我对编程相当陌生,想问问为什么我用不同的代码得到相同的结果。我实际上正在读一本书,书中的例子是用printf(也在汇编程序中)。在这种情况下,它说<[email protected]>
。本书中的汇编代码与我的不同,但C代码是相同的。我的处理器只是计算不同吗?无论我是否使用printf或puts,它为什么在反汇编时显示放入?
(问题是在呼叫<+34>
<[email protected]>
)
代码1:
#include <stdio.h>
int main()
{
int i;
for(i=0; i<10; i++)
{
printf("Hello, world!\n");
}
return 0;
}
代码2:
#include <stdio.h>
int main()
{
int i;
for(i=0; i<10; i++)
{
puts("Hello, world!\n");
}
return 0;
}
代码1拆卸:
Dump of assembler code for function main:
0x080483eb <+0>: lea ecx,[esp+0x4]
0x080483ef <+4>: and esp,0xfffffff0
0x080483f2 <+7>: push DWORD PTR [ecx-0x4]
0x080483f5 <+10>: push ebp
0x080483f6 <+11>: mov ebp,esp
0x080483f8 <+13>: push ecx
=> 0x080483f9 <+14>: sub esp,0x14
0x080483fc <+17>: mov DWORD PTR [ebp-0xc],0x0
0x08048403 <+24>: jmp 0x8048419 <main+46>
0x08048405 <+26>: sub esp,0xc
0x08048408 <+29>: push 0x80484b0
0x0804840d <+34>: call 0x80482c0 <[email protected]>
0x08048412 <+39>: add esp,0x10
0x08048415 <+42>: add DWORD PTR [ebp-0xc],0x1
0x08048419 <+46>: cmp DWORD PTR [ebp-0xc],0x9
0x0804841d <+50>: jle 0x8048405 <main+26>
0x0804841f <+52>: mov eax,0x0
0x08048424 <+57>: mov ecx,DWORD PTR [ebp-0x4]
0x08048427 <+60>: leave
0x08048428 <+61>: lea esp,[ecx-0x4]
0x0804842b <+64>: ret
End of assembler dump.
代码2拆卸:
Dump of assembler code for function main:
0x080483eb <+0>: lea ecx,[esp+0x4]
0x080483ef <+4>: and esp,0xfffffff0
0x080483f2 <+7>: push DWORD PTR [ecx-0x4]
0x080483f5 <+10>: push ebp
0x080483f6 <+11>: mov ebp,esp
0x080483f8 <+13>: push ecx
0x080483f9 <+14>: sub esp,0x14
0x080483fc <+17>: mov DWORD PTR [ebp-0xc],0x0
0x08048403 <+24>: jmp 0x8048419 <main+46>
=> 0x08048405 <+26>: sub esp,0xc
0x08048408 <+29>: push 0x80484b0
0x0804840d <+34>: call 0x80482c0 <[email protected]>
0x08048412 <+39>: add esp,0x10
0x08048415 <+42>: add DWORD PTR [ebp-0xc],0x1
0x08048419 <+46>: cmp DWORD PTR [ebp-0xc],0x9
0x0804841d <+50>: jle 0x8048405 <main+26>
0x0804841f <+52>: mov eax,0x0
0x08048424 <+57>: mov ecx,DWORD PTR [ebp-0x4]
0x08048427 <+60>: leave
0x08048428 <+61>: lea esp,[ecx-0x4]
0x0804842b <+64>: ret
End of assembler dump.
GNU'gcc'认为用'puts(“some string”)替换'printf(“一些字符串\ n”)''是一个好主意;' - 这样做。这是一个优化; 'puts()'不必解释格式字符串。 –
相关:[可以将printf替换为自动放入C程序?](https://stackoverflow.com/questions/25816659/can-printf-get-replaced-by-puts-automatically-in-ac-program) –
好的谢谢你的帮助! :) –