C++中 #include<>与#include""

#include<>

使用尖括号表示在包含文件目录中去查找(包含目录是由用户在设置环境时设置的)，而不在源文件目录去查找；

#include""

使用双引号则表示首先在当前的源文件目录中查找，若未找到才到包含目录中去查找；

MSDN的相关说明

  #include""

      This form instructs the preprocessor to look for include files in the same directory of the file that contains the #include statement, and then in the directories of any files that include (#include) that file. The preprocessor then searches
along the path specified by the /I compiler option, then along paths specified by the INCLUDE environment variable.

  #include<>

      This form instructs the preprocessor to search for include files first along the path specified by the /I compiler option, then, when compiling from the command line, along the path specified by the INCLUDE environment variable.

扩展知识

Q：C++中的预处理#include<iostream>和#include<iostream.h>对程序的运行有什么不同？

A：没有区别

Q：#include<iostream>后加using namespace std; 和直接用#include<iostream.h>在运行上有什么区别？

A：#include<iostream.h>是早些时候的形式

      最新的标准定义的是

      #include<iostream>

      using namespace std;

      比如#include<math.h>变成

      #include<cmath>

      using namespace std;

      #include<string.h>变成

      #include<cstring>

using namespace std;

from：http://blog.csdn.net/xiaoting451292510/article/details/12562363

巴特西

C++中 #include<>与#include""

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