函数————to_string（将数字转换成字符串）
一般常用的转换字符串的方法std::stringstream,但是效率较低;目前C ++11提供了std::to_string
效率方面:C风格的sprintf()没有动态分配内存效率最高;std::to_string其次;std::stringstream效率最差
从C++17开始,std::to_string的效率将不差于sprintf,同时有类型更安全的转换函数std::to_char。
函数重载原型：
l w string to_string(int val);
l w string to_string(long val);
l w string to_string(long long val);
l w string to_string(unsigned val);
l w string to_string(unsigned long val);
l w string to_string(unsigned long long val);
l w string to_string(float val);
l w string to_string(double val);
l w string to_string(long double val);
1 1.#include <iostream> 2 2.#include <string> // std::to_string 3 3.#include <sstream> // std::stringstream 4 4.int main() 5 5.{ 6 6. // old method 7 7. std::stringstream ss; 8 8. ss << 1.23; 9 9. std::string str = ss.str(); 10 10. std::cout << str << std::endl; 11 11. // new method 12 12. std::string pi = "pi is" + std::to_string(3.1415926); 13 13. std::string perfect = std::to_string(1 + 2 + 4 + 7 + 14) + "is a perfect number"; 14 14. std::cout << pi << std::endl; 15 15. std::cout << perfect << std::endl; 16 16. return 0; 17 17.}
1. #include <iostream>
2. #include <string> // std::to_string
3. #include <sstream> // std::stringstream
4. int main()
5. {
6. // old method
7. std::stringstream ss;
8. ss << 1.23;
9. std::string str = ss.str();
10. std::cout << str << std::endl;
11. // new method
12. std::string pi = "pi is" + std::to_string(3.1415926);
13. std::string perfect = std::to_string(1 + 2 + 4 + 7 + 14) + "is a perfect number";
14. std::cout << pi << std::endl;
15. std::cout << perfect << std::endl;
16. return 0;
17. }
