C++(内联函数与宏定义)

内联函数是C++为提高程序运行速度所做的一项改进。应有选择地使用内联函数，如果代码执行时间很短，内联调用就可以节省非内联调用使用的大部分时间。使用内联函数特性，需要在函数前加上关键字inline。

#include 
#include "my_inline.h"

inline double square(double x) { return x * x; }
#define SQUARE(X) X*X

void my_inline(void)
{
    using namespace std;
    double a, b;
    double c = 13.0, d;

    cout << "***inline test***" << endl;
    a = square(5.0);
    b = square(4.5 + 7.5); //b = (4.5+7.5) * (4.5+7.5) = 144
    cout << "a = " << a << ", b = " << b << "n";
    cout << "c = " << c;
    cout << ", c squared = " << square(c++) << "n"; //c = 13 * 13 = 169
    cout << "now c = " << c << "n";

    cout << "***define test***" << endl;
    c = 13.0;
    a = SQUARE(5.0);
    b = SQUARE(4.5 + 7.5); //b = 4.5 + 7.5 * 4.5 + 7.5 = 45.75
    cout << "a = " << a << ", b = " << b << "n";
    cout << "c = " << c;
    cout << ", c SQUARE = " << SQUARE(c++) << "n"; //c = 13 * 14 = 182
    cout << "now c = " << c << "n";
}

输出：
***inline test***
a = 25, b = 144
c = 13, c squared = 169
now c = 14
***define test***
a = 25, b = 45.75
c = 13, c SQUARE = 182
now c = 15

SQUARE(c++)等价c++*c++
用m代表第一个c++,n代表第二个c++
1. 执行第一个c++即m; m=13, n=13, c=13;
2. 执行第二个c++即n; m=14, n=13, c=14;
3. 执行c++*c++即m*n; m*n=183, c=15;

square(c++)
1. 执行c++; c=14
2. 执行c*c; 14 * 14 = 169; 

内联函数是通过传递参数实现的，宏定义通过文本替换实现。

注：参考C++ Primer Plus第六版P208