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标题: 关于vc中函数堆栈变量的分配 [打印本页]

作者: 白色海岸线 时间: 2006-9-15 11:48 标题: 关于vc中函数堆栈变量的分配

一段代码,从中能看到些东西.关于数组,字符串,指针,编译器自动初始化,数据对齐.
0040B4E0 push       ebp
0040B4E1 mov       ebp,esp
0040B4E3 sub       esp,8Ch
0040B4E9 push       ebx
0040B4EA push       esi
0040B4EB push       edi
0040B4EC lea       edi,[ebp-8Ch]
0040B4F2 mov       ecx,23h
0040B4F7 mov       eax,0CCCCCCCCh
0040B4FC rep stos dword ptr [edi]
5:       int ret = 0;
0040B4FE mov       dword ptr [ebp-4],0
6:       char a ;    //这里没有给他初始化,编译器为其保留了8个字节的空间,应该是对齐的原因
7:       char b = ';b';;
0040B505 mov       byte ptr [ebp-0Ch],62h
8:       char c[2]; //同样没有初始化,一共是2个字节,但是对齐,保留了8字节
9:       char d[2] = {';\0';}; //编译器为第一个字节设值,后续的值全初始为0
0040B509 mov       byte ptr [ebp-14h],0
0040B50D xor       eax,eax
0040B50F mov       byte ptr [ebp-13h],al
10:    char e[3] = {';a';, ';b';, ';c';}; //初始化为立即值,由于对齐,也是4字节空间
0040B512 mov       byte ptr [ebp-18h],61h
0040B516 mov       byte ptr [ebp-17h],62h
0040B51A mov       byte ptr [ebp-16h],63h
11:    char f[4] = "aaa";          //初始化指向一段字符串,最后一值默认为0,逐个复制到栈中
0040B51E mov       ecx,dword ptr [string "aa" (0041f10c)]
0040B524 mov       dword ptr [ebp-1Ch],ecx
12:    char h[5] = "bbbb";       //同上,但是由于对齐,其大小为8字节
0040B527 mov       edx,dword ptr [string "bbbb" (0041ff44)]
0040B52D mov       dword ptr [ebp-24h],edx
0040B530 mov       al,[string "bbbb"+4 (0041ff48)]
0040B535 mov       byte ptr [ebp-20h],al
13:    char i[] = {';d';};          //数组大小为1字节,但是对齐使其为4字节
0040B538 mov       byte ptr [ebp-28h],64h
14:    char j[] = {';\0';};       //数组大小为1字节,对齐为4字节
0040B53C mov       byte ptr [ebp-2Ch],0
15:    char k[] = "ccccc";       //数组大小为6字节,因为编译器为字符串最后加0,对齐为8字节
0040B540 mov       ecx,dword ptr [string "ccccc" (0041ff3c)]//逐个拷贝到栈
0040B546 mov       dword ptr [ebp-34h],ecx
0040B549 mov       dx,word ptr [string "ccccc"+4 (0041ff40)]
0040B550 mov       word ptr [ebp-30h],dx
16:    char l[] = {';a';, ';b';, ';c';, ';d';, ';e';, ';f';};//数组长度为6,注意这里为立即数而非字符串
0040B554 mov       byte ptr [ebp-3Ch],61h //对齐为8字节
0040B558 mov       byte ptr [ebp-3Bh],62h
0040B55C mov       byte ptr [ebp-3Ah],63h
0040B560 mov       byte ptr [ebp-39h],64h
0040B564 mov       byte ptr [ebp-38h],65h
0040B568 mov       byte ptr [ebp-37h],66h
17:    char m[6];                //树组长度为6,未初始化,编译器为其保留8字节
18:    char n[7] = {';\0';};       //数组长度为7,第一个值赋值为0,其后编译器自动初始化为0
0040B56C mov       byte ptr [ebp-4Ch],0 //对齐为8字节
0040B570 xor       eax,eax
0040B572 mov       dword ptr [ebp-4Bh],eax
0040B575 mov       word ptr [ebp-47h],ax
19:
20:
21:
22:
23:    return ret;
0040B579 mov       eax,dword ptr [ebp-4]
24: }
0040B57C pop       edi
0040B57D pop       esi
0040B57E pop       ebx
0040B57F mov       esp,ebp
0040B581 pop       ebp
0040B582 ret

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