Effective Modern C++[实践]-＞理解auto类别推导

1. 一般情况，auto推导与模板类型推导一致，唯一不同是auto可使用{}进行推导，模板不行
2. c++14在函数返回值或者lambda形参中使用auto时，使用的是模板推导而不是auto推导，因此{}使用需注意

#include <stdio.h>
#include <stdlib.h>
#include <iostream>

using namespace std;

void someFunc(){

}
template<typename T>
void f0(T value){

}

template<typename T>
void f(std::initializer_list<T> value){

}
int main() {
    auto x = 5;            
    const auto cx = x; //既非指针也非引用   
    const auto &rx = x; //const 引用
  	const auto *ptx = &x;//const 指针
    auto &rx1 = x; //引用
  	auto *ptx1 = &x;//指针
  
  
    auto&& uref1 = 5;   //右值 
  	auto&& uref2 = x;   // x是左值，
    auto&& uref3 = cx;   
    auto&& uref4 = rx;  

    auto func1 = someFunc; //退化为函数指针
    auto& func2 = someFunc;  // 函数引用
  
  	const char text[]="xi men 吹雪";
  	auto arr1 = text;//退化为指针
  	auto & arr2 = text;//带长度的数组
  
   //c98语法
  	auto x1 = 27;
  	auto x2(27);
  //c11语法
  	auto x3={27};
  	auto x4{27};
   //c11 语法
  	auto x5={1,2,3};
    //error: deduced conflicting types ('int' vs 'double') for initializer list element typeauto x6={1,2,3.1};
	// auto x6={1,2,3.1};
  
  	f({1,2,3,4});
  //auto与模板推导的唯一区别：模板无法使用{}
  //f1({11});//error: use of undeclared identifier 'f1' f1({11});
  //f1({11,2});//error: use of undeclared identifier 'f1' f1({11,2});
}
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编译生成的代码如下：

#include <stdio.h>
#include <stdlib.h>
#include <iostream>

using namespace std;

void someFunc()
{
}

template<typename T>
void f0(T value){

}

template<typename T>
void f(std::initializer_list<T> value){

}

/* First instantiated from: insights.cpp:51 */
#ifdef INSIGHTS_USE_TEMPLATE
template<>
void f<int>(std::initializer_list<int> value)
{
}
#endif

int main()
{
  int x = 5;
  const int cx = x;
  const int & rx = x;
  const int * ptx = &x;
  int & rx1 = x;
  int * ptx1 = &x;
  int && uref1 = 5;
  int & uref2 = x;
  const int & uref3 = cx;
  const int & uref4 = rx;
  using FuncPtr_33 = void (*)();
  FuncPtr_33 func1 = someFunc;
  void (&func2)() = someFunc;
  const char text[14] = "xi men \345\220\271\351\233\252";
  const char * arr1 = text;
  char const (&arr2)[14] = text;
  int x1 = 27;
  int x2 = 27;
  std::initializer_list<int> x3 = std::initializer_list<int>{27};
  int x4 = {27};
  std::initializer_list<int> x5 = std::initializer_list<int>{1, 2, 3};
  f(std::initializer_list<int>{1, 2, 3, 4});
  return 0;
}
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