# BcMath\Number::sub

(PHP 8 >= 8.4.0)

BcMath\Number::sub — Subtracts an arbitrary precision number

### 说明

public BcMath\Number::sub(BcMath\Number|string|int `$num`, ?int `$scale` = `null`): BcMath\Number

Subtracts `num` from $this.

### 参数

`num`
  The value to subtract.
`scale`
  BcMath\Number::scale explicitly specified for calculation results. If `null`, the BcMath\Number::scale of the calculation result will be set automatically.

### 返回值

Returns the result of subtraction as a new BcMath\Number object.

When the BcMath\Number::scale of the result object is automatically set, the greater BcMath\Number::scale of the two numbers used for subtraction is used.

That is, if the BcMath\Number::scales of two values are `2` and `5` respectively, the BcMath\Number::scale of the result will be `5`.

### 错误／异常

This method throws a ValueError in the following cases:

- `num` is string and not a well-formed BCMath numeric string
- `scale` is outside the valid range

### 示例

示例 #1 BcMath\Number::sub() example when `scale` is not specified

`<?php
$number = new BcMath\Number('1.234');
$ret1 = $number->sub(new BcMath\Number('2.34567'));
$ret2 = $number->sub('-3.456');
$ret3 = $number->sub(7);
var_dump($number, $ret1, $ret2, $ret3);
?>`

以上示例会输出：

    object(BcMath\Number)#1 (2) {
      ["value"]=>
      string(5) "1.234"
      ["scale"]=>
      int(3)
    }
    object(BcMath\Number)#3 (2) {
      ["value"]=>
      string(8) "-1.11167"
      ["scale"]=>
      int(5)
    }
    object(BcMath\Number)#2 (2) {
      ["value"]=>
      string(5) "4.690"
      ["scale"]=>
      int(3)
    }
    object(BcMath\Number)#4 (2) {
      ["value"]=>
      string(6) "-5.766"
      ["scale"]=>
      int(3)
    }

示例 #2 BcMath\Number::sub() example of explicitly specifying `scale`

`<?php
$number = new BcMath\Number('1.234');
$ret1 = $number->sub(new BcMath\Number('2.34567'), 1);
$ret2 = $number->sub('-3.456', 10);
$ret3 = $number->sub(7, 0);
var_dump($number, $ret1, $ret2, $ret3);
?>`

以上示例会输出：

    object(BcMath\Number)#1 (2) {
      ["value"]=>
      string(5) "1.234"
      ["scale"]=>
      int(3)
    }
    object(BcMath\Number)#3 (2) {
      ["value"]=>
      string(4) "-1.1"
      ["scale"]=>
      int(1)
    }
    object(BcMath\Number)#2 (2) {
      ["value"]=>
      string(12) "4.6900000000"
      ["scale"]=>
      int(10)
    }
    object(BcMath\Number)#4 (2) {
      ["value"]=>
      string(2) "-5"
      ["scale"]=>
      int(0)
    }

### 参见

- bcsub() - 两个任意精度数字的减法
- BcMath\Number::add() - Adds an arbitrary precision number

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