Differences between pragma and ifndef

First #pragma once It's compiler related , Some compilers support , Some compilers don't support

1、#ifndef The method depends on the macro name and cannot conflict , So this ensures that the same file will not be included more than once , It also ensures that multiple copies of files will not be included at the same time ;
The disadvantage is that if the macro names of different content header files are not careful “ Car crash ”, The compiler can only contain one of them ;
2、#pragma once Is guaranteed by the compiler ： The same file will not be compiled more than once . Pay attention to what's said here “ The same file ” It's a physical file ;
Weakness is , There are multiple copies of a header file , This method cannot guarantee that they are not included repeatedly .

3、 Sum up ,#ifndef Ensure that the macro name does not duplicate ;
#pragma once Ensure that the physical files are not duplicated ;