is_float()

(PHP 4, PHP 5, PHP 7)

检测变量是否是浮点型

描述

如果$var是float则返回TRUE，否则返回FALSE。

若想测试一个变量是否是数字或数字字符串（如表单输入，它们通常为字符串），必须使用is_numeric()。

参见is_bool()、is_int()、is_integer()、is_numeric()、is_string()、is_array()和is_object()。

Boylett's solution is elegant (http://php.net/manual/en/function.is-float.php#85848), but won't work for long float's or variables that are not explicitly type of 'string' or for long floats that are encased in quotes, making it a string that will be truncated/rounded when cast to a float. So, further logic must be completed to test for the case. Take the following example:

Will produce (32-bit):
string(34) "3.14159265358979323846264338g32795"
float(3.1415926535898)
bool(false)
bool(false)
So far, so good, right? Yeah, but it's misleading, because the string is so long, that when it's converted to a float, it won't be equivalent to the comparison of the value being cast back into a string . So the aforementioned short function works. Look at this next example:

Will produce (32-bit):
float(3.1415926535898)
float(3.1415926535898)
bool(false)
bool(true)
Why is it not working now, but the value is truly a float? Same reasoning as mentioned before. The float is so long that it's truncated/rounded and doesn't match the comparison being done with the short-hand function.
So, as you can see, more logic should be applied to the variable you're testing.

Coercing the value to float and back to string was a neat trick. You can also just add a literal 0 to whatever you're checking.

Seems to work ok:

YMMV

If you want to test whether a string is containing a float, rather than if a variable is a float, you can use this simple little function:
function isfloat($f) return ($f == (string)(float)$f);

As celelibi at gmail dot com stated, is_float checks ONLY the type of the variable not the data it holds!
If you want to check if string represent a floating point value use the following regular expression and not is_float(),
or poorly written custom functions.
/^[+-]?(([0-9]+)|([0-9]*\.[0-9]+|[0-9]+\.[0-9]*)|
(([0-9]+|([0-9]*\.[0-9]+|[0-9]+\.[0-9]*))[eE][+-]?[0-9]+))$/

Yet another regular expression for float in real life:

// Matches:
1, -1, 1.0, -1.0, '1', '-1', '1.0', '-1.0', '2.1', '0', 0, ' 0 ', ' 0.1 ', ' -0.0 ', -0.0, 3., '-3.', '.27', .27, '-0', '+4', '1e2', '+1353.0316547', '13213.032468e-13465', '-8E+3', '-1354.98879e+37436'
// Non-matches:
false, true, '', '-', '.a', '-1.a', '.a', '.', '-.', '1+', '1.3+', 'a1', 'e.e', '-e-4', 'e2', '8e', '3,25'

Another RegEx for matching floats:
/^[+-]?(\d*\.\d+([eE]?[+-]?\d+)?|\d+[eE][+-]?\d+)$/
Matches:
1e2
+1353.0316547
13213.032468e-13465
-8E+3
-1354.98879e+37436
Non-matches:
8
e2
-e-4
E
asdf.safd
8e
Enjoy.

A better way to check for a certain number of decimal places is to use :
$num_dec_places = 2;
number_format($value,$num_dec_places);

check if string/numeric is float or not : 

Personally, I use an implicit cast:
if( is_float($value+1) ){
  $value=sprintf("%.2f",$value);
}
Which turns 22.0000000 query result into 22.00 for display to users.

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