Original
Writing dynamically loadable libraries
The 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;
begin
end.
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 marks 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 hence
· cannot 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.
Libraries and system variables
Exceptions and
runtime errors in libraries
The shared-memory manager (Windows only)
See also
Calling dynamically
loadable libraries
Libraries and packages: Overview
Program structure and syntax: Overview
译文
编写动态可加载库
动态可加载库的主源代码与程序的主源代码是一样的，除了前者以保留字library开始而后者以保留字program开始之外。
只有在库中被明确输出的例程可以被其他库或程序引入。下面是一个库的例子，该库有两个输出的函数，Min和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;
begin
end.
如果想要让库对由其他语言编写的由于程序是可用的，那么在输出函数的声明中指定stdcall调用约定是最可靠的。其他语言可能不支持Object
Pascal中缺省的register调用约定。
库可以由多个单元建立。此时，库的源文件通常缩减为一个uses子句，一个exports子句，以及初始化代码。例如，
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.
exports子句可以位于单元的接口节（interface）或实现节（implementation）。对于任何库，只要在其uses子句中包含了这样的单元，那么库会自动输出列于这些单元内exports子句中的所有例程，而不需要在库的exports子句中再次输出。
指示字local用于标明例程是不可被输出的，该指示字因具体平台的不同而具有不同的意义，它对Windows编程中没有影响。
在Linux中，local指示字对编译到库中但不被输出的例程提供一些性能优化。该指示字可以被指定到单独的过程和函数，但不能指定到方法。下面是用指示字local声明例程的例子，
function
Contraband(I: Integer): Integer; local;
由于该例程不能更新EBX寄存器，因此
· 不能从库中被输出。
· 不能声明在单元的接口节（interface）。
· 不能拥有自身的地址处理或被赋值到程序型变量。
· 如果例程是一个纯粹的汇编例程，那么它不能被其他单元调用，除非调用者设置了EBX寄存器。