C#中struct与class
请问结构类型new 与不new 在内存中有什么区别吗？值类型是在栈里面分配空间，结构是值类型如果new了后还是在栈里面分配空间吗？
下面是两份代码，第一份结构类型没有new直接给它里面的引用类型传引用。第二份是结构类型new了后在给它里面的引用类型传引用。从IL代码中我们可以看到是有区别的，因为对IL还不太熟悉，不知道它们内存怎么分配的，而且也不知道是在什么时候分配的，所以望高人指点。
using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
namespace StructAndClass
{
class Program
{
static void Main(string[] args)
{
ClassText classText;
classText = new ClassText();
classText.num = 5;
classText.name = "Hello";
StructText structText;
structText.classText = classText;
}
}
public class ClassText
{
public int num;
public string name;
}
public struct StructText
{
public ClassText classText;
public int n;
}
}
Main函数的IL代码
.method private hidebysig static void Main(string[] args) cil managed
{
.entrypoint
// 代码大小 34 (0x22)
.maxstack 2
.locals init (class StructAndClass.ClassText V_0,
valuetype StructAndClass.StructText V_1)
IL_0000: nop
IL_0001: newobj instance void StructAndClass.ClassText::.ctor()
IL_0006: stloc.0
IL_0007: ldloc.0
IL_0008: ldc.i4.5
IL_0009: stfld int32 StructAndClass.ClassText::num
IL_000e: ldloc.0
IL_000f: ldstr "Hello"
IL_0014: stfld string StructAndClass.ClassText::name
IL_0019: ldloca.s V_1
IL_001b: ldloc.0
IL_001c: stfld class StructAndClass.ClassText StructAndClass.StructText::classText
IL_0021: ret
} // end of method Program::Main
第二份代码
using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
namespace StructAndClass
{
class Program
{
static void Main(string[] args)
{
ClassText classText;
classText = new ClassText();
classText.num = 5;
classText.name = "Hello";
StructText structText = new StructText();
structText.classText = classText;
int x = structText.n;
}
}
public class ClassText
{
public int num;
public string name;
}
public struct StructText
{
public ClassText classText;
public int n;
}
}
Main函数的IL代码
.method private hidebysig static void Main(string[] args) cil managed
{
.entrypoint
// 代码大小 42 (0x2a)
.maxstack 2
.locals init (class StructAndClass.ClassText V_0,
valuetype StructAndClass.StructText V_1)
IL_0000: nop
IL_0001: newobj instance void StructAndClass.ClassText::.ctor()
IL_0006: stloc.0
IL_0007: ldloc.0
IL_0008: ldc.i4.5
IL_0009: stfld int32 StructAndClass.ClassText::num
IL_000e: ldloc.0
IL_000f: ldstr "Hello"
IL_0014: stfld string StructAndClass.ClassText::name
IL_0019: ldloca.s V_1
IL_001b: initobj StructAndClass.StructText
IL_0021: ldloca.s V_1
IL_0023: ldloc.0
IL_0024: stfld class StructAndClass.ClassText StructAndClass.StructText::classText
IL_0029: ret
} // end of method Program::Main
第二份IL代码明显多了两行，既然是初始化但也要给它分配空间呀，那是什么时候分的呢？
[解决办法]
调试的时候,看的汇编编码
- Assembly code
static void func() {00000000 push ebp 00000001 mov ebp,esp//保存了esp到ebp中 00000003 push edi 00000004 push esi 00000005 push ebx 00000006 sub esp,3Ch //分配局部变量内存00000009 xor eax,eax 0000000b mov dword ptr [ebp-44h],eax 0000000e mov dword ptr [ebp-40h],eax 00000011 mov dword ptr [ebp-10h],eax 00000014 xor eax,eax 00000016 mov dword ptr [ebp-1Ch],eax 00000019 cmp dword ptr ds:[00A89200h],0 00000020 je 00000027 00000022 call 76D66D87 00000027 xor ebx,ebx 00000029 xor edx,edx 0000002b mov dword ptr [ebp-48h],edx 0000002e nop ClassText classText; classText = new ClassText();0000002f mov ecx,0A89E94h 00000034 call FD6B0A5C 00000039 mov esi,eax 0000003b mov ecx,esi 0000003d call FD6CB0E0 00000042 mov ebx,esi classText.num = 5;00000044 mov dword ptr [ebx+8],5 classText.name = "Hello";0000004b mov eax,dword ptr ds:[023C3098h] 00000051 lea edx,[ebx+4] 00000054 call 76AB3F70 StructText structText = new StructText();00000059 lea edi,[ebp-44h] 0000005c pxor xmm0,xmm0 00000060 movq mmword ptr [edi],xmm0 structText.classText = classText;00000064 mov dword ptr [ebp-44h],ebx int x = structText.n;00000067 mov eax,dword ptr [ebp-40h] 0000006a mov dword ptr [ebp-48h],eax }0000006d nop 0000006e lea esp,[ebp-0Ch]//恢复esp 00000071 pop ebx 00000072 pop esi 00000073 pop edi 00000074 pop ebp 00000075 ret