C++隱式推導-auto關鍵詞

{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"總述"}]},{"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++中有一個關鍵字，它不進行顯式聲明，而進行隱式推導，auto可以在聲明變量時根據變量初始值的類型自動爲此變量選擇匹配的類型。C++語言類似的關鍵字還有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":"如何評價 C++ 11 auto 關鍵字？"},{"type":"text","text":"既然auto關鍵字可以用來做類型推斷，使得C++在使用auto時更像是在用動態類型語言。既然auto能幫我們偷很多懶，那平時寫C++還有必要像之前一樣顯式聲明類型嗎？最佳實踐是如何，應當徹底改變之前的C++習慣儘可能大量地使用auto，還是在什麼樣的特定的情形下才使用auto？知乎問答"}]}]},{"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":"知乎上有這麼一條問題很有意思，大家對於auto使用有很多的討論，接下來我就一點點解開auto的神祕面紗，讓大家來進行評判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：良知猶存"}]},{"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":"轉載授權以及圍觀：歡迎添加微信公衆號：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":"先上一段小代碼："}]},{"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":"從上面可以看到，我們聲明不需要定義顯性的類型，只需要用auto定義進行自動推導即可。"}]},{"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":" 編程時經常需要把表達式的值賦給變量，這就要求聲明變量的時候，我們可以清楚的知道表達式的類型。然而很多時候"},{"type":"text","marks":[{"type":"strong"}],"text":"名字空間、模板"},{"type":"text","text":"成爲類型的一部分，導致了程序員在複雜類型的初始化聲明中如履薄冰，所以C++11中引入了auto類型說明符，用它就可以讓編譯器替我們分析表達式所屬的類型。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"簡潔之道："}]},{"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":"舉一個經常使用的容器的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定義變量i，在c++中是一個安全可靠的方法，但是名字也是很長，如果用auto的話，代碼會簡潔很多。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函數對象"}]},{"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.函數的返回類型（auto在C++14可以作爲函數返回類型）"}]},{"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":" 這就是我分享的auto關鍵詞，如果大家有什麼更好的思路，歡迎分享交流哈。"}]},{"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，掃碼關注我"}]},{"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}}]}