#pragma once 文件编译一次

#pragma once

Specifies that the file will be included (opened) only once by the compiler in a build. This can reduce build times as the compiler will not open and read the file after the first #include of the module.

指定当前文件在构建时只被包含(或打开)一次,这样就可以减少构建的时间,因为加入#pragma once后,编译器在打开或读取第一个#include 模块后,就不会再打开或读取随后出现的相同#include 模块. 一句话#pragma once的意思是要求编译器在编译过程中只将包含此命令文件编译（打开）一次，从而避免重复包含此文件。

For example,

//header.h
#pragma once
// Your C or C++ code would follow: