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C++使用非常量静态成员(non-const static data member)

但C++支持在类里定义非常量静态成员函数，如"static double average(){...};"。误区二：在函数体内对非常量静态成员变量初始化。...（xcode有提示）正确的方法是将初始化语句放到函数体外定义（在类中只有声明），然后在函数内以class::member的方式调用。 ?...非常量静态成员的错误使用方法综上，非常量静态成员变量需要在类的public中声明，在函数体外类外定义，以classname::member的方式使用。

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C++核心准则讨论：如果在初始化期间需要“虚行为”，请使用工厂函数

Discussion: Use a factory function if you need "virtual behavior" during initialization 讨论：如果在初始化期间需要...member functions virtual calls behave normally....Post-initialize lazily: Do it during the first call of a member function....T> static shared_ptr create() // interface for creating shared objects { auto...Defining several overloads of create can assuage this problem, however; and the overloads can even be templated

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C++ Dos and Donts

Static variables Dynamic initialization of function-scope static variables is thread-safe in Chromium...static int good_count = 42; // Done before dynamic initialization....static auto& object = *new Object; // For class types. } Explicitly declare class copyability/..., except where a member's value is explicitly set by every constructor....Avoid const_cast to remove const, except when implementing non-const getters in terms of const getters

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【static】关键字静态成员：在类级别上共享数据和方法的机制

(as opposed to declaring) a static data member [-fpermissive] static int CBOOK::x =100;...initialization of non-const static member ‘CBOOK::x’ static int x = 102;...^ staticnumbers.cpp:27:13: error: duplicate initialization of ‘CBOOK::x’ int CBOOK::x =100;...^ staticnumbers.cpp:27:16: error: ISO C++ forbids in-class initialization of non-const static member...member function ‘static void CBOOK::cbookfunction()’: staticnumbers.cpp:31:22: error: cannot call member

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Smart Pointer Programming Techniques

as an opaque handle: class FILE; FILE * fopen(char const * name, char const * mode); void fread(FILE...*) const { } }; static X x; shared_ptr createX() { shared_ptr px(&x, null_deleter...: class X { private: X() { ... } public: static shared_ptr create() { shared_ptr...; return px; } }; The solution is to keep a weak pointer to this as a member in impl: class...& operator=(impl const &); impl() { ... } public: static shared_ptr create() {

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C++核心准则C.132:不要没有理由就将函数声明为虚函数‍

A virtual function can be overridden and is thus open to mistakes in a derived class....A virtual function ensures code replication in a templated hierarchy. 多余的虚函数会增加运行时和目标码的大小。...Example, bad(反面示例) templateclass T> class Vector { public: // ......virtual int size() const { return sz; } // bad: what good could a derived class do?...Flag a class where all member functions are virtual and have implementations.

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跟Google学写代码--Chromium工程中用到的C++11特性

TypeName&) = delete; \ TypeName& operator=(const TypeName&) = delete } class Derived...Class Member Initializers 代码一目了然： class S { int n; // non-static data member...int& r; // non-static data member of reference type int a[10] = {1, 2}; // non-static...data member with initializer (C++11) std::string s, *ps; // two non-static data members struct...(bool, string) #include template class T> void swap(T& a, T& b) { static_assert(std

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C++、Java语法差异对照表

the destructor Static member functions and variables 静态函数和变量 Same as method declarations, but Java...provides static initialization blocks to initialize static variables (instead of putting a definition...in a source code file): class Foo { static private int x; // static initialization block...refer to a static method, you use the form Class::method....C++ bool foo; Java boolean foo; Const-ness(常量性) C++ const int x = 7; Java final int x = 7; Throw

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C++核心准则讨论：按照成员声明的顺序定义和初始化成员变量

Discussion: Define and initialize member variables in the order of member declaration 讨论：按照成员声明的顺序定义和初始化成员变量...Member variables are always initialized in the order they are declared in the class definition, so write...them in that order in the constructor initialization list....class Employee { string email, first, last; public: Employee(const char* firstName, const char...* lastName); // ... }; Employee::Employee(const char* firstName, const char* lastName) : first

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C++核心准则C.42:如果构造函数不能生成合法对象就抛出异常

Example（示例） class X2 { FILE* f; // ... public: X2(const string& name) :f{fopen(name.c_str...Zeno"}; // throws if file isn't open file.read(); // fine // ... } Example, bad（反面示例） class...FILE* f; // call is_valid() before any other function bool valid; // ... public: X3(const...work in a constructor has been to avoid code replication.Delegating constructors and default member...initialization do that better.

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C++核心准则NR.5：不要使用两阶段初始化

NR.5: Don't use two-phase initialization NR.5：不要使用两阶段初始化 Reason（原因） Splitting initialization into two...= x; // also bad: assignment in constructor body // rather than in member...// rather than in member initializer } ~Picture() { Cleanup...Example, good（范例） class Picture { int mx; int my; vector data; static int check_size...Alternative（代替选项） Always establish a class invariant in a constructor. 始终在构造函数中建立类不变式。

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现代C++之SFINAE

函数指针 -> std::string serialize() const template static yes &test(reallyHasstatic const bool value = sizeof(test(0)) == sizeof(yes); // 或者 // enum { value = sizeof(test...现在我们可以在“template class T> std::string serialize(const T& obj)”签名上使用这个错误来调度到正确的版本。...(const T& obj) { return obj.serialize(); } template class T> typename enable_if<!...测试如下： templateclass T> std::string serialize(const T &obj) { // 不加constexpr 报错：error: no member

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C++核心准则C.131: 避免无意义的getters和setters‍

Example(示例) class Point { // Bad: verbose int x; int y; public: Point(int xx, int yy) :...x{xx}, y{yy} { } int get_x() const { return x; } void set_x(int xx) { x = xx; } int get_y...() const { return y; } void set_y(int yy) { y = yy; } // no behavioral member functions }; Consider...making such a class a struct -- that is, a behaviorless bunch of variables, all public data and no member...: C.49: Prefer initialization to assignment in constructors.

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C++17 New Features

const int sValue = 777; }; The advantage of inline over constexpr is that your initialization expression...Lambda capture of *this this pointer is implicitly captured by lambdas inside member functions....Aggregate initialization of classes with base classes If a class was derived from some other type you...couldn’t use aggregate initialization....Direct-list-initialization of enumerations You can now initialize enum class with a fixed underlying

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C++核心准则T.62：将非依赖类模板成员放入非模板基类中

T.62: Place non-dependent class template members in a non-templated base class T.62：将非依赖类模板成员放入非模板基类中...// ... }; Note（注意） A more general version of this rule would be "If a class template member depends on...only N template parameters out of M, place it in a base class with only N parameters."...For N == 1, we have a choice of a base class of a class in the surrounding scope as in T.61....class statics? 本规则的更普遍版是：如果模板类成员只依赖于M以外的N个模板参数，将其放入只包含N个参数的基类中。

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C++那些事之SFINAE

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C++箴言：理解typename的两个含义

如果 C 有一个 static data member（静态数据成员）碰巧就叫做 const_iterator 呢？再如果 x 碰巧是一个 global variable（全局变量）的名字呢？...dependent type names"（“typename 必须前置于嵌套依赖类型名”）规则的例外是 typename 不必前置于在一个 list of base classes（基类列表）中的或者在一个 member...initialization list（成员初始化列表）中作为一个 base classes identifier（基类标识符）的 nested dependent type name（嵌套依赖类型名...对于像 value_type 这样的 traits member names（特性成员名），一个通用的惯例是 typedef name 与 traits member name 相同，所以这样的一个 local...·用 typename 去标识 nested dependent type names（嵌套依赖类型名），在 base class lists（基类列表）中或在一个 member initialization

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Chapter 3: Moving to Modern C++

() if( static_cast(c) < 14.5 ){ // valid auto factors = primeFactors(static_castconst member functions thread safe 11....Summary Braced initialization is the most widely usable initialization syntax, it prevents narrowing...Make const member functions thread safe unless you're certain they'll never be used in a concurrent context...Member function templates never suppress generation of special member functions.

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Spring Boot Actuator

artifactId> 开始使用Actuator 配好上面的依赖之后，我们使用下面的主程序入口就可以使用Actuator了： @SpringBootApplication public class...ActuatorApp { public static void main(String[] args) { SpringApplication.run(ActuatorApp.class...我们看下怎么自定义HealthIndicator： @Component public class CustHealthIndicator implements HealthIndicator {...status":"UP"} } 在Spring Boot 2.X之后，Spring添加了React的支持，我们可以添加ReactiveHealthIndicator如下： @Component public class...或者@EndpointJmxExtension）来实现对现有EndPoint的扩展： @Component @EndpointWebExtension(endpoint = InfoEndpoint.class

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Spring Boot 运行源码剖析

MyApplication { public static void main(String[] args) { SpringApplication.run(MyApplication.class...INFO 4205 --- [ restartedMain] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization...":false},"health":{"href":"http://localhost:8080/actuator/health","templated":false},"health-path":{"...href":"http://localhost:8080/actuator/health/{*path}","templated":true},"info":{"href":"http://localhost...:8080/actuator/info","templated":false}}} 小结依稀还记得 2011 年那会儿，Spring 还没有现在这么流行。

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C++使用非常量静态成员(non-const static data member)

C++核心准则讨论：如果在初始化期间需要“虚行为”，请使用工厂函数

C++ Dos and Donts

【static】关键字静态成员：在类级别上共享数据和方法的机制

Smart Pointer Programming Techniques

C++核心准则C.132:不要没有理由就将函数声明为虚函数‍

跟Google学写代码--Chromium工程中用到的C++11特性

C++、Java语法差异对照表

C++核心准则讨论：按照成员声明的顺序定义和初始化成员变量

C++核心准则C.42:如果构造函数不能生成合法对象就抛出异常

C++核心准则NR.5：不要使用两阶段初始化

现代C++之SFINAE

C++核心准则C.131: 避免无意义的getters和setters‍

C++17 New Features

C++核心准则T.62：将非依赖类模板成员放入非模板基类中

C++那些事之SFINAE

C++箴言：理解typename的两个含义

Chapter 3: Moving to Modern C++

Spring Boot Actuator

Spring Boot 运行源码剖析

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