Предопределенные константы
Перечисленные ниже константы всегда доступны как часть ядра PHP.
| Константа | Значение | Описание |
|---|---|---|
| M_PI | 3.14159265358979323846 | число пи |
| M_E | 2.7182818284590452354 | число Эйлера |
| M_LOG2E | 1.4426950408889634074 | log_2 e |
| M_LOG10E | 0.43429448190325182765 | lg e |
| M_LN2 | 0.69314718055994530942 | ln 2 |
| M_LN10 | 2.30258509299404568402 | ln 10 |
| M_PI_2 | 1.57079632679489661923 | пи/2 |
| M_PI_4 | 0.78539816339744830962 | пи/4 |
| M_1_PI | 0.31830988618379067154 | 1/пи |
| M_2_PI | 0.63661977236758134308 | 2/пи |
| M_SQRTPI | 1.77245385090551602729 | sqrt(пи) [4.0.2] |
| M_2_SQRTPI | 1.12837916709551257390 | 2/sqrt(пи) |
| M_SQRT2 | 1.41421356237309504880 | sqrt(2) |
| M_SQRT3 | 1.73205080756887729352 | sqrt(3) [4.0.2] |
| M_SQRT1_2 | 0.70710678118654752440 | 1/sqrt(2) |
| M_LNPI | 1.14472988584940017414 | ln пи [4.0.2] |
| M_EULER | 0.57721566490153286061 | Постоянная эйлера [4.0.2] |
Коментарии
There are also the predefined PHP_INT_MAX and PHP_INT_SIZE constants, that describe the range of possible integer values.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'
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)
?>
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.