Send the Content-Type of the sent entity.
注意: This function is supposed to be used in conjunction with http_send_data(), http_send_file() 和 http_send_stream().
Raises an E_WARNING when the content_type
doesn't seem to contain a primary and a secondary part.
http_send_data() |
http_send_file() |
http_send_stream() |
the HttpResponse class if you are using PHP-5.1 and above |