- Template/STL question - help please - 5 Updates
| dakupoto@gmail.com: Sep 28 11:19PM -0700 Could some C++ guru please help ? May be my question is stupid, so pardon me. Can STL have a built-in method to handle ANY user defined data type ? To be specific, suppose I want to model a TCP/IP packet as a struct. As the memebers of a TCP/IP packet are in reality are byte arrays, I can visualize the entire packet as a large(1500) array of bytes, with the first so many bytes making up the source address and so on. So, I can use a vector of bytes to model a TCP/IP packet. But now the question is, can I just go ahead and use the struct as template type(like for example a built-in type as float, int etc.,) instead of first taking out the contents of the same TCP/IP packet and putting them into a byte vector ? Any hints/suggestions would be greatly appreciated -thanks in advance for your help. |
| Jorgen Grahn <grahn+nntp@snipabacken.se>: Sep 29 07:30AM > my question is stupid, so pardon me. > Can STL have a built-in method to handle > ANY user defined data type ? I don't understand that. > packet are in reality are byte arrays, > I can visualize the entire packet as a > large(1500) It can be larger than that, and if you reassemble fragments so you're looking at IP /datagrams/ rather than /packets/, it can reach 65535 octets. > so many bytes making up the source address > and so on. So, I can use a vector of bytes > to model a TCP/IP packet. Yes, that seems like a fair way to start. > of first taking out the contents of the same > TCP/IP packet and putting them into a byte > vector ? I don't understand what you're trying to say here. Which struct, and what do you mean by a "template type"? Please explain better. It seems like it could be an interesting question, once I understand it! If you mean this: std::vector<uint8_t> packet = something(); const struct ip_hdr* hdr = (struct ip_hdr*)&packet[0]; then I personally recommend against it. I always implement it as functions which read octet by octet from the buffer: struct in_addr src = src_of(packet); That avoids endianness and alignment bugs, and forces you to consider damaged packets and fragments. > Any hints/suggestions would be greatly > appreciated -thanks in advance for your help. /Jorgen -- // Jorgen Grahn <grahn@ Oo o. . . \X/ snipabacken.se> O o . |
| Robert Wessel <robertwessel2@yahoo.com>: Sep 29 03:19AM -0500 On 29 Sep 2015 07:30:41 GMT, Jorgen Grahn <grahn+nntp@snipabacken.se> wrote: >It can be larger than that, and if you reassemble fragments >so you're looking at IP /datagrams/ rather than /packets/, >it can reach 65535 octets. IPv6 jumbograms can be 4GiB. |
| Juha Nieminen <nospam@thanks.invalid>: Sep 29 08:24AM > But now the > question is, can I just go ahead and use > the struct as template type Why would you think you can't use a struct as a template type? --- news://freenews.netfront.net/ - complaints: news@netfront.net --- |
| scott@slp53.sl.home (Scott Lurndal): Sep 29 01:33PM >of first taking out the contents of the same >TCP/IP packet and putting them into a byte >vector ? namespace net { /** * Layer 2 (Ethernet) Header */ struct s_ethernet { uint8_t e_dest_mac[6]; uint8_t e_source_mac[6]; uint16_t e_ethertype; uint16_t get_ethertype(void) { return be16toh(e_ethertype); } } PACKED; /** * Layer 2 (Ethernet) Header with 802.1Q VLAN tag. */ struct s_802_1q_ethernet { uint8_t e_dest_mac[6]; uint8_t e_source_mac[6]; uint32_t e_802_1q_tag; uint16_t e_ethertype; uint16_t get_ethertype(void) { return be16toh(e_ethertype); } } PACKED; /** * Layer 3 IPv4 Header */ struct s_ipv4 { #if __BYTE_ORDER == __BIG_ENDIAN uint8_t i_version:4, i_ihl:4; #else uint8_t i_ihl:4, i_version:4; 
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