to_string函数(c++11)

std::string to_string(int value);
std::string to_string(long value);
std::string to_string(long long value); 
std::string to_string(unsigned value); 
std::string to_string(unsigned long value);
std::string to_string(unsigned long long value);
std::string to_string(float value);
std::string to_string(double value);
std::string to_string(long double value);

用途：将数值转化为string