Original
Raising and handling exceptions
To create
an exception object, call the exception class’s constructor within a raise
statement. For example,
raise
EMathError.Create;
In
general, the form of a raise statement is
raise object
at address
where object and at address
are both optional. If object is omitted, the statement re-raises the
current exception; see Re-raising
exceptions. When an address is specified, it is usually a pointer to
a procedure or function; use this option to raise the exception from an earlier
point in the stack than the one where the error actually occurred.
When an
exception is raised, that is, referenced in a raise statement it is
governed by special exception-handling logic. A raise statement never
returns control in the normal way. Instead, it transfers control to the
innermost exception handler that can handle exceptions of the given class. (The
innermost handler is the one whose try...except block was most recently
entered but has not yet exited.)
For example,
the function below converts a string to an integer, raising an ERangeError
exception if the resulting value is outside a specified range.
function
StrToIntRange(const S: string; Min, Max: Longint): Longint;
begin
Result := StrToInt(S); // StrToInt is declared in SysUtils
if (Result < Min) or
(Result > Max) then
raise
ERangeError.CreateFmt(
'%d is not
within the valid range of %d..%d',
[Result, Min,
Max]);
end;
Notice
the CreateFmt method called in the raise statement. Exception
and its descendants have special constructors that provide alternative ways to
create exception messages and context IDs.
A raised exception is destroyed automatically after it is handled. Never attempt to destroy a raised exception manually.
Note: Raising
an exception in the initialization section of a unit may not produce the
intended result. Normal exception support comes from the SysUtils unit,
which must be initialized before such support is available. If an exception
occurs during initialization, all initialized units including SysUtils
are finalized and the exception is re-raised. Then the exception is caught and
handled, usually by interrupting the program.
See also
Exception
译文
引发和处理异常
要创建一个异常对象，应在raise语句中调用异常类的构造器，如
raise
EMathError.Create;
一般情况下，raise具有如下形式
raise object at address
这里的object和at address都是可选的。如果object被省略，那么语句将再引发当前异常（见再引发异常）。当某个address被指定时，通常是一个指向过程或函数的指针；利用该选项可以从堆栈中较早的点（与错误实际发生的点比较）引发异常。
异常被引发，即异常在raise语句中被引用时，异常由特殊的异常处理逻辑来管理。通常，raise语句从不返回控制。取而代之的是，它把控制传递到最内层的异常处理程序，该处理程序能处理给定类的异常。（最内层的处理程序就是一个try...except块中尚未退出的最近入口。）
例如，下面的函数把一个串转换为整数，如果结果在指定范围之外则引发一个ERangeError异常。
function
StrToIntRange(const S: string; Min, Max: Longint): Longint;
begin
Result := StrToInt(S); // StrToInt函数在SysUtils单元中定义
if (Result < Min) or
(Result > Max) then
raise
ERangeError.CreateFmt(
'%d is not
within the valid range of %d..%d',
[Result, Min,
Max]);
end;
可以注意到，在raise语句中调用的是CreateFmt方法。Exception类及其后裔类拥有特殊的构造器，为创建异常消息和环境ID提供多于一种途径。
引发的异常在其处理后自动销毁，决不要试图人为销毁一个引发的异常。
注意： 单元的初始化节中引发异常不能达到预期的结果。一般的异常支持来自SysUtils单元，在异常支持可用之前该单元必需被初始化。如果一个异常在初始化过程中发生，那么包括SysUtils单元在内所有初始化过的单元，都会被结束（finalized）并且异常被再引发。这时异常被捕获和处理，通常通过中断程序。
相关主题
Exception（详细信息见联机帮助）