BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Serializing struct for TCP sending          BorlandTalk.com Forum Index -> C++ Builder (Internet Socket) View previous topic :: View next topic   Author Message Stefano Bonifazi Guest Posted: Tue May 15, 2007 11:10 pm    Post subject: Serializing struct for TCP sending Hi all! In short I would like to send whole structure instances by using TCP-IP.. for example through Indy TCPClient. The first and secure way is to serialize the members of a structure in a buffer and then send them with procedure WriteBuffer(const ABuffer; AByteCount: Longint; const AWriteNow: boolean); Anyway for simple structures for example: struct { char name[255]; int intnum; float fnum; } my_struct; it seems to work even something like that: WriteBuffer (&myStruct,sizeof(my_struct)); that means that in memory they are simply placed one right the other.. so on the other side I can receive the buffer by knowing that structure size, and cast the buffer to that struct pointer! My question is: does that work always on every compiler? May the procedure of sending that buffer to a program, running on a different OS, produce a different object on destination even by using the same struct type on the second program? Maybe my problem is silly,and the answer obvious, but I am not sure of what a compiler does exactly allocating data when I create structures or classes, and what happen to data when sent by Indy or TCP-IP. Thank U very much in advance, Stefano B. Back to top Bob Gonder Guest Posted: Wed May 16, 2007 12:00 am    Post subject: Re: Serializing struct for TCP sending Stefano Bonifazi wrote: Quote: My question is: does that work always on every compiler? Yes, but the results may not be what you want them to be. Quote: May the procedure of sending that buffer to a program, running on a different OS, produce a different object on destination even by using the same struct type on the second program? Yes. See Endian issues. See also alignment issues. Quote: Maybe my problem is silly,and the answer obvious, but I am not sure of what a compiler does exactly allocating data when I create structures Depends on the alignment setting. The default is probably for your char name[255] to be 256 bytes of storage Most compilers align the internal items for fast processor access. So, a compiler for 8086 might default to byte-alignment while one for pentium would be 4 byte align, and perhaps one for mainframe would be 64 or even 128 bit aligned. This alignment is overridable by the programmer. Quote: and what happen to data when sent by Indy or TCP-IP. It is sent as-is. Bottom line: If you are sending exclusively to your own apps, you can do whatever you want (send raw structures). If you are sending to someone else's app, or your app that someone compiles for their harware, you might be better off converting integers and such into network-endian format and transmit the individual pieces. You might Google this group for endian http://tinyurl.com/28s62e Back to top Remy Lebeau (TeamB) Guest Posted: Wed May 16, 2007 12:02 am    Post subject: Re: Serializing struct for TCP sending "Bob Gonder" <notbg (AT) notmindspring (DOT) invalid> wrote in message news:hevj4394fkkbve5uiuicaf1614234a44j3 (AT) 4ax (DOT) com... Quote: If you are sending to someone else's app, or your app that someone compiles for their harware, you might be better off converting integers and such into network-endian format You should also use 1-byte alignment for your structures so that there is no unnecessary padding added by the compiler. Gambit Back to top Stefano Bonifazi Guest Posted: Wed May 16, 2007 12:54 am    Post subject: Re: Serializing struct for TCP sending Hi thank U very much to both! Quote: If you are sending to someone else's app, or your app that someone compiles for their harware, you might be better off converting integers and such into network-endian format sorry how? I always used Indy SendBuffer and on the other side even from Linux they receive fine! Quote: You should also use 1-byte alignment for your structures so that there is no unnecessary padding added by the compiler. U mean in "advanced compiler" options, "data alignment" right? Thank U again! Back to top Remy Lebeau (TeamB) Guest Posted: Wed May 16, 2007 1:33 am    Post subject: Re: Serializing struct for TCP sending "Stefano Bonifazi" <stefboombastic (AT) email (DOT) it> wrote in message news:464a101b (AT) newsgroups (DOT) borland.com... Quote: I always used Indy SendBuffer and on the other side even from Linux they receive fine! Windows and Linux run on the same hardware architecture, so the endian is the same. But if you were to exchange data with to a Mac or other non-PC machine, the endian would likely not match. Read/WriteBuffer() do not perform any endian conversions at all. Read/WriteInteger/Cardinal/SmallInt(), on the other hand, do perform conversions from/to network byte ordering by default. All systems understand network byte ordering, and the socket API provides functions (which Indy wraps internally) to convert numbers between network byte ordering (which is universal across networks) and host byte ordering (which is specific to the machine being run on). So, what you could do is send the individual members of your struct separately, ie: my_struct s; TCPClient->WriteBuffer(s.name, 255); TCPClient->WriteInteger(s.intnum); // and so on... TCPClient->ReadBuffer(s.name, 255); s.intnum = TCPClient->ReadInteger(); // and so on... Also, you might want to stay away from floating point numbers, if you can. The byte size and binary representation may work differently on different hardware architectures as well, regardless of the endian used. Quote: U mean in "advanced compiler" options, "data alignment" right? No. That is a global setting that effects the entire application as a whole. That would be very dangerous and error-prone. What you should do instead is wrap your individual structs with #pragma pack statements instead, ie: #pragma pack(push, 1) struct my_struct { //... }; #pragma pack(pop) Or: #include <pshpack1.h> struct my_struct { //... }; #include <poppack.h> Gambit Back to top Bob Gonder Guest Posted: Wed May 16, 2007 1:42 am    Post subject: Re: Serializing struct for TCP sending Stefano Bonifazi wrote: Quote: converting integers and such into network-endian format sorry how? See the link in my first message Back to top Stefano Bonifazi Guest Posted: Wed May 16, 2007 2:02 am    Post subject: Re: Serializing struct for TCP sending Hi Thank U very much! Remy Lebeau (TeamB) ha scritto: Quote: my_struct s; TCPClient->WriteBuffer(s.name, 255); TCPClient->WriteInteger(s.intnum); // and so on... what I exactly did always :) Quote: TCPClient->ReadBuffer(s.name, 255); s.intnum = TCPClient->ReadInteger(); // and so on... Wish they used Indy on Linux..they uses simple Liux socket API.. hope they perform conversion from Network endian to Host machine endian as well as!! Quote: Also, you might want to stay away from floating point numbers, if you can. The byte size and binary representation may work differently on different hardware architectures as well, regardless of the endian used. Engineering numbers are very seldom integers! .. So what to do? Quote: U mean in "advanced compiler" options, "data alignment" right? No. That is a global setting that effects the entire application as a whole. That would be very dangerous and error-prone. Oh really?? I wonder why they put the option if that is dangerous! Thank U!! What you should Quote: do instead is wrap your individual structs with #pragma pack statements instead, ie: #pragma pack(push, 1) struct my_struct { //... }; #pragma pack(pop) Or: #include <pshpack1.h struct my_struct { //... }; #include <poppack.h Thank U.. never heard about those before! My best regards! Stefano B. Back to top Stefano Bonifazi Guest Posted: Wed May 16, 2007 2:03 am    Post subject: Re: Serializing struct for TCP sending Bob Gonder wrote: Quote: See the link in my first message Thank U again! Back to top Remy Lebeau (TeamB) Guest Posted: Wed May 16, 2007 4:02 am    Post subject: Re: Serializing struct for TCP sending "Stefano Bonifazi" <stefboombastic (AT) email (DOT) it> wrote in message news:464a200d (AT) newsgroups (DOT) borland.com... Quote: Wish they used Indy on Linux..they uses simple Liux socket API.. Indy works on Linux, and is built on top of the same API. Quote: hope they perform conversion from Network endian to Host machine endian as well as!! Everybody does. It is the only way to ensure proper data integrity over a network across different platforms. Gambit Back to top Stefano Bonifazi Guest Posted: Wed May 16, 2007 4:26 pm    Post subject: Re: Serializing struct for TCP sending Hi Mr. Lebeau! Thank U for Ur answer! Quote: Wish they used Indy on Linux..they uses simple Liux socket API.. Indy works on Linux, and is built on top of the same API. Sure, sorry my english:( I meant I wished they(the programmers on Linux I am working with) would use Indy, but they don't, even though after my recommendation! :( Quote: hope they perform conversion from Network endian to Host machine endian as well as!! Everybody does. It is the only way to ensure proper data integrity over a network across different platforms. I c.. that's why that works even though I never did anything special to take care of it before :) Please have U suggestiond about sending floating point numbers? I can't do without! Should I convert them to string representation and send the strings instead to be sure nothing odd happens? Thank U again! Stefano B. 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