Object Pascal Language Guide Writing dynamically loadable librariesTopic groups See alsoThe main source for a dynamically loadable library is identical to that of a program, except that it begins with the reserved word library (instead of program). Only routines that a library explicitly exports are available for importing by other libraries or programs. The following example shows a library with two exported functions, Min and Max.library MinMax; function Min(X, Y: Integer): Integer; stdcall;begin if X < Y then Min := X else Min := Y; end;function Max(X, Y: Integer): Integer; stdcall;begin if X > Y then Max := X else Max := Y; end;exports Min, Max;beginend.If you want your library to be available to applications written in other languages, it’s safest to specify stdcall in the declarations of exported functions. Other languages may not support Object Pascal’s default register calling convention. Libraries can be built from multiple units. In this case, the library source file is frequently reduced to a uses clause, an exports clause, and the initialization code. For example,library Editors; uses EdInit, EdInOut, EdFormat, EdPrint; exports InitEditors, DoneEditors name Done, InsertText name Insert, DeleteSelection name Delete, FormatSelection, PrintSelection name Print, ... SetErrorHandler;begin InitLibrary; end.You can put exports clauses in the interface or implementation section of a unit. Any library that includes such a unit in its uses clause automatically exports the routines listed the unit’s exports clauses—without the need for an exports clause of its own. The directive local, which s routines as unavailable for export, is platform-specific and has no effect in Windows programming. On Linux, the local directive provides a slight performance optimization for routines that are compiled into a library but are not exported. This directive can be specified for standalone procedures and functions, but not for methods. A routine declared with local—for example,function Contraband(I: Integer): Integer; local;—does not refresh the EBX register and hencecannot be exported from a library. cannot be declared in the interface section of a unit. cannot have its address taken or be assigned to a procedural-type variable. if it is a pure assembler routine, cannot be called from another unit unless the caller sets up EBX.The exports clause Library initialization code Global variables in a library Libraries and system variables Exceptions and runtime errors in libraries The shared-memory manager (Windows only)
Writing dynamically loadable librariesTopic groups See alsoThe main source for a dynamically loadable library is identical to that of a program, except that it begins with the reserved word library (instead of program).
Only routines that a library explicitly exports are available for importing by other libraries or programs. The following example shows a library with two exported functions, Min and Max.library MinMax;
function Min(X, Y: Integer): Integer; stdcall;begin
if X < Y then Min := X else Min := Y;
end;function Max(X, Y: Integer): Integer; stdcall;begin
if X > Y then Max := X else Max := Y;
end;exports Min,
Max;beginend.If you want your library to be available to applications written in other languages, it’s safest to specify stdcall in the declarations of exported functions. Other languages may not support Object Pascal’s default register calling convention.
Libraries can be built from multiple units. In this case, the library source file is frequently reduced to a uses clause, an exports clause, and the initialization code. For example,library Editors;
uses EdInit, EdInOut, EdFormat, EdPrint;
exports InitEditors,
DoneEditors name Done,
InsertText name Insert,
DeleteSelection name Delete,
FormatSelection,
PrintSelection name Print,
...
SetErrorHandler;begin InitLibrary;
end.You can put exports clauses in the interface or implementation section of a unit. Any library that includes such a unit in its uses clause automatically exports the routines listed the unit’s exports clauses—without the need for an exports clause of its own.
The directive local, which s routines as unavailable for export, is platform-specific and has no effect in Windows programming.
On Linux, the local directive provides a slight performance optimization for routines that are compiled into a library but are not exported. This directive can be specified for standalone procedures and functions, but not for methods. A routine declared with local—for example,function Contraband(I: Integer): Integer; local;—does not refresh the EBX register and hencecannot be exported from a library.
cannot be declared in the interface section of a unit.
cannot have its address taken or be assigned to a procedural-type variable.
if it is a pure assembler routine, cannot be called from another unit unless the caller sets up EBX.The exports clause
Library initialization code
Global variables in a library
Libraries and system variables
Exceptions and runtime errors in libraries
The shared-memory manager (Windows only)