Delphi2005学习笔记3——数组参数的研究

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有如下代码:
  procedure Change(a:array of Int32);
  procedure Change0(var a:array of Int32);
type
  Ta = array[0..10] of Int32;
  procedure Change2(a:Ta);
  procedure Change3(var a:Ta);

var
  aa:Ta;
  bb:array of Int32;

implementation

{$AUTOBOX ON}

procedure Change(a:array of Int32);
begin
  a[0]:=123;
  a:=bb;
end;

procedure Change0(var a:array of Int32);
begin
  a[0]:=123;
  a:=bb;
end;

procedure Change2(a:Ta);
begin
  a[0]:=123;
  a:=bb;
end;

procedure Change3(var a:Ta);
begin
  a[0]:=123;
  a:=bb;
end;

然后执行下面的语句
SetLength(bb,11);bb[0]:=5678;

  aa := Ta(&Array.CreateInstance(typeof(Int32),11));
  aa[0]:=0;
  Change(aa);
  MessageBox.Show(aa[0].ToString());
  if &Object(aa)=&Object(bb) then MessageBox.Show('=');

  aa := Ta(&Array.CreateInstance(typeof(Int32),11));
  aa[0]:=0;
  Change0(aa);
  MessageBox.Show(aa[0].ToString());
  if &Object(aa)=&Object(bb) then MessageBox.Show('=');

  aa := Ta(&Array.CreateInstance(typeof(Int32),11));
  aa[0]:=0;
  Change2(aa);
  MessageBox.Show(aa[0].ToString());
  if &Object(aa)=&Object(bb) then MessageBox.Show('=');

  aa := Ta(&Array.CreateInstance(typeof(Int32),11));
  aa[0]:=0;
  Change3(aa);
  MessageBox.Show(aa[0].ToString());
  if &Object(aa)=&Object(bb) then MessageBox.Show('=');
结果发现 array of Int32 方式,可以改变数组元素的值,但不能改变数组变量中存储的数组首地址,输出123
var  array of Int32 既可以改变数组的值,又可以改变数组变量中存储的数组首地址,输出5678和=
Ta方式,不能改变数组元素的值,但是却很奇怪,aa和bb指向同一个数组,输出0和=
var Ta方式 可以改变数组元素的值,但是却不是5678而是123;但是aa和bb指向同一个数组,输出123和=


反汇编结果如下
method public static void Change(int32[] a) cil managed
{
      // Code Size: 13 byte(s)
      .maxstack 3
      L_0000: ldarg.0
      L_0001: ldc.i4.0
      L_0002: ldc.i4.s 123
      L_0004: stelem.i4
      L_0005: ldsfld int32[] WinForm.Units.WinForm::bb
      L_000a: starg.s a
      L_000c: ret
}

.method public static void Change0(int32[]& a) cil managed { // Code Size: 14 byte(s) .maxstack 3 L_0000: ldarg.0 L_0001: ldind.ref L_0002: ldc.i4.0 L_0003: ldc.i4.s 123 L_0005: stelem.i4 L_0006: ldarg.0 L_0007: ldsfld int32[] WinForm.Units.WinForm::bb L_000c: stind.ref L_000d: ret }

.method public static void Change2(int32[] a) cil managed { // Code Size: 42 byte(s) .maxstack 4 .locals ( int32 num1) L_0000: ldarg.0 L_0001: callvirt instance object [mscorlib]System.Array::Clone() L_0006: castclass int32[] L_000b: starg.s a L_000d: ldarg.0 L_000e: ldc.i4.0 L_000f: ldc.i4.s 123 L_0011: stelem.i4 L_0012: ldsfld int32[] WinForm.Units.WinForm::bb L_0017: dup L_0018: ldlen L_0019: stloc.0 L_001a: ldarg.0 L_001b: ldloc.0 L_001c: ldc.i4.s 11 L_001e: ble.s L_0023 L_0020: ldc.i4.s 11 L_0022: stloc.0 L_0023: ldloc.0 L_0024: call void [mscorlib]System.Array::Copy([mscorlib]System.Array, [mscorlib]System.Array, int32) L_0029: ret }


.method public static void Change3(int32[]& a) cil managed { // Code Size: 31 byte(s) .maxstack 4 .locals ( int32 num1) L_0000: ldarg.0 L_0001: ldind.ref L_0002: ldc.i4.0 L_0003: ldc.i4.s 123 L_0005: stelem.i4 L_0006: ldsfld int32[] WinForm.Units.WinForm::bb L_000b: dup L_000c: ldlen L_000d: stloc.0 L_000e: ldarg.0 L_000f: ldind.ref L_0010: ldloc.0 L_0011: ldc.i4.s 11 L_0013: ble.s L_0018 L_0015: ldc.i4.s 11 L_0017: stloc.0 L_0018: ldloc.0 L_0019: call void [mscorlib]System.Array::Copy([mscorlib]System.Array, [mscorlib]System.Array, int32) L_001e: ret }
结论:
使用array of Int32 方式,实际上对应于C#的可变数目参数,即 params Int32[],
这种参数方式是传递的数组的首地址(即参数的值),而不是存放数组首地址的变量的地址
加上Var修饰,即加入ref修饰,传递的是存放数组首地址的变量的地址(即参数变量自身的地址)







使用Ta方式,则在函数内部对数组的值进行克隆,既不改变数组的首地址,也不改变原数组的值
加入var 修饰,好像传递的是变量自身的地址,这里还是没看懂是为什么。





对应的C#代码为

public static void Change(params int[] a) { a[0] = 0x7b; a = WinForm.bb; }

public static void Change0(params ref int[] a) { a[0] = 0x7b; a = WinForm.bb; }

public static void Change2(int[] a) { a = (int[]) a.Clone(); a[0] = 0x7b; int num1 = WinForm.bb.Length; if (num1 > 11) { num1 = 11; } Array.Copy(WinForm.bb, a, num1); }

public static void Change3(ref int[] a) { a[0] = 0x7b; int num1 = WinForm.bb.Length; if (num1 > 11) { num1 = 11; } Array.Copy(WinForm.bb, a, num1); }







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