C++关键字全集

loop or conditional statement in which it appears.(7)caseswitch语句分支.Labels that appear after the case keyword cannot also appear outside a switch statement.(8)catch,throw,try都是异常处理的语句,The try, throw, and catch statements implement exception handling.(9)char声明字符型变量或函数.(10)class声明或定义类或者类的对象.The class keyword declares a class type or defines an object of a class type.(11)const被const修饰的东西都受到强制保护，可以预防意外的变动，能提高程序的健壮性。

它可以修饰函数的参数、返回值，甚至函数的定义体。

作用:1.修饰输入参数a.对于非内部数据类型的输入参数，应该将“值传递”的方式改为“const引用传递”，目的是提高效率。

例如将void Func(A a) 改为void Func(const A &a)。

b.对于内部数据类型的输入参数，不要将“值传递”的方式改为“const引用传递”。

否则既达不到提高效率的目的，又降低了函数的可理解性。

例如void Func(int x) 不应该改为void Func(const int &x)。

2.用const修饰函数的返回值a.如果给以“指针传递”方式的函数返回值加const修饰，那么函数返回值（即指针）的内容不能被修改，该返回值只能被赋给加const修饰的同类型指针。

如对于：const char * GetString(void);如下语句将出现编译错误：char *str = GetString();//cannot convert from 'const char *' to 'char *'；正确的用法是：const char *str = GetString();b.如果函数返回值采用“值传递方式”，由于函数会把返回值复制到外部临时的存储单元中，加const修饰没有任何价值。

如不要把函数int GetInt(void) 写成const int GetInt(void)。

3.const成员函数的声明中，const关键字只能放在函数声明的尾部,表示该类成员不修改对象. 说明：const type m; //修饰m为不可改变示例：typedef char * pStr; //新的类型pStr;char string[4] = "abc";const char *p1 = string；p1++; //正确，上边修饰的是*p1,p1可变const pStr p2 = string;p2++; //错误，上边修饰的是p2，p2不可变,*p2可变同理，const修饰指针时用此原则判断就不会混淆了。

const int *value; //*value不可变，value可变int* const value; //value不可变，*value可变const (int *) value; //(int *)是一种type,value不可变,*value可变//逻辑上这样理解，编译不能通过，需要tydef int* NewType;const int* const value;//*value,value都不可变(12)continue结束当前循环，开始下一轮循环.Forces transfer of control to the controlling expression of the smallest enclosing do, for, or while loop.(13)defaultswitch语句中的默认分支.None of the constants match the constants in the case labels;a default label is present.Control is transferred to the default label.(14)delete经常用于动态内存分配的语句,Deallocates a block of memory.(15)do在do-while循环结构中开始循环体.Executes a statement repeatedly until the specified termination condition (the expression) evaluates to zero.(16)double声明双精度变量或函数.(17)else条件语句否定分支(与if 连用).(18)enum声明枚举类型.The name of each enumerator is treated as a constant and must be unique within the scope where the enum is defined.(19)explicitThis keyword is a declaration specifier that can only be applied to in-class constructor declarations. An explicit constructor cannot take part in implicit conversions. It can only be used to explicitly construct an object.(20)exportMSDN只说The export keyword is not supported on templates.一种导出语句吧..(21)externextern 意为“外来的”···它的作用在于告诉编译器：有这个变量，它可能不存在当前的文件中，但它肯定要存在于工程中的某一个源文件中或者一个Dll的输出中。

声明变量是在其他文件中声明(也可以看做是引用变量).Objects and variables declared as extern declare an object that is defined in another translation unit or in an enclosing scope as having external linkage.(22)false,truebool类型的两个枚举值.(23)float声明浮点型变量或函数.(24)for一种循环语句(可意会不可言传).Use the for statement to construct loops that must execute a specified number of times.(25)friend声明友元函数或者类.The friend keyword allows a function or class to gain access to the private and protected members of a class.(26)goto无条件跳转语句.Performs an unconditional transfer of control to the named label.(27)if条件语句.Controls conditional branching.常与else一起用.(28)inline声明定义内联函数,编译时将所调用的代码嵌入到主函数中.The inline specifiers instruct the compiler to insert a copy of the function body into each place the function is called.(29)int声明整型变量或函数.(30)long声明长整型变量或函数.(31)mutableThis keyword can only be applied to non-static and non-const data members of a class. If a data member is declared mutable, then it is legal to assign a value to this data member from a const member function.(32)namespaceDynamically imports an element behavior into a document.(33)new动态内存分配.Allocates memory for an object or array of objects of type-name from the free store and returns a suitably typed, nonzero pointer to the object.(34)operatorThe operator keyword declares a function specifying what operator-symbol means when applied to instances of a class.(35)private类私有函数和数据成员的标示.When preceding a list of class members, the private keyword specifies that those members are accessible only from member functionsand friends of the class. This applies to all members declared up to the next access specifier or the end of the class.(36)protectedThe protected keyword specifies access to class members in the member-list up to the next access specifier (public or private) or the end of the class definition.(37)publicWhen preceding a list of class members, the public keyword specifies that those members are accessible from any function. This applies to all members declared up to the next access specifier or the end of the class.(38)register声明积存器变量.The register keyword specifies that the variable is to be stored in a machine register, if possible.这个关键字命令编译器尽可能的将变量存在CPU内部寄存器中,而不是通过内存寻址访问,从而提高效率。