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Re: [lwip-users] Sending out TCP-Data as integer type

From: Mark Lakata
Subject: Re: [lwip-users] Sending out TCP-Data as integer type
Date: Wed, 05 Dec 2012 13:37:49 -0800
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:16.0) Gecko/20121026 Thunderbird/16.0.2

Read up on integers and how they are stored in memory http://en.wikipedia.org/wiki/Endianness

Try this

int data = "">

tcp_write(pcb, data, 4, 1); // I changed the 1 to a 4


and see what you get in wireshark. You'll probably get

00 FF xx xx (where xx is don't care garbage since you have a big endian 16-bit architecture)


00 00 00 FF (since you have a 32 bit bit endian architecture)


On 12/5/2012 6:38 AM, Firedog I. wrote:

Hi everyone,


I got a little problem over here. I can send simple TCP-Data like string and char, but I can’t send data as integer type. I’m using lwIP v1.36 with RAW API.




/*Connection to Client established…*/

int data = "" //or int data = "">

tcp_write(pcb, data, 1, 1);



When sending this Packet out, I receive a “00” as data in Wireshark.


I’ve tried sending out the equal ASCII-char to 255, a “ÿ“ (see extended ASCII), and this one works. When sending out this char, Wireshark shows a TCP-Packet with 1 byte length and a "ff" as data. That’s exactly what I want, but I don’t want to convert integer vars into extended ascii and then send the converted data out.


Any suggestions how to solve the problem?


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