在Delphi中哪些变量被初始化？ [英] Which variables are initialized when in Delphi?

问题描述

所以我总是听说类字段（基于堆）被初始化，但是基于堆栈的变量没有被初始化。我也听说记录成员（也是基于堆栈）也没有被初始化。编译器警告局部变量未初始化（[DCC警告] W1036变量'x'可能未初始化），但不会对记录成员发出警告。所以我决定进行测试。

So I always heard that class fields (heap based) were initialized, but stack based variables were not. I also heard that record members (also being stack based) were also not initialized. The compiler warns that local variables are not initialized ([DCC Warning] W1036 Variable 'x' might not have been initialized), but does not warn for record members. So I decided to run a test.

我总是从整数和 false 从 Booleans 为所有记录成员。

I always get 0 from Integers and false from Booleans for all record members.

我尝试转动各种编译器选项（调试，优化等）开启和关闭，但没有任何区别。我的所有记录成员正在初始化。

I tried turning various compiler options (debugging, optimizations, etc.) on and off, but there was no difference. All my record members are being initialized.

我缺少什么？我在德尔福2009年更新2。

What am I missing? I am on Delphi 2009 Update 2.

program TestInitialization;

{$APPTYPE CONSOLE}

uses
  SysUtils;

type
  TR = Record
  Public
    i1, i2, i3, i4, i5: Integer;
    a: array[0..10] of Integer;
    b1, b2, b3, b4, b5: Boolean;
    s: String;
  End;

var
  r: TR;
  x: Integer;

begin
  try
    WriteLn('Testing record. . . .');
    WriteLn('i1 ',R.i1);
    WriteLn('i2 ',R.i2);
    WriteLn('i3 ',R.i3);
    WriteLn('i4 ',R.i4);
    WriteLn('i5 ',R.i5);

    Writeln('S ',R.s);

    Writeln('Booleans: ', R.b1, ' ', R.b2, ' ', R.b3, ' ', R.b4, ' ', R.b5);

    Writeln('Array ');
    for x := 0 to 10 do
      Write(R.a[x], ' ');
    WriteLn;

    WriteLn('Done . . . .');
  except
    on E:Exception do
      Writeln(E.Classname, ': ', E.Message);
  end;
  ReadLn;
end.

输出：

Testing record. . . .
i1 0
i2 0
i3 0
i4 0
i5 0
S
Booleans: FALSE FALSE FALSE FALSE FALSE
Array
0 0 0 0 0 0 0 0 0 0 0
Done . . . .

推荐答案

全局变量为零初始化。在程序主程序的上下文中使用的变量可能是一个特殊情况;在程序的主要开始有时它们被视为局部变量，特别是 -loop indexers的。但是，在您的示例中， r 是一个全局变量，并从可执行文件的.bss部分分配，Windows加载器确保零填充。

Global variables are zero-initialized. Variables used in the context of the main begin..end block of a program can be a special case; sometimes they are treated as local variables, particularly for-loop indexers. However, in your example, r is a global variable and allocated from the .bss section of the executable, which the Windows loader ensures is zero-filled.

局部变量被初始化，就像将它们传递给 Initialize 例程一样。 Initialize 例程使用运行时类型信息（RTTI）来清零字段（递归地 - 如果字段是数组或记录类型）和数组（递归 - 如果元素类型是一个托管类型的数组或记录），托管类型是以下之一：

Local variables are initialized as if they were passed to the Initialize routine. The Initialize routine uses runtime type-info (RTTI) to zero-out fields (recursively - if a field is of an array or record type) and arrays (recursively - if the element type is an array or a record) of a managed type, where a managed type is one of:

• AnsiString


• UnicodeString


• WideString


• 界面类型（包括方法引用）


• 动态数组类型


• 变体

• AnsiString
• UnicodeString
• WideString
• an interface type (including method references)
• dynamic array type
• Variant

堆中的分配不一定要初始化;这取决于使用什么机制来分配内存。作为实例对象数据的一部分的分配由 TObject.InitInstance 填充。来自 AllocMem 的分配是零填充的，而 GetMem 分配不是零填充。初始化新的分配将被初始化为初始化。

Allocations from the heap are not necessarily initialized; it depends on what mechanism was used to allocate memory. Allocations as part of instance object data are zero-filled by TObject.InitInstance. Allocations from AllocMem are zero-filled, while GetMem allocations are not zero-filled. Allocations from New are initialized as if they were passed to Initialize.

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