while和for的效率c语⾔,【C语⾔】while与for执⾏效率对⽐【C语⾔】while与for执⾏效率对⽐
C语⾔编译环境: Microsoft Visual C++ 6.0(SP6)
测试程序
#include "stdio.h"
void forTest()
{
int num = 1234;// 迭代次数
for(int i=0;i
{
sum = sum + i;// 计算结果
}
printf("forTest:%d\n",sum);
}
void whileTest()
{
int num = 1234;// 迭代次数
long sum = 0;// 保存加法结果
while((num--)>0)
{
sum = sum + num;// 计算结果
}
printf("whileTest:%d\n",sum);
}
void main()
{
forTest();
whileTest();
}
汇编⽚段
--- D:\VC\ForWhile\ForWhile.cpp ------------------------------------------------------------------------------------------
17: void whileTest()
18: {
0040D760 push ebp
0040D761 mov ebp,esp
0040D763 sub esp,48h
0040D766 push ebx
0040D767 push esi
0040D768 push edi
0040D769 lea edi,[ebp-48h]
0040D76C mov ecx,12h
0040D771 mov eax,0CCCCCCCCh
0040D776 rep stos dword ptr [edi]
19: int num = 1234;
0040D778 mov dword ptr [ebp-4],4D2h 20: long sum = 0;
0040D77F mov dword ptr [ebp-8],0
21:
22: while((num--)>0)
0040D786 mov eax,dword ptr [ebp-4]
0040D789 mov ecx,dword ptr [ebp-4]
0040D78C sub ecx,1
0040D78F mov dword ptr [ebp-4],ecxlm5117
0040D792 test eax,eax
0040D794 jle whileTest+41h (0040d7a1) 23: {
24: sum = sum + num;
0040D796 mov edx,dword ptr [ebp-8]
0040D799 add edx,dword ptr [ebp-4]
0040D79C mov dword ptr [ebp-8],edx
25: }
0040D79F jmp whileTest+26h (0040d786) 26:
27: printf("whileTest:%d\n",sum);
0040D7A1 mov eax,dword ptr [ebp-8]
0040D7A4 push eax
0040D7A5 push offset string "whileTest:%d\n" (00422fac)
0040D7AA call printf (0040d6e0)
0040D7AF add esp,8
28: }
0040D7B2 pop edi
0040D7B3 pop esi
0040D7B4 pop ebx
0040D7B5 add esp,48h
0040D7B8 cmp ebp,esp
0040D7BA call __chkesp (0040d6a0)
0040D7BF mov esp,ebp
0040D7C1 pop ebp
0040D7C2 ret
-
-- No source file -------------------------------------------------------------------------------------------------------
分析:
0040D760~0040D776: 保存栈现场总共10条指令 0040D778: 迭代次数总共1条指令
0040D77F: 保存加法结果总共1条指令
0040D786~0040D79F: while循环总共10条指令 0040D7A1~0040D7AF: 打印结果总共5条指令
0040D7B2~0040D7C2: 恢复栈现场总共9条指令
合计: 36条指令
forTest()函数汇编后的指令:
--- D:\VC\ForWhile\ForWhile.cpp ------------------------------------------------------------------------------------------4: void forTest()
5: {
0040D3F0 push ebp
0040D3F1 mov ebp,esp
0040D3F3 sub esp,4Ch
0040D3F6 push ebx
0040D3F7 push esi
0040D3F8 push edi
0040D3F9 lea edi,[ebp-4Ch]
0040D3FC mov ecx,13h
0040D401 mov eax,0CCCCCCCCh
0040D406 rep stos dword ptr [edi]
6: int num = 1234;
0040D408 mov dword ptr [ebp-4],4D2h
7: long sum = 0;
0040D40F mov dword ptr [ebp-8],0
8:
9: for(int i=0;i
0040D416 mov dword ptr [ebp-0Ch],0
隔热断桥铝型材
0040D41D jmp forTest+38h (0040d428)
0040D41F mov eax,dword ptr [ebp-0Ch]
0040D422 add eax,1
0040D425 mov dword ptr [ebp-0Ch],eax
0040D428 mov ecx,dword ptr [ebp-0Ch]
0040D42B cmp ecx,dword ptr [ebp-4]
0040D42E jge forTest+4Bh (0040d43b)
10: {
11: sum = sum + i;
0040D430 mov edx,dword ptr [ebp-8]
0040D433 add edx,dword ptr [ebp-0Ch]
0040D436 mov dword ptr [ebp-8],edx
12: }
0040D439 jmp forTest+2Fh (0040d41f)
13:
14: printf("forTest:%d\n",sum);
0040D43B mov eax,dword ptr [ebp-8]
0040D43E push eax
0040D43F push offset string "forTest:%l\n" (00422e80) 0040D444 call printf (0040d6e0)
0040D449 add esp,8
15: }
苦茶粉
0040D44C pop edi
0040D44D pop esi
0040D44E pop ebx
0040D44F add esp,4Ch
0040D452 cmp ebp,esp
0040D454 call __chkesp (0040d6a0)
0040D459 mov esp,ebp
0040D45B pop ebp
0040D45C ret
--- No source file -------------------------------------------------------------------------------------------------------
分析:
0040D3F0~0040D406: 保存栈现场总共10条指令
0040D408: 迭代次数总共1条指令
0040D40F: 保存加法结果总共1条指令
0040D416~0040D439: for循环总共12条指令
0040D43B~0040D449: 打印结果总共5条指令
0040D44C~0040D45C: 恢复栈现场总共9条指令
合计: 38条指令
程序中⼆个⽅法语句区别在于⼀个是for循环,⼀个是while循环.
对应于，查看到上述⼆段汇编指令段while循环⽐for循环少了⼆条指令.
程序中for循环⽤的是传统写法，做下更改将for(int i=0;i0;)，其汇编指令为:
网带窑--- D:\VC\ForWhile\ForWhile.cpp ------------------------------------------------------------------------------------------4: void forTest()
5: {
0040D3F0 push ebp
0040D3F1 mov ebp,esp
0040D3F3 sub esp,48h
0040D3F6 push ebx
0040D3F7 push esi
0040D3F8 push edi
防伪胶带0040D3F9 lea edi,[ebp-48h]
0040D3FC mov ecx,12h
0040D401 mov eax,0CCCCCCCCh
0040D406 rep stos dword ptr [edi]
6: int num = 1234;
0040D408 mov dword ptr [ebp-4],4D2h
cnc真空吸盘7: long sum = 0;
