PHP 在一位数之前预先添加前导零，即时
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PHP prepend leading zero before single digit number, on-the-fly
提问by Ben
PHP - Is there a quick, on-the-fly method to test for a single character string, then prepend a leading zero?
PHP - 是否有一种快速、即时的方法来测试单个字符串，然后在前面加上前导零？
Example:
例子：
$year = 11;
$month = 4;
$stamp = $year.add_single_zero_if_needed($month); // Imaginary function
echo $stamp; // 1104
回答by Kirk Beard
You can use sprintf: http://php.net/manual/en/function.sprintf.php
您可以使用 sprintf：http: //php.net/manual/en/function.sprintf.php
<?php
$num = 4;
$num_padded = sprintf("%02d", $num);
echo $num_padded; // returns 04
?>
It will only add the zero if it's less than the required number of characters.
如果它少于所需的字符数，它只会添加零。
Edit: As pointed out by @FelipeAls:
编辑：正如@FelipeAls 所指出的：
When working with numbers, you should use %d(rather than %s), especially when there is the potential for negative numbers. If you're only using positive numbers, either option works fine.
处理数字时，您应该使用%d(而不是%s)，尤其是在可能出现负数时。如果您只使用正数，则任一选项都可以正常工作。
For example:
例如：
sprintf("%04s", 10);returns 0010sprintf("%04s", -10);returns 0-10
sprintf("%04s", 10);返回 0010sprintf("%04s", -10);返回 0-10
Where as:
然而：
sprintf("%04d", 10);returns 0010sprintf("%04d", -10);returns -010
sprintf("%04d", 10);返回 0010sprintf("%04d", -10);返回 -010
回答by Gaurav
You can use str_padfor adding 0's
您可以str_pad用于添加 0
str_pad($month, 2, '0', STR_PAD_LEFT);
string str_pad ( string $input , int $pad_length [, string $pad_string = " " [, int $pad_type = STR_PAD_RIGHT ]] )
string str_pad ( string $input , int $pad_length [, string $pad_string = " " [, int $pad_type = STR_PAD_RIGHT ]] )
回答by deceze
The universal tool for string formatting, sprintf:
字符串格式化的通用工具，sprintf：
$stamp = sprintf('%s%02s', $year, $month);
