Class TDynLib
Unit
CastleDynLib
Declaration
type TDynLib = class(TObject)
Description
Load functions from dynamic libraries.
I wrote my own class to handle dynamic libraries because:
I wanted to have Load and Symbol functions that by default do error checking (and raise necessary exceptions).
I wanted to have a field SymbolErrorBehaviour — this lets me to specify, once for all subsequent Symbol calls, what error checking I want. Default is to check errors and raise exceptions. There is also a very usefull value reWarnAndContinue: it allows you to run program once and see all symbols that are missing from dynamic library.
Also, the interface of this is OS-independent and works for both FPC and Delphi, so you can avoid ugly $ifdefs in your code.
Typical usage:
var
ALLibrary: TDynLib = nil;
initialization
ALLibrary := TDynLib.Load('libopenal.so');
finalization
FreeAndNil(ALLibrary);
end.
It is important that ALLibrary is initialized to nil (actually, writing " = nil" is not necessary for a global variable) and that in finalization you use Free(AndNil). This allows you to exit gracefully if library does not exist on the system and Load will raise an exception: ALLibrary will stay then as nil and FreeAndNil(ALLibrary) will be a valid NOP. Using FreeAndNil(ALLibrary) instead of ALLibrary.Free is just a good practice.
Hierarchy
Overview
Methods
 |
constructor Create(const AName: string; AHandle: TDynLibHandle); |
 |
destructor Destroy; override; |
 |
class function Load(const AName: string; RaiseExceptionOnError: boolean = true): TDynLib; |
 |
function Symbol(SymbolName: PChar): Pointer; |
Properties
Description
Methods
 |
constructor Create(const AName: string; AHandle: TDynLibHandle); |
Standard constructor, requires a valid TDynLibHandle already. Usually you will prefer to use Load method instead of directly calling this constructor.
Exceptions raised
- ECheckFailed
- if you supply invalid handle.
|
 |
destructor Destroy; override; |
|
 |
class function Load(const AName: string; RaiseExceptionOnError: boolean = true): TDynLib; |
Link to a dynamic library specified by Name. Returns created TDynLib instance.
If the library is not found and RaiseExceptionOnError is False , Nil will be returned. If RaiseExceptionOnError is True then EDynLibError will be raised in case library is not found. So if RaiseExceptionOnError is True , Nil is never returned.
Note that the default situation prevents from unintentionally ignoring an error and that's good.
Exceptions raised
- EDynLibError
- If library not found and RaiseExceptionOnError is
True .
|
 |
function Symbol(SymbolName: PChar): Pointer; |
Return address of given symbol (function name etc.) from loaded dynamic library. If the symbol doesn't exist, then SymbolErrorBehaviour says what happens:
seRaise (default), then EDynLibError will be raised.
seReturnNil, then return Nil (and continue, ignoring error).
seWarnAndReturnNil, then write warning (using WarningWrite) and return Nil (and continue, ignoring error).
This is useful for debugging : you can easily open the library and after one run of the program you can see what symbols (that you requested) were missing from the library. This is useful when you have a library but you are not sure whether it is compatible and contains all the symbols that you want.
Exceptions raised
- EDynLibError
- If SymbolName doesn't exist and SymbolErrorBehaviour is seRaise.
|
Properties
 |
property Name: string read FName; |
Name of the library to link to. In practice, file name of the *.so or *.dylib or *.dll file.
A precise strategy where this library is searched is specific to a platform, see the semantics of SysUtils.LoadLibrary (DynLibs for FPC) call on given OS.
|
Generated by PasDoc 0.15.0.
|