unsigned long: value vs calculation

[Tnuz]

I'm not sure if this is a bug, or I'm doing something wrong, but is sure is weird.
I'm using Arduino 1.0.5-r2.

const unsigned long var1 = 32000; // the value of var1 = 32000 const unsigned long var2 = 32_1000; // the value of var2 = 32000 const unsigned long var3 = 33000; // the value of var3 = 33000 const unsigned long var4 = 33_1000; // the value of var4 = 4294934760

[Coding-Badly]

It is something you are doing wrong. Ask for help on the forum.

[matthijskooijman]

The problem is that an integer literal will have type "int" (provided the literal fits in there). This means that "33000" will be "long" (or "unsigned int", not sure), but "33" and "1000" will be int. If you multiple int * int, you'll get int, so 33 * 1000 will overflow and become something around -32400. When converted to long, that becomes the big number you see (LONG_MAX - 32400).

To fix this, make sure you convert to long before multiplying, either by doing (unsigned long)33 * 1000, or simpler: 33UL * 1000UL.

[Tnuz]

Thanks. I got it. That explains it very well :)
I got into this by using the 'WebClientRepeating' example in the Ethernet library. Funny I couldn't find other reports from people that this didn't work for then.

[matthijskooijman]

Looks like the example was already fixed in the 1.5.x IDE version (not in 1.0), so that should sort itself out once 1.5.x becomes stable. Thanks for reporting back with extra info though, it would have helped if it wasn't fixed yet :-)

https://github.com/arduino/Arduino/blob/ide-1.5.x/libraries/Ethernet/examples/WebClientRepeating/WebClientRepeating.ino#L47
a21c4e1#diff-2fde662c688bbe854220db2e841cfbc6R42