C++ 11/14/17 Grammar

The goal of new cpp aims at:

  • Make cpp a better language for systems programming and library building

  • Make cpp easier to teach and learn

main()

main() 函数的原型为:

int main(int argc, char** argv) or int main(int argc, char* argv[]).

其中 argc 表示参数的数量,argv 数组为从下标 0 开始的数组,第 0 个参数一般为可运行的文件。

Define Struct

There are many ways to define struct, what we should do is that chose a best way to solve problem.

  • Example 1
struct Point { double x, y; };
double dist(struct Point a, struct Point b){return hypot(a.x-b.x, a.y-b.y);
}
  • Example2
typedef struct { double x, y; } Point;
double dist(Point a, Point b){return hypot(a.x-b.x, a.y-b.y);
}

As you can see from the comparison, Example 2 is better, which use typedef struct { define; }struct name; to define.

lvalue and rvalue

int x = 0;  //x is lvalue
int* p = &++x;  //++x is lvalue, can use &
++x = 10;
p = &x++;   //x++ returns a temperate value,, error!

lvalue can be assigned a value or use '&', rvalue can't.

more information about rvalue reference

#include <iostream>
#include <utility>

int i = 101, j = 101;

int foo(){ return i; }
int&& bar(){ return std::move(i); }
void set(int&& k){ k = 102; }
int main()
{
    foo();
    std::cout << i << std::endl;
    set(bar());
    std::cout << i << std::endl;
}
/*output:
101
102*/

OOP

Q: What is different between difination and declaration?

Usage

member initializer list

class Point {
private:
    const float x,y;
    Point(float xa = 0.0, float ya =0.0) : y(ya), x(xa) {}
};

Templates

Defination

函数模板的例子:



 
 









// 方便阅读,其实可以写成一行
// template <typename T> int compare(const T &v1, const T &v2)
template <typename T>
int compare(const T &v1, const T &v2)
{
    // 使用 less<T> 似的类型无关和可移植
    if (less<T> (v1, v2)) return -1;
    if (less<T> (v2, v1)) return -1;
    return 0;
}

// compare(0, 1)
  • 当我们调用一个函数模板时,编译器通常用函数实参来为我们推断模板实参。
  • 在模板参数列表中, typename 和 class 含义相同,可以互换使用。

the format for declaring function template with type parameters is:

template <class identifier> function_declaration;

template <typename identifier> function_declaration;

its use is indistinct, so both expressions have exactly the same meaning.

Nontype Parameter

非类型参数

  1. 可以在模板中定义非类型参数,一个非类型参数表示一个值而非一个类型。

  2. 非类型参数必须是常量表达式,从而允许编译器在编译时实例化模板;当一个模板被实例化时,非类型参数被一个用户提供的或编译器推断出的值所代替。

一个最典型的应用是 处理任意大小数组的 print 函数:

  • 使用非类型模板

  • 参数为 Arr const &arr (Arr 类型的 arr 引用)

Last Updated: 1/24/2019, 3:26:49 PM