Thanks everyone for the extremely rapid help!

I tried both the 2-dimentional array and the strcpy() and they both achieve what I need.
I was just confusing myself with & (reference) and * (dereference) of pointers and getting nowhere.
The reason for the strange initialization values was just so I could see if what I was printing for diagnostics was what I thought it was. They are fixed length ascii temperatures that arrive by RS485 for storage and web-page viewing and logging.
I just start them off at zero rather than have nothing in them.
I'll opt for the 2-dimentional array and see how it all goes
Thanks again....
Stewie

Hi..

If I define an array of fixed length text items like...

char* temps[] = {" 000.00"," 000.01"," 000.02"," 000.03"," 000.04"," 000.05"," 000.06"," 000.07"," 000.08"," 000.09",};  // ascii string of temperature

I can display one of the entries by...
Serial.print (temps[3]);
which shows  000.03 as I'd expect.

as stuff happens in my program I try and update an entry
ie elsewhere I have a string of the correct length called 'temptemp', this hold different values on each pass of a loop

How do I change the contents one of the items in the 'temps' array to the new value?

If I do temps[3]=temptemp , then temps[1]=temptemp next time round, all the values I try and display always show the same (latest) value.
I suspect I'm just changing the pointers to the latest value but how do I modify the actual data?

I have read stuff about strings and pointers but cant figure out how to apply it to this case 
Any help would be welcome..

Yes, you are right about no (in the W5100 anyway) receive timeout. I dont understand the Ethernet library enough to know if it is in the software or not.
I was getting mixed up with the connect/transmit timeout. I implemented a receive timer in my assembly language version for just that reason or, as you say, you never get out of the loop.
I kept a stack of testing logs when I was working on the client side so I just had a look through them and right enough, the receive timeout error crops up several (2~5) times daily for Thingspeak. It tends to happen around the same period as 502 gateway unavailable conditions, also a daily occurrence. I put it down to server loading during busy periods, where it could not keep up (?)
The other errors that repeatedly come up are...
While waiting from a response to the connect request, a close arrives from the remote end, or...
Connection request simply times out.
At least both of these are simple to deal with, but as you pointed out, the receive side can just hang forever. I suspect that will be the source of at least one of my problems so thanks for highlighting that one.

The timeouts/bad-gateway errors seem to not happen for ages then a block of them appear off and on for perhaps 20min, then all back to plain sailing again. Its quite possible that sometimes the Arduino would get 'stuck'  at this point, but also possible for it to get lucky and sail through and not get caught till another time.

I'll try with the timeouts in place and see how it goes.

[timeout]

I thought that the read-from-client part that you have inside your timeout section should not be able to happen (in theory...)
The Ethernet library has a timeout and retries built into it and if the connection hangs while waiting for data then shouldn't the library force-close the socket? thus allowing exit from the wait/read loop?
Perhaps this force-close fails if a flush is not done first? or is it?
I'm just speculating here as I don't understand the internals of the library, which is what prompted me to do it in assembly.
I'd still rather understand whats happening in the high-level code 

Do you know if its possible to read the W5100 socket status register?

That would certainly help me with trying to pinpoint where things are going wrong, or at least perhaps rule some things out.

Its static IP
Also, In my attempt to reduce the potential of memory leaks/allocation problems I made almost everything global scope variables/arrays while monitoring free memory to see if it was getting eaten up by something. Bad practice from what I understand but if it nails everything down and removes a possibility then I can live with it for now. Currently 4473 bytes free.
Strings in Flash, static IP addresses except for a NTP access on boot and every 24hrs.

 - I just noticed that your timeout code just did its thing on a Nimbits post  . I'm watching the status as I tinker...

Hi Nick,
No, it wont on its own. In my original post I said..

"I include the logging code here so perhaps someone may spot something I'm doing wrong. It is only a section of the complete code".

I was hoping that someone may spot an obvious error in the section of code that does the POST.

The complete code is spread through five modules and is fairly large now.
One for the server and temperature retrieval, one for power switching, one each for Thingspeak & Nimbits and one for NTP

Thanks Tim,
I have incorporated your timeout into my code and will see if it makes a difference.
To date, about 3.5 days of uptime is my best. I'll be interested to see if this now changes (my fingers are crossed....)
Stewie

Hi book_woorm,
I have never been able to find a definitive answer but I have noticed that the length of time before lockup/crashes is maximised by not using DNS lookups so I use hard coded IP addresses.
Its not good as a long term fix but it makes a crash rate of hours turn into days.
The only section I still use a lookup is once every 24hrs I do a lookup for a timeserver at oceania.pool.ntp.org. If my home router had a timeserver function I could even hard-code that IP addr as well.
I have read many theories about the reasons for this, lack of memory often seems to come up as a possibilty. (have you seen the Goldilocks board?, 16K ram!)
To get around my lockups, I use the watchdog timer to reboot the board. It always seems to come back up OK.
On my Arduino server, I have an uptime timer (days/hrs/min/sec) so when I look at the page I know how long its been since its last reset.
What I dont differentiate (yet) is whether a reboot is due to an ethernet lockup or a string of five consecutive logging-service post failures. I will remedy that soon.
It seems that the logging sites can miss quite a few posts in busy times, at least thingspeak can, nimbits seems more reliable in that sense.
This is only my personal experiences.
One thing you are doing that i dont is writing to the SD card. I just read from one. I'm not sure if writing uses more ram.
Good luck with your coding, I hope you find some answers
Stewie

Thanks for your input
I have tweaked and adjusted and tried many things but the end result is the same which is after one or two days, it locks-up.
To keep things happening, the watchdog reboots the board and it all seems happy again. Its transparent to the user, the only way I know its happened is an uptime timer on the web-page.
Perhaps I'm just trying to do too much on the one board..
NTP lookup, web-server for control/status and client for posting logging data.
I just dont understand C or C++ well enough to dig deep down. In time perhaps.....
Meantime, I have written a server and client for the wiznet in assembly language. Its a fraction of the size, but not as comprehensive. DNS and NTP still to do....
Driving the W5100 at register level has been quite educational. I certainly learned a lot about the structure of web transactions.
With the low-level access, its easier to see whats going wrong. This highlights the lack of useful diagnostic and status info that is 'missing' from the ethernet library, which is basically a go/no-go affair but nothing available to show whats going on in the background, or at what point something failed.

Now that I know a lot more about the chip, I can have another try at the C-code and see if it makes more sense.

Hi all,
An outline of what I have is....
An RF network of RFM12 nodes with 1-wire temp sensors and an RFM12-enabled 4 output mains power switch (for lights or whatever) . These communicate to a 'gateway' that collects the info from all the RF nodes and deals with command/responses for the power-switch box.
The gateway links to an Ethermega by RS485.

On the Ethermega, I run a webserver that displays some of the temperatures and lets you turn on/off the 4 power outputs.
Also on the  Ethermega, a client logs the temperatures to both nimbits and thingspeak (every 60-sec for Thingspeak, 90-sec for nimbits).
On startup, the time is retrieved from a NTP timeserver and each midnight thereafter.

What I notice is that when using the client connect with a name lookup, ie cloud.nimbits.com, NOT a fixed IP, the client side of the Ethermega eventually hangs up. This can take  up to 6-hrs or even after 20-min , but the server side continues to work when the client side stops.

I am currently trying the client side (logging) with fixed IP addresses (which is not a long term solution) and at the same time the ethermega server is being worked by having a autorefresh request from firefox every 10 sec.
Since moving to fixed IP addresses for the logging, the system has been stable for 24 hours (longest ever!) now of logging to two sites and serving up a webpage every 10 seconds without a hitch ( over 8600 page refreshes).

While trying to investigate this I came across a Wiznet errata document (W3150A+/W5100 Errata Sheet) on the W5100 chip about possible errors relating to ARP requests but I am a very inexperienced at C and I lack the understanding to figure out if the fix for the errata has been included in the ethernet library, or even if the client failure while using lookups could be caused by this so I'm hoping for someone with better C/C++ understanding who has looked into this and may be willing to share their experiences and understanding.

I include the logging code here so perhaps someone may spot something I'm doing wrong. It is only a section of the complete code.

When the client side accumulates 5 successive failures, the whole system is reset by the WDT. I have never had a problem with the ethernet not coming back after a reboot.

Is there any way to check how many W5100 sockets are currently available?

Any help/suggestions gratefully received 

Thanks.

Code:

/*
posts to nimbits

Uses the PString.h library.
Instead of making many connections to the server using the usual Arduino ethernet functions
like 'client.print' (every statement is a separate trasnaction), all the data to send in the
POST trasaction is 'assembled' into one large string using the Pstring library,
which then gets sent in one hit. This reduces the IP traffic considerably
*/



void do_weblog() {
    // if 'postinginterval' secs have passed since
    // your last connection, then connect again and send data:
    if((millis() - lastCloudTime > postingInterval)) {
        line();
        showTimeDate();
        showRunTime();
        sendData();    // the POST happens here
        delay(2);
        }
    }



// this makes a HTTP connection to the logging server:

void sendData() {

byte cloud[] = { 74, 125, 31, 121 }; // cloud.nimbits.com

        str.begin();    // reset the into-string pointer. This is the 'main' string being assembled.
        cont.begin();   // and for the actual content ie payload string

// Create the 'content' of the string to send. Its assembled from the user details, then the sensor data
// 1st part of content is access details
        cont.print("email=XXXXXXXXXXXXXXXX&key=YYYYYYYYYYYYYY");    // store in the string 'cont'

// the sensor data is aquired from the RFM12 gateway that receives all the assorted temp sensor data
// get the data and store it in the 'cont' string. Data is requested from the RFM12 'gateway' using RS485.
        cont.print("&p1=hot-water&v1=");
        GetTemperature(0);        // hot water address
        cont.print(temptemp);    //
        cont.print("&p2=outside1&v2=");
        GetTemperature(5);        // turning circle sensor adress
        cont.print(temptemp);    //
        cont.print("&p3=highest&v3=");
        GetTemperature(7);        // library sensor address
        cont.print(temptemp);    //
        cont.print("&p4=freezer1&v4=");
        GetTemperature(6);        // freezer in pantry address
        cont.print(temptemp);    //
        cont.print("&p5=workshop&v5=");
        GetTemperature(1);        // workshop address
        cont.print(temptemp);    //
       
 // now get the length of the assembled content string. This string is the complete 'content'
        int contlen = (cont.length());
       
 // Got the content assembled so try and connect to the web-site

    EthernetClient Logging_client;      // client for both logging services
    Serial2.println("Attempting to connect to Nimbits...");

    if (Logging_client.connect(cloud, 80))
//    if (Logging_client.connect("cloud.nimbits.com", 80))
    {
        str.println("POST /service/batch HTTP/1.1");
        str.println("Host: cloud.nimbits.com");
        str.println("Connection: close");
        str.println("Cache-Control: max-age=0");
        str.print("Content-Length: ");
        str.println(contlen,DEC);
        str.println("Content-Type: application/x-www-form-urlencoded");
        str.println();
        str.println(cont);    // the actual content (data points)

// the total string ('post' headers and content) is sent to the ethernet connection in one hit
        Logging_client.print(str);  // ethernet send to COSM

        Serial2.println();        // for debug
        Serial2.print(str);       // this is a copy of whats sent to the ethernet (same string)
        Serial2.println();        // for debug
        Serial2.println();        // for debug

      bufindex = 0;

// look for response
    while (Logging_client.connected()) {
      if (Logging_client.available()) {
        char c = Logging_client.read();
        Serial2.print(c);
        if (bufindex < 198) {
          //store characters to string
         content[bufindex] = c;
         bufindex = bufindex+1;
       }
      }
      content[bufindex] = 0;
     }

    if (strstr(content, "200 OK") != 0) {
       failcount = 0;    // reset after every successfull connect
   }
    else {
        // if you couldn't make a connection:
        failcount = failcount + 1;
         }   
    }
// The above is when the connection succeeds and data is sent/received   



// if the connection fails then here is next
    else {
        // if you couldn't make a connection:
        failcount = failcount + 1;
        Serial2.print("Connection failed ");
        }
 
 
// and after here for either good or bad connection
      Logging_client.flush();    // ensure no data left in buffer (wont allow close if present)
      Logging_client.stop();     // and finish the socket

      Serial2.print("failcount ");
      Serial2.println(failcount);

        if (failcount > 5) {    // if connection consistently failing then reboot.
          WDTreboot();        // sets up an 8-sec timeout
        }
 
    lastCloudTime = millis();
}

Hi,
This is probably a simple one when you know what your doing or can dig into the library code in the ethernet files but I am having difficulty in figuring out how to switch between my ethernet board being a server then switching to a client and back again.
I have an embedded application that allows me to switch lights on and off & display the temperature of my solar hot water system. The web side of it runs on an ethermega and as it serves my pages, embedded tokens get filled in by the real-world data (via RS485 & RFM12 links). This all works OK.
Now what I would like to do is from time-to-time, send some of the temperature data to Pachube but I cant figure out how to stop the board being a server and switch to a client to allow the Pachube stuff, then back to a server again.
Any help with this would be appreciated.
I am not a 'C' programmer but bit by painful bit I'm getting less worse. Usually I write embedded stuff in assembly but as Arduino seemed the way to go for the web-interface side, I'm slowly trying to get there....