C++核心準(zhǔn)則C.41:構(gòu)造函數(shù)生成的對(duì)象應(yīng)該被完全初始化

A constructor establishes the invariant for a class. A user of a class should be able to assume that a constructed object is usable.

構(gòu)造函數(shù)有責(zé)任為類(lèi)建立不變式。類(lèi)的用戶應(yīng)該可以假設(shè)構(gòu)造出的對(duì)象式可用的。

class X1 {
 ? ?FILE* f; ? // call init() before any other function
 ? ?// ...
public:
 ? ?X1() {}
 ? ?void init(); ? // initialize f
 ? ?void read(); ? // read from f
 ? ?// ...
};

void f()
{
 ? ?X1 file;
 ? ?file.read(); ? // crash or bad read!
 ? ?// ...
 ? ?file.init(); ? // too late
 ? ?// ...
}

Compilers do not read comments.

編譯器不會(huì)讀注釋。

If a valid object cannot conveniently be constructed by a constructor, use a factory function.

如果不能方便地通過(guò)構(gòu)造函數(shù)構(gòu)建合法的對(duì)象，使用一個(gè)工廠函數(shù)。

• (Simple) Every constructor should initialize every member variable (either explicitly, via a delegating ctor call or via default construction).

  (簡(jiǎn)單)所有的構(gòu)造函數(shù)應(yīng)該初始化所有的成員變量(無(wú)論是明確地通過(guò)委托構(gòu)造函數(shù)，還是默認(rèn)構(gòu)造)

• (Unknown) If a constructor has an Ensures contract, try to see if it holds as a postcondition.

  (不明)如果構(gòu)造函數(shù)包含Ensures協(xié)議，盡量確認(rèn)是否包含了所有的前置條件。

If a constructor acquires a resource (to create a valid object), that resource should be released by the destructor. The idiom of having constructors acquire resources and destructors release them is called RAII ("Resource Acquisition Is Initialization").

如果構(gòu)造函數(shù)請(qǐng)求了資源(為了生成合法的對(duì)象)，那個(gè)資源應(yīng)該被析構(gòu)函數(shù)釋放。構(gòu)造函數(shù)申請(qǐng)資源然后析構(gòu)函數(shù)釋放它們的做法被稱為RAII("資源申請(qǐng)即初始化")。

https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#c40-define-a-constructor-if-a-class-has-an-invariant

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