c++语言特性

《现代c++语言核心特性解析》学习笔记（一）

#include ``
#include ``
#include ``

int main(int argc, char *argv[])
{
	std::cout << "Hello world!" << std::endl;

	std::cout << "long long max: " << std::numeric_limits``::max() << std::endl;
	std::cout << "long long min: " << std::numeric_limits``::min() << std::endl;
	std::cout << "unsigned long long max: " << std::numeric_limits``::max() << std::endl;

    	std::printf("llong_max: %lldn", std::numeric_limits``::max());
	std::printf("llong_min: %lldn", std::numeric_limits``::min());
	std::printf("unsigned llong_max: %llun", std::numeric_limits``::max());
}

Hello world!
long long max: 9223372036854775807
long long min: -9223372036854775808
unsigned long long max: 18446744073709551615
llong_max: 9223372036854775807
llong_min: -9223372036854775808
unsigned llong_max: 18446744073709551615
Executing run: all complete!

#include 
#include 
#include 

namespace A::inline B::inline C 
{
	char foo() {
		return u8'c';
	}
}

namespace A::inline B::D
{
	char foo() {
		return u8'd';
	}
}

// namespace A::inline B   // 编译错误
// { 
// 	char foo() {
// 		return u8'e';
// 	}
// }
namespace A::E
{
	char foo() {
		return u8'e';
	}
}

int main(int argc, char *argv[])
{
	std::cout << "Hello world!" << std::endl;

	auto a = A::foo();
	std::cout << "auto type: " << a << std::endl;  //c
	a = A::B::foo();
	std::cout << "auto type: " << a << std::endl;  //c
	a = A::B::D::foo();
	std::cout << "auto type: " << a << std::endl;  //d
	a = A::E::foo();
	std::cout << "auto type: " << a << std::endl;  //e
}

推导规则，从左向右，往上推导；

auto i = true ? 5:8.0;
	std::cout << "auto type:" << typeid(i).name() << std::endl;   // double

函数形参列表中可以使用，c++17后

void echo(auto str) {
	std::cout << "echo auto type:" << typeid(str).name() << std::endl;
}

int main(int argc, char *argv[])
{
	echo("string");
	echo(10);
	echo(10.0);
}

auto type:d
echo auto type:PKc
echo auto type:i
echo auto type:d

各种推导规则：

	int i = 5 ;
	int &j = i;
	auto &m = j;
	i++;
	std::cout << i << j << m << std::endl;

	auto&& n = i; //int &
	i++;
	auto&& k = 5; //int &&
	std::cout << i << n << k << std::endl;

	auto i1 = {1, 2};
	auto i2{1};
	auto i3 = {1};
	auto i4 = [](){;};

	std::cout << "auto type: " << typeid(i1).name() << std::endl;
	std::cout << "auto type: " << typeid(i2).name() << std::endl;
	std::cout << "auto type: " << typeid(i3).name() << std::endl;
	std::cout << "auto type: " << typeid(i4).name() << std::endl;

666
775
auto type: St16initializer_listIiE
auto type: i
auto type: St16initializer_listIiE
auto type: Z4mainEUlvE_

类继承时推导

class Base {
public:
	virtual void foo() {
		std::cout << "call base foo:" << std::endl;
	}
};
class Derived: public Base {
public:
	virtual void foo() override {
		std::cout << "call derivced foo:" << std::endl;
	}
};
int main(int argc, char *argv[])
{
	Base *b = new Derived();
	b->foo();
	auto e = b;
	e->foo();
	auto &f = b;
	f->foo();
	auto d = *b;
	d.foo();
	auto &c = *b;
	c.foo();
	auto *h = &d;
	h->foo();
	auto *m = &(*b);
	m->foo();
	auto n = *&b;
	n->foo();
}

call derivced foo:
call derivced foo:
call derivced foo:
call base foo:
call derivced foo:
call base foo:
call derivced foo:
call derivced foo:

lambda的后置返回类型推导

	auto lm = [](int &i)->auto& {return i;};
	auto x1 = 5;
	auto &x2 = lm(x1);
	assert(&x1 == &x2);  // 相同内存地址

非类型模板形参占位符

	f<5>();
	f<'5'>();
	f();
	//f<5.0>();
	//f<{1,2}>();
	//f();

auto type:i
auto type:c
auto type:b