推荐回答（5个）
简单理解头文件就是让你的代码知道哪些东西是存在的，你是可以使用的。所以使用任何自定义、系统的函数、类等，都必须先包含头文件，否则编译器就告诉你***不存在。就是这个意思。
库的含义就是在头文件中声明的那些内容对应的实现是怎么样的。这些内容对客户是不需要可见的，只是在程序编译的时候，链接到客户的代码中即可，在运行的时候会加载到客户的进程中。
换句话说，库里边的内容是程序执行的关键。
库文件：是C++已经封装好的一些基本算法功能。你只需引入相应库文件的头文件，调用库文件的函数接口就可以实现相应的功能。这就像你引入iostream.h这个头文件，就可以调用其标准库std下的cout函数进行输出一样。
头文件：你调用库文件里的函数就的调入相应的头文件（虽然标准C++里取消了.h，多了using namespace）.而且头文件你也可以自己定义。
个人认为头文件就是库提供给用户的接口,用户通过调用头文件里声明的函数接口,进而调用库
库文件通过头文件向外导出接口。用户通过头文件找到库文件中
函数实现的代码从而把这段代码链接到用户程序中去。
Most header files contain the declarations of the classes or the functions, and the library files are the implements of the class and functions. You include the header files and link the library files to make sure that your applications can be compiled and linked.
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