PHP: Predefined Constants - Manual (original) (raw)
The constants below are always available as part of the PHP core.
Mathematical Constants
[M_PI](math.constants.php#constant.m-pi) (float)
Approximation of the number π (pi). (3.14159265358979323846).
[M_E](math.constants.php#constant.m-e) (float)
Approximation of Euler's number e (2.7182818284590452354).
[M_LOG2E](math.constants.php#constant.m-log2e) (float)
Approximation of log2(e) (1.4426950408889634074).
[M_LOG10E](math.constants.php#constant.m-log10e) (float)
Approximation of log10(e) (0.43429448190325182765).
[M_LN2](math.constants.php#constant.m-ln2) (float)
Approximation of ln(2) (0.69314718055994530942).
[M_LN10](math.constants.php#constant.m-ln10) (float)
Approximation of ln(10) (2.30258509299404568402).
[M_PI_2](math.constants.php#constant.m-pi-2) (float)
Approximation of π/2 (1.57079632679489661923).
[M_PI_4](math.constants.php#constant.m-pi-4) (float)
Approximation of π/4 (0.78539816339744830962).
[M_1_PI](math.constants.php#constant.m-1-pi) (float)
Approximation of 1/π (0.31830988618379067154).
[M_2_PI](math.constants.php#constant.m-2-pi) (float)
Approximation of 2/π (0.63661977236758134308).
[M_SQRTPI](math.constants.php#constant.m-sqrtpi) (float)
Approximation of sqrt(π) (1.77245385090551602729).
[M_2_SQRTPI](math.constants.php#constant.m-2-sqrtpi) (float)
Approximation of 2/sqrt(π) (1.12837916709551257390).
[M_SQRT2](math.constants.php#constant.m-sqrt2) (float)
Approximation of sqrt(2) (1.41421356237309504880).
[M_SQRT3](math.constants.php#constant.m-sqrt3) (float)
Approximation of sqrt(3) (1.73205080756887729352).
[M_SQRT1_2](math.constants.php#constant.m-sqrt1-2) (float)
Approximation of 1/sqrt(2) (0.70710678118654752440).
[M_LNPI](math.constants.php#constant.m-lnpi) (float)
Approximation of ln(π) (1.14472988584940017414).
[M_EULER](math.constants.php#constant.m-euler) (float)
Approximation of Euler's constant γ (0.57721566490153286061).
IEEE 754 floating point constants
[NAN](math.constants.php#constant.nan) (float)
Not A Number
[INF](math.constants.php#constant.inf) (float)
Infinity
Rounding constants
Note: As of PHP 8.4.0, it is recommended to use the RoundingMode enum instead.
[PHP_ROUND_HALF_UP](math.constants.php#constant.php-round-half-up) (int)
Rounding half away from zero.
[PHP_ROUND_HALF_DOWN](math.constants.php#constant.php-round-half-down) (int)
Rounding half toward zero.
[PHP_ROUND_HALF_EVEN](math.constants.php#constant.php-round-half-even) (int)
Round halves to even numbers
[PHP_ROUND_HALF_ODD](math.constants.php#constant.php-round-half-odd) (int)
Round halves to odd numbers
Found A Problem?
10 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 '0'13 years ago
There are also the predefined PHP_INT_MAX and PHP_INT_SIZE constants, that describe the range of possible integer values.pemapmodder1970 at gmail dot com ¶
9 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)
?>8 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.