CPP课件第1章C++概述幻灯片.pptVIP

* There are two problems with the use of preprocessor macros in C++. The first is also true with C: a macro looks like a function call, but doesn’t always act like one. This can bury difficult-to-find bugs. The second problem is specific to C++: the preprocessor has no permission to access class member data. This means preprocessor macros cannot be used as class member functions. To retain the efficiency of the preprocessor macro, but to add the safety and class scoping of true functions, C++ has the inline function. * When you use inline function, the compiler checks to ensure the call is correct and the return value is being used correctly, and then substitutes the function body for the function call, thus eliminating the overhead. (The inline function reduce the time of a function call and thus preserve the efficiency.) The inline code does occupy space, but if the function is small, this can actually take less space than the code generated to do an ordinary function call (pushing arguments on the stack and doing the CALL). 函数原型的作用 C++语言是强类型化语言，任何函数在使用以前必须有该函数的原型说明，以便进行实际参数与形式参数之间的类型匹配检查。 函数返回值的类型和函数参数的类型、个数、次序在函数声明，函数定义和函数调用时必须匹配。 C++语言的编译器执行上述检查能显著减少很多隐藏的错误。 函数原型与C语言的函数类型说明 函数原型是在C语言的函数类型说明（函数声明）的基础上进行扩充后形成的， 它不但说明了函数返回值的类型，还要确定函数参数的类型、个数、次序及缺省值。 1.3.5 　带缺省参数的函数 例如：以下函数带有一个缺省值为0的参数。 void myfunc（double d=0.0） { … } myfunc(198.234); // pass an explicit value myfunc( ); // let function use default 缺省参数的例子 void DrawCircle(int x,int y,int r=10); DrawCircle(50,20); DrawCircle(50,100,30); 带缺省参数函数主要由两个作用：简化编程；有利于程序扩充，而不影响原有代码。 1.3.6 　函数名重载（overload ） 两或两个以上的函数共享同一个名称，就称为函数名重载。 Overloaded Functions Multiple functions can have the same name with different implementations. 函数重载简化了函数调用工作。 函数重载的例子 #include iostream.h ? //Overload abs( ) three ways ? int abs(int n); long abs(long n); double abs(double n); //prototype is neccessary for C++ compiler 这些都是函数原型 函数重载的例子 main( ) { coutAbsolute value of -10:abs(-10)\n; coutAbsolute value of -10L:abs(-10L)\n; cout