Convert float to plain string representation

Question

SO,

The problem

My question is about trivial thing: how to convert numeric string to it\'s plain (\"native\") representation. That means: if

Answer 1

Because sprintf() with "%.f" has trouble with expressions such as "1e-8", some text processing may be required:

function convertFloat($floatAsString)
{
    $norm = strval(floatval($floatAsString));

    if (($e = strrchr($norm, 'E')) === false) {
        return $norm;
    }

    return number_format($norm, -intval(substr($e, 1)));
}

Tested with:

3          3
1.5        1.5
-15.482e-2 -0.15482
1e-8       0.00000001
1e+3       1000
-4.66E-2   -0.0466
3e-3       0.003

Answer 2

# convert output of used php-math functions like sin in scientific notation to decimal notation
function xpnd($scientific, $precision){ # expand from scientific notation
  if(is_int($scientific)){ #don't convert integers
    return $scientific; 
  }
  return sprintf("%.".$precision."F", $scientific);
}

Where $precision is the desired number of fractional digits.

Answer 3

(Updated to use non-depreciated functions as suggested by andufo; I chose explode, but you could use preg_split if you wanted. As a side note if anyone still reads down this far, the accepted answer fails - try it with my first and last test case.)

I dug up a little gem from the PHP boards posted by benjcarson in 2002 who noted your exact problem with bcmath and scientific notation

It needed some adjustment (his function didn't set the right scale, and failed on regular decimals, and as pointed out it did not account for the length of decimal places in the scale)

function exp2int($exp) {
  list($mantissa, $exponent) = explode("e", strtolower($exp));
  if($exponent=='') return $exp;
  list($int, $dec) = explode(".", $mantissa);
  bcscale (abs($exponent-strlen($dec)));
  return bcmul($mantissa, bcpow("10", $exponent));
}

As a side note, your original code fails on any numbers smaller than 1E-40

(As do all the current answers using sprintf)

It would have been easier to debug if you posted more of your test cases, but this works for everything you've posted so far

Test cases:

echo exp2int("-1.82235135978667123456789E5"); \\-182235.135978667123456789
echo exp2int("1.1350865232E-60"); \\0.0000000000000000000000000000000000000000000000000000000000011350865232
echo exp2int("-15.482E-2"); \\-0.15482
echo exp2int("1.5"); \\1.5
echo exp2int("3"); \\3
echo exp2int("123.123e10"); \\1231230000000.000 - you mentioned trailing 0's aren't a problem
echo exp2int("123.123e-10"); \\0.0000000123123
echo exp2int("123456789E-9"); \\0.123456789
echo exp2int("12345.6789E-5"); \\0.123456789
echo exp2int("1E-300"); \\0.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001

Answer 4

For those who just wants to convert float to string.

function float_to_string($float)
{
    $string = (string)$float;

    if (preg_match('~\.(\d+)E([+-])?(\d+)~', $string, $matches)) {
        $decimals = $matches[2] === '-' ? strlen($matches[1]) + $matches[3] : 0;
        $string = number_format($float, $decimals,'.','');
    }

    return $string;
}

$float = 0.00000000020001;

echo $float; // 2.0001E-10
echo PHP_EOL;
echo float_to_string($float); // 0.00000000020001
echo PHP_EOL;

$float = 10000000000000000000000;

echo $float; // 1.0E+22
echo PHP_EOL;
echo float_to_string($float); // 10000000000000000000000
echo PHP_EOL;