Assistance with String building

Projects Programming
1

Hi, new to Arduino and I'm working on a temperature sensor project that sends the temps to a web server.

I'm trying to build the "post" command with strings, but I'm finding that the Aduino is truncating the string and I'm not sure why. I know there complexities with the String command and I'm hoping someone can help.

Declared at beginning of program:

String OutputString;

Declared in setup:

OutputString = String("");

Declared in loop function:

    OutputString = String(OutputString + "temp01=" + dtostrf(temperatures[1], 3, 1, buffer));
    OutputString = String(OutputString + "&temp02=" + dtostrf(temperatures[2], 3, 1, buffer));
    OutputString = String(OutputString + "&temp03=" + dtostrf(temperatures[3], 3, 1, buffer));
    OutputString = String(OutputString + "&temp04=" + dtostrf(temperatures[4], 3, 1, buffer));
    OutputString = String(OutputString + "&temp05=" + dtostrf(temperatures[5], 3, 1, buffer));
    OutputString = String(OutputString + "&temp06=" + dtostrf(temperatures[6], 3, 1, buffer));
    OutputString = String(OutputString + "&temp07=" + dtostrf(temperatures[7], 3, 1, buffer));
    OutputString = String(OutputString + "&temp08=" + dtostrf(temperatures[8], 3, 1, buffer));

After the 5th assignment the string reverts back empty and starts over. I'm not sure if I'm hitting some sort of string length limit or something else. I tired changing the order of the output just in case something in the variable was causing the problem but the issue remained in the same place.

What am I missing? Thanks.

2

You're missing posting your code.

3

Holy cow - how many String objects are being created and discarded there? HOW fragmented will your heap be?!?!

Stop using String objects immediately. Do it with a character array and a snprintf() function call.

4

This is what the Examples teach.
They were written by PC coders who didn't understand what the RAM limits of AVR's mean.

You can find loads of tutorials on C strings, and books (used books cost less) with a chapter on them as well.
Here's one that I don't find objection to so far except there's not enough, it's just a beginning:

Here's the standard <string.h> library that Arduino uses, you have to #include <string.h> to get these:
http://www.nongnu.org/avr-libc/user-manual/group__avr__string.html

C strings do not copy themselves and erase the old one, unlike Strings.
C strings use less bytes, Strings have extra bytes needed.
C strings DO require the code to not write past the end of the array they are put/worked on inside.