C++隐式推导-auto关键词

{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"总述"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"C++中有一个关键字，它不进行显式声明，而进行隐式推导，auto可以在声明变量时根据变量初始值的类型自动为此变量选择匹配的类型。C++语言类似的关键字还有decltype。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"如何评价 C++ 11 auto 关键字？"},{"type":"text","text":"既然auto关键字可以用来做类型推断，使得C++在使用auto时更像是在用动态类型语言。既然auto能帮我们偷很多懒，那平时写C++还有必要像之前一样显式声明类型吗？最佳实践是如何，应当彻底改变之前的C++习惯尽可能大量地使用auto，还是在什么样的特定的情形下才使用auto？知乎问答"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"知乎上有这么一条问题很有意思，大家对于auto使用有很多的讨论，接下来我就一点点解开auto的神秘面纱，让大家来进行评判auto。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"作者：良知犹存"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"转载授权以及围观：欢迎添加微信公众号：Conscience_Remains"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"先上一段小代码："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"auto f = 3.14; //double\nauto s(\"hello\"); //const char*\nauto z = new auto(9); //int *"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"从上面可以看到，我们声明不需要定义显性的类型，只需要用auto定义进行自动推导即可。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 编程时经常需要把表达式的值赋给变量，这就要求声明变量的时候，我们可以清楚的知道表达式的类型。然而很多时候"},{"type":"text","marks":[{"type":"strong"}],"text":"名字空间、模板"},{"type":"text","text":"成为类型的一部分，导致了程序员在复杂类型的初始化声明中如履薄冰，所以C++11中引入了auto类型说明符，用它就可以让编译器替我们分析表达式所属的类型。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"简洁之道："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"举一个经常使用的容器的iterator的例子："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"#include   \n#include \nvoid test(std::vector<:string>&vs) \n{ \n std::vector<:string>::iterator i=vs.begin(); \n    for(;i::iterator定义变量i，在c++中是一个安全可靠的方法，但是名字也是很长，如果用auto的话，代码会简洁很多。如下：​​​​​​​"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"#include \n#include \nvoid test(std::vector<:string>&vs)\n{\n  for(  auto i=vs.begin();;i函数对象"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"3.函数的返回类型（auto在C++14可以作为函数返回类型）"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"template\nauto fun(T x,U y)\n{\n return x*y;\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 这就是我分享的auto关键词，如果大家有什么更好的思路，欢迎分享交流哈。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/27/27cc21ae87cd8cb2b284f34579495cc3.jpeg","alt":"","title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ab/ab5da14454a25c1453ae843c88b07540.gif","alt":null,"title":"Click and drag to move","style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"​"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"更多分享，扫码关注我"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}