Function Definition
The PHP pack() function converts data into binary strings using specified formatting rules. Syntax:
string pack(string $format, mixed $args, ...)Key Parameters
- format: String containing format codes (e.g., N, V, a*)
- args: Variables to pack (minimum 1 required)
Common Usage Examples
Example 1: Pack 32-bit integer
$binary = pack("N", 123456);Example 2: Multiple data types
$data = pack("a5n", "Hello", 255);Return Value
Returns binary string on success, FALSE on errors. Always validate inputs:
if ($binary === false) {
throw new Exception("Invalid pack() arguments");
}Important Considerations
- Format string errors cause unexpected results
- Byte order matters (N=big-endian, V=little-endian)
- Data truncation with fixed-length specifiers (a5)
- Binary safety when handling user inputs
Practical Applications
Use pack() for:
- Network protocol implementations
- File format creation (PDF headers, image formats)
- Database binary storage optimization
- Cross-system data exchange
Security Best Practices
When processing external data:
// Always sanitize before packing
$clean_int = filter_var($_POST['num'], FILTER_VALIDATE_INT);
$safe_binary = pack("N", $clean_int);