美国的邮政编码格式很简单，易于实现标准化和检验。其格式是5个数字，后面还可能有一个破折号及4个数字。虽然这种格式很简单，但判断输入的邮政编码是否实际存在还是有一定困难的，基本方法就是查看当前有效编码列表，而这些列表必须从美国邮政局才能得到。因此，程序清单11.2.1里的邮政编码处理库只实现了格式标准化及检验。
程序清单11.2.1 邮政编码函数库
<?php
// A function that will accept US zip codes
// and standardize them to xxxxx-xxxx format.
function standardize_zip($input) {
// First, remove all non-digits from the string
$digits = preg_replace('/[^0-9]/', '', $input);
// Grab the first five digits:
$ret = substr($digits, 0, 5);
// If there are more than 5, then include the rest after a dash
if (strlen($digits) > 5) {
$ret .= '-' . substr($digits, 5);
}
return $ret;
}
// A function to check for zip code validity
// It must have been standardized first.
function validate_zip($input) {
// First split the number into 2 parts:
$parts = explode('-', $input);
// If the first part is not 5 digits - Invalid
if (strlen($parts[0]) != 5) {
return false;
}
// If the second part exists, and is not 4 digits - Invalid
if (isset($parts[1]) && (strlen($parts[1]) != 4)) {
return false;
}
// Otherwise, we made it, it's valid.
return true;
}
// Standardize & validate some zips:
$zips = array('21771', '7177', 'x234 56', '12345-6789', '1313122',
'14142-77743', '21705-123', '2177-1234', '1-1', '7.42');
foreach ($zips as $num) {
$st = standardize_zip($num);
$valid = validate_zip($st);
$output = $valid ? 'Valid' : 'Invalid';
echo "<p>{$st} - {$output}</p>\n";
}
?>