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It is deeply recognized that the compiler can cause differences in the compilation results

2022-08-09 16:17:00 【Huang Duoyan】

I used to think that as long as it is a windows system, I am in C language, the api is the same, and the compilation result will be the same.But after reading the practice of netizens and combining my own observations, I strengthened my understanding of the content of the textbook.

Code first:

#include#pragma warning(disable:4996)//If you use devc++, you don't need this linemain(){int count = 0;char i;printf("Enter a number string consisting of 0 and 1, press ctrl+z to end...");while (scanf("%c", &i) != EOF)if (i == '1')count++;printf("You entered %d 1s.", count);}

The picture above shows the result of compiling with vs, and the picture below shows the result of compiling with devc++.Note that the exe compiled with vs is about half the size of devc++.

Next, look at the disassembly.

This is very obvious.The program compiled with vs performs a series of operations on the registers rbp, rdi, rsp, rcx, rax before calling the first sub-process, that is, before executing the call instruction; and using devc++ on the two registers rsp, raxand memory operation.And it can be found that the subtrahend of the subtraction operation on rsp is also different.

Look at the difference in the loaded dll again.

Written in vs:Written in devc++:
"cTest.exe" (Win32): "D:\Programming\cTest\x64\Debug\cTest.exe" loaded.Symbols loaded.
"cTest.exe" (Win32): "C:\Windows\System32\ntdll.dll" loaded.
"cTest.exe" (Win32): "C:\Windows\System32\kernel32.dll" loaded.
"cTest.exe" (Win32): "C:\Windows\System32\KernelBase.dll" loaded.
"cTest.exe" (Win32): "C:\Windows\System32\vcruntime140d.dll" loaded.
"cTest.exe" (Win32): "C:\Windows\System32\ucrtbased.dll" loaded.		"test.exe" (Win32): "D:\Programming\devctest\test.exe" loaded.
"test.exe" (Win32): "C:\Windows\System32\ntdll.dll" loaded.
"test.exe" (Win32): "C:\Windows\System32\kernel32.dll" loaded.
"test.exe" (Win32): "C:\Windows\System32\KernelBase.dll" loaded.
"test.exe" (Win32): "C:\Windows\System32\msvcrt.dll" loaded.

I checked online and found that vcruntime140d.dll is from visual c++ redistributable:

There is also ucrtbased.dll. Note that if you copy these two programs directly to another computer, the ones written in vs will not work properly.I will explore this further when I have time.

So it's true in the textbook that the compiler is also a factor that affects the results of program execution.

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