可变参模板定义了第一个参数，然后其余参数可以不用确定数量和类型直接打包放在types里面
#include <iostream>
#include <bitset>
using namespace std;
void print(){} //递归函数的出口
template<typename T, typename... types>
void print(const T& firArg, const types&... args){
cout<< firArg <<endl;
//cout << sizeof...(args);
print(args...); // 调用其余参数
}
template<typename... types>
void print(const types&... args){
}
int main()
{
print(7.5,"hello", bitset<8>(233),42);
return 0;
}结果为：
7.5
hello
11101001
42
#include <iostream>
#include <tuple>
using namespace std;
template<typename... Values> class tuple;
template<> class tuple<>{};
template<typename Head, typename... Tail>
class tuple<Head,Tail...>:private tuple<Tail...>
{
typedef tuple<Tail...> inherited;
public:
tuple(){}
tuple(Head v, Tail... vTail):m_head(v), inherited(vTail...){}
typename Head::type head(){
return m_head;
}
inherited& tail(){
return *this;
}
protected:
Head m_head;
}
int main()
{
tuple<int, float, string> t;
t(41,6.3,"nico");
t.Head();
t.tail();
t.tail().head();
return 0;
}这个的本质是array容器
初始化列表不会限制参数的个数，但是参数的类型必须一致，
#include <iostream>
using namespace std;
int i{};
int main()
{
cout<<i; //默认为0
return 0;
}#include <iostream>
//#include <initializer_list>
using namespace std;
void print(initializer_list<int> vals){
for (auto p = vals.begin(); p!= vals.end(); ++p){
cout<< *p << endl;
}
}
int main()
{
print({12,3,5,5,6,8});
return 0;
}#include <iostream>
#include <initializer_list>
using namespace std;
class P{
public:
P(int a, int b) {
cout << "p(int, int),a = " << a <<", b = " << b << endl;
}
P(initializer_list<int> init){
cout <<"p(init,valus = ";
for (auto i : init)
cout << i << ' ';
cout << endl;
}
};
int main()
{
P p(5,6);
P q{5,6};
P r{2,3,4};
P s = {77, 5};
return 0;
}如果去掉P的初始化列表形式，这样写的话也是对的，但是必须参数个数一致。
#include <iostream>
#include <initializer_list>
using namespace std;
class P{
public:
P(int a, int b) {
cout << "p(int, int),a = " << a <<", b = " << b << endl;
}
/* P(initializer_list<int> init){
cout <<"p(init,valus = ";
for (auto i : init)
cout << i << ' ';
cout << endl;
}*/
};
int main()
{
P p(5,6);
P q{5,6};
//P r{2,3,4};
P s = {77, 5};
return 0;
}结果为：
p(int, int),a = 5, b = 6
p(int, int),a = 5, b = 6
p(int, int),a = 77, b = 5初始化列表在C++11之后基本都内置了.比如vector等等。
下面是内置的比较大小，比较起来不会限制比较的数量多少。
#include <iostream>
//#include <initializer_list>
#include <algorithm>
using namespace std;
int main()
{
cout << max({"233","23","33","44"}) << endl;
cout << min({"233","23","33","44"}) << endl;
cout << max({"ab","abc","ace"}) << endl;
cout << min({"ab","abc","ace"}) << endl;
cout << max({233,23,33,44}) << endl;
cout << min({233,23,33,44}) << endl;
return 0;
}结果为：
44
233
ace
ab
233
23运用explict的写法
#include <iostream>
//#include <initializer_list>
#include <algorithm>
using namespace std;
struct Complex{
int real, imag;
explicit Complex(int re, int im = 0):real(re), imag(im){}
Complex operator+(const Complex& x){
return Complex((real + x.real),(imag + x.imag));
}
};
int main()
{
Complex c1(12,5);
Complex c2 = c1 + 5;
cout << c1.real << " " << c1.imag<< endl;
cout << c2.real << " " << c2.imag << endl;
return 0;
}
结果为：
error: no match for ‘operator+’ (operand types are ‘Complex’ and ‘int’)如果去掉了explict就可以直接让复数的实部相加了.这种叫做non-explict one argument 只有这种才可以隐式转换。Complex c2 = c1 + 5;
#include <iostream>
//#include <initializer_list>
#include <algorithm>
using namespace std;
struct Complex{
int real, imag;
Complex(int re, int im = 0):real(re), imag(im){}
Complex operator+(const Complex& x){
return Complex((real + x.real),(imag + x.imag));
}
};
int main()
{
Complex c1(12,5);
Complex c2 = c1 + 5;
cout << c1.real << " " << c1.imag<< endl;
cout << c2.real << " " << c2.imag << endl;
return 0;
}结果为：
12 5
17 5稍微完整的复数的写法
#include <iostream>
//#include <initializer_list>
#include <algorithm>
using namespace std;
struct Complex{
int real, imag;
Complex(int re, int im):real(re), imag(im){}
Complex operator+(const Complex& x){
return Complex((real + x.real),(imag + x.imag));
}
};
int main()
{
Complex c1(12,5);
Complex c2 = c1; //(17, 5)
c2.real = c1.real + 5;
c2.imag = c1.imag + 5;
cout << c1.real << " " << c1.imag<< endl;
cout << c2.real << " " << c2.imag << endl;
return 0;
}结果为：
12 5
17 10
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