and the value zero to actual_format_return and bytes_after_return. The nitems_return argu- ment is empty. In this case, the delete argument is ignored. o If the specified property exists but its type does not match the specified type, AFGetProperty returns the actual property type to actual_type_return, the actual property format (never zero) to actual_format_return, and the property length in bytes (even if the actual_format_return is 16 or 32) to bytes_after_return. It also ignores the delete argument. The nitems_return argument is empty. o If the specified property exists and either you assign AAnyProper- tyType to the req_type argument or the specified type matches the actual property type, AFGetProperty returns the actual property type to actual_type_return and the actual property format (never zero) to actual_format_return. It also returns a value to bytes_after_return and nitems_return, by defining the following values: N = actual length of the stored property in bytes (even if the format is 16 or 32) I = 4 * long_offset T = N - I L = MINIMUM(T, 4 * long_length) A = N - (I + L) The returned value starts at byte index I in the property (indexing from zero), and its length in bytes is L. If the value for long_offset causes L to be negative, a BadValue error results. The value of bytes_after_return is A, giving the number of trailing unread bytes in the stored property. AFGetProperty always allocates one extra byte in prop_return (even if the property is zero length) and sets it to ASCII null so that simple proper- ties consisting of characters do not have to be copied into yet another string before use. If delete is True and bytes_after_return is zero, AFGetProperty deletes the property from the device and generates a Proper- tyNotify event on the device. The function returns Success if it executes successfully. To free the resulting data, use Afree. AFGetProperty can generate BadAtom, BadValue, and BadAC errors. The AFListProperties function returns a pointer to an array of atom proper- ties that are defined for the specified device or returns NULL if no pro- perties were found. To free the memory allocated by this function, use Afree. AFListProperties can generate a BadAC error. The AFChangeProperty function alters the property for the specified device and causes the AudioFIle server to generate a PropertyNotify event on that device. AFChangeProperty performs the following: o If mode is APropModeReplace, AFChangeProperty discards the previous property value and stores the new data. o If mode is APropModePrepend or APropModeAppend, AFChangeProperty inserts the specified data before the beginning of the existing data or onto the end of the existing data, respectively. The type and for- mat must match the existing property value, or a BadMatch error results. If the property is undefined, it is treated as defined with the correct type and format with zero-length data. The lifetime of a property is not tied to the storing client. Properties remain until explicitly deleted, or until the server resets. The maximum size of a property is server dependent and can vary dynamically depending on the amount of memory the server has available. (If there is insuffi- cient space, a ABadAlloc error results.) AFChangeProperty can generate ABadAlloc, ABadAtom, ABadMatch, ABadValue, and ABadAC errors. The AFDeleteProperty function deletes the specified property only if the property was defined on the specified device and causes the AF server to generate a PropertyNotify event on the device unless the property does not exist. AFDeleteProperty can generate ABadAtom and ABadAC errors. DIAGNOSTICS ABadAlloc The server failed to allocate the requested resource or server memory. ABadAtom A value for an Atom argument does not name a defined Atom. ABadValue Some numeric value falls outside the range of values accepted by the request. Unless a specific range is specified for an argument, the full range defined by the argument's type is accepted. Any argument defined as a set of alternatives can gen- erate this error. ABadAC A value for a audio context argument is not valid. SEE ALSO AF(1) BUGS If you encounter a reproducible bug, please submit a problem report to (af-bugs@crl.dec.com). COPYRIGHT Copyright 1990-1994, Digital Equipment Corporation. See AF(1) for a full statement of rights and permissions. AUTHORS Digital Cambridge Research Lab