Print::printFloat erroneously prints 0.00 for large numbers.

What steps will reproduce the problem?

1. Execute this function call:   Serial.println(4294967290.0);

What is the expected output? What do you see instead?

I expect to see 4294967290.0 or similar (ie. rounded to 7 digits).

What I see is: 0.00

What version of the Arduino software are you using? On what operating
system?  Which Arduino board are you using?

IDE 1.0
OS/X
Uno

Please provide any additional information below.

It appears that the code below in Print::printFloat is responsible:

  // Extract the integer part of the number and print it
  unsigned long int_part = (unsigned long)number;

Because of imprecision in the storing of the floating point number, it is 
actually stored as 4.2949673e9 (4294967300) which is too large to fit into an 
unsigned long.

However surely printing 0.00 is very misleading? The number is certainly not 
zero.

Suggest either detecting this condition and printing "ovf" or similar, or 
amending the function printFloat to print the correct number.

It isn't much use providing a print for floats, which does not in fact handle 
large numbers.

Suggested fix:

if (number > 4294967040.0) return print ("ovf");  // constant determined 
empirically

Original issue reported on code.google.com by n...@gammon.com.au on 27 Jun 2012 at 5:16

code8825 / arduino

Print::printFloat erroneously prints 0.00 for large numbers. #967