说明：  C语言函数速查手册，如果突然想用C语言的某个函数，但又忘了该函数如何调用，可以从手册里快速查询到该函数的原型和用法
(C language function manual, if you suddenly want to use a certain function of C language, but forgot how to call the function, can the manual fast query to the prototype and the usage of the function)