字符串中的TRIM操作

std::string& ltrim(std::string& str, const std::string& chars = "\t\n\v\f\r ");
std::string& rtrim(std::string& str, const std::string& chars = "\t\n\v\f\r ");
std::string& trim(std::string& str, const std::string& chars = "\t\n\v\f\r ");

std::string& ltrim(std::string& str, const std::string& chars)
{
    str.erase(, str.find_first_not_of(chars));
    return str;
}

std::string& rtrim(std::string& str, const std::string& chars)
{
    str.erase(str.find_last_not_of(chars) + );
    return str;
}

std::string& trim(std::string& str, const std::string& chars)
{
    return ltrim(rtrim(str, chars), chars);
}