1.explicit关键字
explicit关键字只需用于类内的单参数构造函数前面。由于无参数的构造函数和多参数的构造函数总是显示调用，这种情况在构造函数前加explicit无意义。google的c++规范中提到explicit的优点是可以避免不合时宜的类型变换，缺点无。所以google约定所有单参数的构造函数都必须是显示的，只有极少数情况下拷贝构造函数可以不声明称explicit。例如作为其他类的透明包装器的类。
effective c++中说：被声明为explicit的构造函数通常比其non-explicit兄弟更受欢迎。因为它们禁止编译器执行非预期（往往也不被期望）的类型转换。除非我有一个好理由允许构造函数被用于隐式类型转换，否则我会把它声明为explicit，鼓励大家遵循相同的政策。链接：https://www.cnblogs.com/rednodel/p/9299251.html
２.std::move()
std::move函数可以以非常简单的方式将左值引用转换为右值引用。
（左值、左值引用、右值、右值引用 参见：http://www.cnblogs.com/SZxiaochun/p/8017475.html）
通过std::move，可以避免不必要的拷贝操作。
std::move是为性能而生。
std::move是将对象的状态或者所有权从一个对象转移到另一个对象，只是转移，没有内存的搬迁或者内存拷贝。
#include <iostream> #include <utility> #include <vector> #include <string> int main() { std::string str = "Hello"; std::vector<std::string> v; //调用常规的拷贝构造函数，新建字符数组，拷贝数据 v.push_back(str); std::cout << "After copy, str is \"" << str << "\"\n"; //调用移动构造函数，掏空str，掏空后，最好不要使用str v.push_back(std::move(str)); std::cout << "After move, str is \"" << str << "\"\n"; std::cout << "The contents of the vector are \"" << v[0] << "\", \"" << v[1] << "\"\n"; }
３. std::numeric_limits
- 在C/C++11中，std::numeric_limits为模板类，在库编译平台提供基础算术类型的极值等属性信息，取代传统C语言，所采用的预处理常数。比较常用的使用是对于给定的基础类型用来判断在当前系统上的最大值、最小值。
- <limits>:头文件
- 原型：
template <class T> numeric_limits;
- 测试：
#include "numeric_limits.hpp" #include <limits> #include <iostream> ////////////////////////////////////////////////////////////////////// /* reference: http://www.cplusplus.com/reference/limits/numeric_limits/ https://msdn.microsoft.com/en-us/library/c707ct0t.aspx */ int test_numeric_limits_1() { std::cout << std::boolalpha; std::cout << "Minimum value for int: " << std::numeric_limits<int>::min() << std::endl; std::cout << "Maximum value for int: " << std::numeric_limits<int>::max() << std::endl; std::cout << "int is signed: " << std::numeric_limits<int>::is_signed << std::endl; std::cout << "Non-sign bits in int: " << std::numeric_limits<int>::digits << std::endl; std::cout << "int has infinity: " << std::numeric_limits<int>::has_infinity << std::endl; std::cout << "Minimum value for float: " << std::numeric_limits<float>::min() << std::endl; // min returns the smallest positive value the type can encode, not the lowest std::cout << "Lowest value for float: " << std::numeric_limits<float>::lowest() << std::endl; // the lowest value std::cout << "Maximum value for float: " << std::numeric_limits<float>::max() << std::endl; std::cout << "float is signed: " << std::numeric_limits<float>::is_signed << std::endl; std::cout << "Non-sign bits in float: " << std::numeric_limits<float>::digits << std::endl; std::cout << "float has infinity: " << std::numeric_limits<float>::has_infinity << std::endl; std::cout << "Minimum value for unsigned short: " << std::numeric_limits<unsigned short>::min() << std::endl; std::cout << "Maximum value for unsigned short: " << std::numeric_limits<unsigned short>::max() << std::endl; std::cout << "is_specialized(float): " << std::numeric_limits<float>::is_specialized << std::endl; std::cout << "is_integer(float): " << std::numeric_limits<float>::is_integer << std::endl; std::cout << "is_exact(float): " << std::numeric_limits<float>::is_exact << std::endl; std::cout << "is_bounded(float): " << std::numeric_limits<float>::is_bounded << std::endl; std::cout << "is_modulo(float): " << std::numeric_limits<float>::is_modulo << std::endl; std::cout << "is_iec559(float): " << std::numeric_limits<float>::is_iec559 << std::endl; std::cout << "digits10(float): " << std::numeric_limits<float>::digits10 << std::endl; std::cout << "radix(float): " << std::numeric_limits<float>::radix << std::endl; std::cout << "min_exponent(float): " << std::numeric_limits<float>::min_exponent << std::endl; std::cout << "max_exponent(float): " << std::numeric_limits<float>::max_exponent << std::endl; std::cout << "min_exponent10(float): " << std::numeric_limits<float>::min_exponent10 << std::endl; std::cout << "max_exponent10(float): " << std::numeric_limits<float>::max_exponent10 << std::endl; std::cout << "epsilon(float): " << std::numeric_limits<float>::epsilon() << std::endl; std::cout << "round_style(float): " << std::numeric_limits<float>::round_style << std::endl; std::cout << "The smallest nonzero denormalized value for float: " << std::numeric_limits<float>::denorm_min()<< std::endl; std::cout << "The difference between 1 and the smallest value greater than 1 for float: " << std::numeric_limits<float>::epsilon()<< std::endl; std::cout << "Whether float objects allow denormalized values: " << std::numeric_limits<float>::has_denorm << std::endl; std::cout << "Whether float objects can detect denormalized loss: " << std::numeric_limits<float>::has_denorm_loss << std::endl; std::cout << "Whether float objects have quiet_NaN: " << std::numeric_limits<float>::has_quiet_NaN << std::endl; std::cout << "Whether float objects have a signaling_NaN: " << std::numeric_limits<float>::has_signaling_NaN << std::endl; std::cout << "The base for type float is: " << std::numeric_limits<float>::radix << std::endl; std::cout << "The maximum rounding error for type float is: " << std::numeric_limits<float>::round_error() << std::endl; std::cout << "The rounding style for a double type is: " << std::numeric_limits<double>::round_style << std::endl; std::cout << "The signaling NaN for type float is: " << std::numeric_limits<float>::signaling_NaN() << std::endl; std::cout << "Whether float types can detect tinyness before rounding: " << std::numeric_limits<float>::tinyness_before << std::endl; std::cout << "Whether float types have implemented trapping: " << std::numeric_limits<float>::traps << std::endl; return 0; }
参考链接：https://blog.csdn.net/fengbingchun/article/details/77922558
