cppinsight对一些语言特性的解释

Posted 2023-03-08 奇妙之二进制

range based for loop循环

#include <cstdio>

int main()

    const char arr[]2,4,6,8,10;

    for(const char& c : arr)
    
      printf("c=%c\\n", c);
    

#include <cstdio>

int main()

  const char arr[5] = 2, 4, 6, 8, 10;
  
    const char (&__range1)[5] = arr;
    const char * __begin1 = __range1;
    const char * __end1 = __range1 + 5L;
    for(; __begin1 != __end1; ++__begin1) 
      const char & c = *__begin1;
      printf("c=%c\\n", static_cast<int>(c));
    
    
  
  return 0;

花括号初始化

int main()

  // The compiler automatically fills the remaining
  // fields with 0 thanks to braced initialization.
  int arr[5]2,3,4;

int main()

  int arr[5] = 2, 3, 4, 0, 0;
  return 0;

struct A 

  // user provided constructor _missing_ initialzation of `j`
  A()
  : i3
  
  
  int i;
  int j;
;

struct B

  // uses the default constructor
  int i;
  int j;
;

int main()

  A a;
  A a2; // only i gets initialized.
  
  B b;
  B b2;  // both i and j get initialized.

struct A

  inline A()
  : i3
  
  
  
  int i;
  int j;
;



struct B

  int i;
  int j;
  // inline B() noexcept = default;
;



int main()

  A a = A();
  A a2 = A;
  B b = B();
  B b2 = 0, 0;
  return 0;

auto推导

int main()

  auto i = 3;       // int
  auto a = 42;    // initializer list
  auto b42;       // int
  auto c = 1, 2;  // initializer list

#include <initializer_list>

int main()

  int i = 3;
  std::initializer_list<int> a = std::initializer_list<int>42;
  int b = 42;
  std::initializer_list<int> c = std::initializer_list<int>1, 2;
  return 0;

lamba表达式

int main()

  int (*fp)(int, char) = [](int a, char b) return a+b;;

int main()

      
  class __lambda_3_26
  
    public: 
    inline /*constexpr */ int operator()(int a, char b) const
    
      return a + static_cast<int>(b);
    
    
    using retType_3_26 = int (*)(int, char);
    inline constexpr operator retType_3_26 () const noexcept
    
      return __invoke;
    
    
    private: 
    static inline /*constexpr */ int __invoke(int a, char b)
    
      return __lambda_3_26.operator()(a, b);
    
    
    
  ;
  
  using FuncPtr_3 = int (*)(int, char);
  FuncPtr_3 fp = static_cast<int (*)(int, char)>(__lambda_3_26.operator __lambda_3_26::retType_3_26());
  return 0;

这个非常有意思，一个lamba表达式其实是一个类，它实现了函数调用运算符()重载，以及类型转换函数。

C++14的通用lamba

int main()

  // Generic lambdas have a method template call operator.
  auto x = [](auto x)  return x * x; ;
  
  x(2);   // int
  x(3.0); // double

int main()

    
  class __lambda_4_12
  
    public: 
    template<class type_parameter_0_0>
    inline /*constexpr */ auto operator()(type_parameter_0_0 x) const
    
      return x * x;
    
    
    #ifdef INSIGHTS_USE_TEMPLATE
    template<>
    inline /*constexpr */ int operator()<int>(int x) const
    
      return x * x;
    
    #endif
    
    
    #ifdef INSIGHTS_USE_TEMPLATE
    template<>
    inline /*constexpr */ double operator()<double>(double x) const
    
      return x * x;
    
    #endif
    
    private: 
    template<class type_parameter_0_0>
    static inline /*constexpr */ auto __invoke(type_parameter_0_0 x)
    
      return __lambda_4_12.operator()<type_parameter_0_0>(x);
    
    
  ;
  
  __lambda_4_12 x = __lambda_4_12;
  x.operator()(2);
  x.operator()(3.0);
  return 0;

int x = 1;
auto Bar() -> decltype(x)

  int x = 22;
  // do some fancy calculation with x
  return (x);

int x = 1;

int Bar()

  int x = 22;
  return (x);

lamba值捕获原理

class A 
;

int main()

    A a;
	auto f = [a](int i) return i;;

class A

  public: 
  // inline constexpr A() noexcept = default;
  // inline constexpr A(const A &) noexcept = default;
;



int main()

  A a = A();
    
  class __lambda_7_11
  
    public: 
    inline /*constexpr */ int operator()(int i) const
    
      return i;
    
    
    private: 
    A a;
    
    public:
    __lambda_7_11(const A & _a)
    : a_a
    
    
  ;
  
  __lambda_7_11 f = __lambda_7_11a;
  return 0;

引用捕获原理

class A 
;

int main()

    A a;
	auto f = [&a](int i) return i;;

class A

  public: 
  // inline constexpr A() noexcept = default;
;



int main()

  A a = A();
    
  class __lambda_7_11
  
    public: 
    inline /*constexpr */ int operator()(int i) const
    
      return i;
    
    
    private: 
    A & a;
    
    public:
    __lambda_7_11(A & _a)
    : a_a
    
    
  ;
  
  __lambda_7_11 f = __lambda_7_11a;
  return 0;

this捕获原理

class A 
  void fun() 
  	auto f = [this](int i) return i;;
  
;

int main()

    A a;

class A

  inline void fun()
  
        
    class __lambda_3_12
    
      public: 
      inline /*constexpr */ int operator()(int i) const
      
        return i;
      
      
      private: 
      A * __this;
      
      public:
      __lambda_3_12(A * _this)
      : __this_this
      
      
    ;
    
    __lambda_3_12 f = __lambda_3_12this;
  
  
  public: 
  // inline constexpr A() noexcept = default;
;


int main()

  A a = A();
  return 0;