C++ string與int的相互轉換(使用C++11)
一、int轉string
#include <iostream> #include <string> int main() { double f = 23.43; double f2 = 1e-9; double f3 = 1e40; double f4 = 1e-40; double f5 = 123456789; std::string f_str = std::to_string(f); std::string f_str2 = std::to_string(f2); // 註意:返回 "0.000000" std::string f_str3 = std::to_string(f3); // 註意:不返回 "1e+40". std::string f_str4 = std::to_string(f4); // 註意:返回 "0.000000" std::string f_str5 = std::to_string(f5); std::cout << "std::cout: " << f << '\n' << "to_string: " << f_str << "\n\n" << "std::cout: " << f2 << '\n' << "to_string: " << f_str2 << "\n\n" << "std::cout: " << f3 << '\n' << "to_string: " << f_str3 << "\n\n" << "std::cout: " << f4 << '\n' << "to_string: " << f_str4 << "\n\n" << "std::cout: " << f5 << '\n' << "to_string: " << f_str5 << '\n'; }
輸出
std::cout: 23.43
to_string: 23.430000
std::cout: 1e-09
to_string: 0.000000
std::cout: 1e+40
to_string: 10000000000000000303786028427003666890752.000000
std::cout: 1e-40
to_string: 0.000000
std::cout: 1.23457e+08
to_string: 123456789.000000
二、string轉int
#include <iostream> #include <string> int main() { std::string str1 = "45"; std::string str2 = "3.14159"; std::string str3 = "31337 with words"; std::string str4 = "words and 2"; int myint1 = std::stoi(str1); int myint2 = std::stoi(str2); int myint3 = std::stoi(str3); // 錯誤: 'std::invalid_argument' // int myint4 = std::stoi(str4); std::cout << "std::stoi(\"" << str1 << "\") is " << myint1 << '\n'; std::cout << "std::stoi(\"" << str2 << "\") is " << myint2 << '\n'; std::cout << "std::stoi(\"" << str3 << "\") is " << myint3 << '\n'; //std::cout << "std::stoi(\"" << str4 << "\") is " << myint4 << '\n'; }
結果:
std::stoi("45") is 45
std::stoi("3.14159") is 3
std::stoi("31337 with words") is 31337
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