Constantes pré-definidas

As constantes abaixo estão sempre disponíveis como parte do núcleo do PHP.

**Constantes matemáticas**
Constante	Valor	Descrição
`M_PI`	3.14159265358979323846	Pi
`M_E`	2.7182818284590452354	e - número neperiano
`M_LOG2E`	1.4426950408889634074	logaritmo de e na base 2
`M_LOG10E`	0.43429448190325182765	logaritmo de e na base 10
`M_LN2`	0.69314718055994530942	logaritmo neperiano de 2
`M_LN10`	2.30258509299404568402	logaritmo neperiano de 10
`M_PI_2`	1.57079632679489661923	pi/2
`M_PI_4`	0.78539816339744830962	pi/4
`M_1_PI`	0.31830988618379067154	1/pi
`M_2_PI`	0.63661977236758134308	2/pi
`M_SQRTPI`	1.77245385090551602729	raiz(pi)
`M_2_SQRTPI`	1.12837916709551257390	2/raiz(pi)
`M_SQRT2`	1.41421356237309504880	raiz(2)
`M_SQRT3`	1.73205080756887729352	raiz(3)
`M_SQRT1_2`	0.70710678118654752440	1/raiz(2)
`M_LNPI`	1.14472988584940017414	logaritmo neperiano de pi
`M_EULER`	0.57721566490153286061	Constante de Euler
`PHP_ROUND_HALF_UP`	1	Arredonda 0.5 para cima
`PHP_ROUND_HALF_DOWN`	2	Arredonte 0.5 para baixo
`PHP_ROUND_HALF_EVEN`	3	Arredonda 0.5 para números pares
`PHP_ROUND_HALF_ODD`	4	Arredonda 0.5 para números ímpares
`NAN`	NAN (como um float)	Not A Number - um não-número
`INF`	INF (como um float)	Infinito

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User Contributed Notes 7 notes

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md2perpe at gmail dot com ¶

9 years ago


I just learnt of INF today and found out that it can be used in comparisons:

    echo 5000 < INF ? 'yes' : 'no';       // outputs 'yes'
    echo INF < INF ? 'yes' : 'no';        // outputs 'no'
    echo INF <= INF ? 'yes' : 'no';       // outputs 'yes'
    echo INF == INF ? 'yes' : 'no';       // outputs 'yes'

You can also take its negative:

    echo -INF < -5000 ? 'yes' : 'no';    // outputs 'yes'

Division by INF is allowed:

    echo 1/INF;    // outputs '0'

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Hayley Watson ¶

12 years ago


There are also the predefined PHP_INT_MAX and PHP_INT_SIZE constants, that describe the range of possible integer values.

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pemapmodder1970 at gmail dot com ¶

8 years ago


Although INF can be used for comparison against normal numbers and as a directed number, and behaves as reciprocal of zero, it is not like limit INF tends to infinity. These operations do not work:

<?php
var_dump(INF / INF); // float(NAN)
var_dump(INF - INF); // float(NAN)
?>

However, it works with arc-tangent:
<?php
var_dump(atan(INF) / M_PI); // float(0.5)
var_dump(atan2(INF, INF) / M_PI); // float(0.25)
var_dump(atan2(1, INF) / M_PI); // float(0)
?>

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Hayley Watson ¶

7 years ago


From PHP 7.2.0, the PHP_FLOAT_* constants are provided to describe the properties of floating point numbers that can be stored; PHP_FLOAT_MAX, for example, is analogous to PHP_INT_MAX and represents the largest possible floating-point number.

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br at ndon dot co ¶

3 years ago


The constants 

PHP_ROUND_HALF_UP
PHP_ROUND_HALF_DOWN
PHP_ROUND_HALF_EVEN
PHP_ROUND_HALF_ODD

are constants intended to be used as the 3rd parameter in the math function round() 

https://www.php.net/manual/en/function.round

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steve at websmithery dot co dot uk ¶

7 years ago


Another observation on INF.

Division by zero results in INF:

<?php
var_dump(1/0); // float(INF)
?>

BUT a 'Division by zero' warning is issued.

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-2

Kira-Bianca dot Hinz at web dot de ¶

4 years ago


Caution when using variables with the value NAN (or directly NAN, which would not be logical) if the value is converted in any form (integer, string or other non-float format)!
In that case, NAN is converted to 0. (e.g. as an index in an array, argument of a method that takes it as a non-float parameter, etc.). This bug has been reported several times, but is still present in the current version PHP 7.3.15.

Example 1:
$array = [0 =>  'zero', 1 => 'one', 2 => 'two'];
$index = NAN;
echo $array[$index]; // echo 'zero' and not as axcepted throws an exception or at least a warning 'undefined offset NAN ...'

Example 2:
function f((int) $p) { return $p; }
echo f(NAN); // echo 0 because the argument (NAN) has been converted to integer (0)

It would have to be checked in both cases explicitly for is_nan():
1: if(is_nan($index)){
      <throw Exception>
   }else{
      echo $array[$index];
   };

2: function f($p){ // without converting!!!
      if(is_nan($p)){
         <throw Exception>
      }else{
         return (int)$p; // actually a correct conversion  to Integer would have to be checked because the parser does not check this here.
      };
   }

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