STL string大小写 转换

        std::string data = "This is a sample string.";
 
    // convert string to upper case
    std::for_each(data.begin(), data.end(), [](char & c) {
        c = ::toupper(c);
    });
 
    std::cout << "In Upper Case : " << data << std::endl;
 
    // convert string to back to lower case
    std::for_each(data.begin(), data.end(), [](char & c) {
        c = ::tolower(c);
    });
 
    std::cout << "In Lower Case : " << data << std::endl;