delphi数组:Delphi2005学习笔记3——数组参数的研究来源: 发布时间:星期四, 2009年2月12日 浏览:181次 评论:0
有如下代码: procedure Change(a:.gif' /> of Int32); procedure Change0(var a:.gif' /> of Int32); type Ta = .gif' />[0..10] of Int32; procedure Change2(a:Ta); procedure Change3(var a:Ta); var aa:Ta; bb:.gif' /> of Int32; implementation {$AUTOBOX _disibledevent=> a:=bb; end; procedure Change0(var a:.gif' /> 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; 然后执行下面语句 SetLength(bb,11);bb[0]:=5678; aa := Ta(&Array.CreateInstance(typeof(Int32),11)); aa[0]:=0; Change(aa); MessageBox.Show(aa[0].); &Object(aa)=&Object(bb) then MessageBox.Show(\'=\'); aa := Ta(&Array.CreateInstance(typeof(Int32),11)); aa[0]:=0; Change0(aa); MessageBox.Show(aa[0].); &Object(aa)=&Object(bb) then MessageBox.Show(\'=\'); aa := Ta(&Array.CreateInstance(typeof(Int32),11)); aa[0]:=0; Change2(aa); MessageBox.Show(aa[0].); &Object(aa)=&Object(bb) then MessageBox.Show(\'=\'); aa := Ta(&Array.CreateInstance(typeof(Int32),11)); aa[0]:=0; Change3(aa); MessageBox.Show(aa[0].); &Object(aa)=&Object(bb) then MessageBox.Show(\'=\'); 结果发现 .gif' /> of Int32 方式可以改变元素值但不能改变变量中存储首地址输出123 var .gif' /> of Int32 既可以改变值又可以改变变量中存储首地址输出5678和= Ta方式不能改变元素值但是却很奇怪aa和bb指向同个输出0和= var Ta方式 可以改变元素值但是却不是5678而是123;但是aa和bb指向同个输出123和= 反汇编结果如下 method public void Change(32 a) cil managed { // Code Size: 13 (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 32 WinForm.Units.WinForm::bb L_000a: starg.s a L_000c: ret } .method public void Change0(32& a) cil managed{ // Code Size: 14 (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 32 WinForm.Units.WinForm::bb L_000c: stind.ref L_000d: ret } .method public void Change2(32 a) cil managed{ // Code Size: 42 (s) .maxstack 4 .locals ( 32 num1) L_0000: ldarg.0 L_0001: callvirt instance object [mscorlib].Array::Clone L_0006: cast 32 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 32 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].Array::Copy([mscorlib].Array, [mscorlib].Array, 32) L_0029: ret } .method public void Change3(32& a) cil managed{ // Code Size: 31 (s) .maxstack 4 .locals ( 32 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 32 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].Array::Copy([mscorlib].Array, [mscorlib].Array, 32) L_001e: ret } 结论: 使用.gif' /> of Int32 方式实际上对应于C#可变数目参数即 params Int32 这种参数方式是传递首地址(即参数值)而不是存放首地址变量地址 加上Var修饰即加入ref修饰传递是存放首地址变量地址(即参数变量自身地址) 使用Ta方式则在内部对值进行克隆既不改变首地址也不改变原值 加入var 修饰好像传递是变量自身地址这里还是没看懂是为什么 对应C#代码为 public void Change(params a){ a[0] = 0x7b; a = WinForm.bb;} public void Change0(params ref a){ a[0] = 0x7b; a = WinForm.bb;} public void Change2( a){ a = () a.Clone; a[0] = 0x7b; num1 = WinForm.bb.Length; (num1 > 11) { num1 = 11; } Array.Copy(WinForm.bb, a, num1);} public void Change3(ref a){ a[0] = 0x7b; num1 = WinForm.bb.Length; (num1 > 11) { num1 = 11; } Array.Copy(WinForm.bb, a, num1);} 0
相关文章读者评论发表评论 |
|