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;