It’s neither `0x`

nor `0`

; what is it? Is there?

As of PHP 5.4+ the prefix for binary number is:

```
0b
```

For ealier version, there is no such prefix. Instead, you can use `0x`

, for hexadecimal.

For more informations, see the **Integers section of the PHP manual**.

Still, if you really need to write values using binary before PHP 5.4, you can use the `bindec`

function, that takes a string containing the binary, and returns the corresponding value.

For example, the following portion of code :

```
echo bindec('10011');
```

Will get you :

```
19
```

But note you shouldn’t do that too often : calling a function to do that each time the script is executed is quite bad for performances ^^

Instead, it’s really a better solution to write your values using hexadecimal, where each digit codes for 4 bits.

### Answer：

New in PHP 5.4 is the binary prefix, `0b`

. Think about portability when using it though; you’ll need to be able to guarantee the server runs PHP 5.4+.

### Answer：

From PHP 5.4+ there is, in fact, a prefix: `0b`

.

Current info in PHP Docs:

Binary integer literals are available since PHP 5.4.0.

To use octal notation, precede the number with a 0 (zero). To use hexadecimal notation precede the number with 0x. To use binary notation precede the number with 0b.

**Mar 24 ’10 at 11:31 (original answer):**

I don’t think there is one. Prefix `0`

if for octal and `0x`

is for hexadecimal.

From PHP docs:

Integer can be specified in decimal (base 10), hexadecimal (base 16), or octal (base 8) notation, optionally preceded by a sign (- or +).

To use octal notation, precede the number with a 0 (zero). To use hexadecimal notation precede the number with 0x.

### Answer：

Check the manual: PHP only supports decimal, hexadecimal and octal integer notation, but you can use bindec() instead.

Also, keep in mind that each hex digit represents 4 bits, so it’s easy to convert between binary notation and hex. The same is true for octal, but for various reasons it’s used less often in practice.

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