sprintf

With printf() and sprintf() functions, escape character is not backslash '\' but rather '%'.

Ie. to print '%' character you need to escape it with itself:
<?php
printf('%%%s%%', 'koko'); #output: '%koko%'
?>

1.  A plus sign ('+') means put a '+' before positive numbers while a minus sign ('-') means left justify.  The documentation incorrectly states that they are interchangeable.  They produce unique results that can be combined:

<?php
echo sprintf ("|%+4d|%+4d|\n",   1, -1);
echo sprintf ("|%-4d|%-4d|\n",   1, -1);
echo sprintf ("|%+-4d|%+-4d|\n", 1, -1);
?>

outputs:

|  +1|  -1|
|1   |-1  |
|+1  |-1  |

2.  Padding with a '0' is different than padding with other characters.  Zeros will only be added at the front of a number, after any sign.  Other characters will be added before the sign, or after the number:

<?php
echo sprintf ("|%04d|\n",   -2);
echo sprintf ("|%':4d|\n",  -2);
echo sprintf ("|%-':4d|\n", -2);

// Specifying both "-" and "0" creates a conflict with unexpected results:
echo sprintf ("|%-04d|\n",  -2);

// Padding with other digits behaves like other non-zero characters:
echo sprintf ("|%-'14d|\n", -2);
echo sprintf ("|%-'04d|\n", -2);
?>

outputs:

|-002|
|::-2|
|-2::|
|-2  |
|-211|
|-2  |

it is also worth to notice that Argnum starts from 1 and NOT 0

If the format string is enclosed in double-quotes (""), you need to escape the dollar sign after argnum with a backslash character (\), like this %1\$s, so that the PHP doesn't try to interpret them as variable. Using a backslash like this is called an escape sequence.

<?php
// Sample string
$number = 499;
$format = "The number without decimal points: %1\$d, and the number with two decimal points: %1\$.2f";

// Formatting and print the string
printf($format, $number);
?>

There are already some comments on using sprintf to force leading leading zeros but the examples only include integers. I needed leading zeros on floating point numbers and was surprised that it didn't work as expected.

Example:
<?php
sprintf('%02d', 1);
?>

This will result in 01. However, trying the same for a float with precision doesn't work:

<?php
sprintf('%02.2f', 1);
?>

Yields 1.00. 

This threw me a little off. To get the desired result, one needs to add the precision (2) and the length of the decimal seperator "." (1). So the correct pattern would be

<?php
sprintf('%05.2f', 1);
?>

Output: 01.00

Please see http://stackoverflow.com/a/28739819/413531 for a more detailed explanation.

Here is how to print a floating point number with 16 significant digits regardless of magnitude:

<?php
    $result = sprintf(sprintf('%%.%dF', max(15 - floor(log10($value)), 0)), $value);
?>

This works more reliably than doing something like sprintf('%.15F', $value) as the latter may cut off significant digits for very small numbers, or prints bogus digits (meaning extra digits beyond what can reliably be represented in a floating point number) for very large numbers.

A more complete and working version of mb_sprintf and mb_vsprintf. It should work with any "ASCII preserving" encoding such as UTF-8 and all the ISO-8859 charsets. It handles sign, padding, alignment, width and precision. Argument swapping is not handled.

<?php
if (!function_exists('mb_sprintf')) {
  function mb_sprintf($format) {
      $argv = func_get_args() ;
      array_shift($argv) ;
      return mb_vsprintf($format, $argv) ;
  }
}
if (!function_exists('mb_vsprintf')) {
  /**
   * Works with all encodings in format and arguments.
   * Supported: Sign, padding, alignment, width and precision.
   * Not supported: Argument swapping.
   */
  function mb_vsprintf($format, $argv, $encoding=null) {
      if (is_null($encoding))
          $encoding = mb_internal_encoding();

      // Use UTF-8 in the format so we can use the u flag in preg_split
      $format = mb_convert_encoding($format, 'UTF-8', $encoding);

      $newformat = ""; // build a new format in UTF-8
      $newargv = array(); // unhandled args in unchanged encoding

      while ($format !== "") {
      
        // Split the format in two parts: $pre and $post by the first %-directive
        // We get also the matched groups
        list ($pre, $sign, $filler, $align, $size, $precision, $type, $post) =
            preg_split("!\%(\+?)('.|[0 ]|)(-?)([1-9][0-9]*|)(\.[1-9][0-9]*|)([%a-zA-Z])!u",
                       $format, 2, PREG_SPLIT_DELIM_CAPTURE) ;

        $newformat .= mb_convert_encoding($pre, $encoding, 'UTF-8');
        
        if ($type == '') {
          // didn't match. do nothing. this is the last iteration.
        }
        elseif ($type == '%') {
          // an escaped %
          $newformat .= '%%';
        }
        elseif ($type == 's') {
          $arg = array_shift($argv);
          $arg = mb_convert_encoding($arg, 'UTF-8', $encoding);
          $padding_pre = '';
          $padding_post = '';
          
          // truncate $arg
          if ($precision !== '') {
            $precision = intval(substr($precision,1));
            if ($precision > 0 && mb_strlen($arg,$encoding) > $precision)
              $arg = mb_substr($precision,0,$precision,$encoding);
          }
          
          // define padding
          if ($size > 0) {
            $arglen = mb_strlen($arg, $encoding);
            if ($arglen < $size) {
              if($filler==='')
                  $filler = ' ';
              if ($align == '-')
                  $padding_post = str_repeat($filler, $size - $arglen);
              else
                  $padding_pre = str_repeat($filler, $size - $arglen);
            }
          }
          
          // escape % and pass it forward
          $newformat .= $padding_pre . str_replace('%', '%%', $arg) . $padding_post;
        }
        else {
          // another type, pass forward
          $newformat .= "%$sign$filler$align$size$precision$type";
          $newargv[] = array_shift($argv);
        }
        $format = strval($post);
      }
      // Convert new format back from UTF-8 to the original encoding
      $newformat = mb_convert_encoding($newformat, $encoding, 'UTF-8');
      return vsprintf($newformat, $newargv);
  }
}
?>

Encoding and decoding IP adress to format: 1A2B3C4D (mysql column: char(8) )

<?php
function encode_ip($dotquad_ip)
{
    $ip_sep = explode('.', $dotquad_ip);
    return sprintf('%02x%02x%02x%02x', $ip_sep[0], $ip_sep[1], $ip_sep[2], $ip_sep[3]);
}

function decode_ip($int_ip)
{
    $hexipbang = explode('.', chunk_split($int_ip, 2, '.'));
    return hexdec($hexipbang[0]). '.' . hexdec($hexipbang[1]) . '.' . hexdec($hexipbang[2]) . '.' . hexdec($hexipbang[3]);
}
?>

Here's a clean, working version of functions to allow using named arguments instead of numeric ones. ex: instead of sprintf('%1$s', 'Joe');, we can use sprintf('%name$s', array('name' => 'Joe'));. I've provided 2 different versions: the first uses the php-like syntax (ex: %name$s), while the second uses the python syntax (ex: %(name)s).

<?php

/**
 * version of sprintf for cases where named arguments are desired (php syntax)
 *
 * with sprintf: sprintf('second: %2$s ; first: %1$s', '1st', '2nd');
 *
 * with sprintfn: sprintfn('second: %second$s ; first: %first$s', array(
 *  'first' => '1st',
 *  'second'=> '2nd'
 * ));
 *
 * @param string $format sprintf format string, with any number of named arguments
 * @param array $args array of [ 'arg_name' => 'arg value', ... ] replacements to be made
 * @return string|false result of sprintf call, or bool false on error
 */
function sprintfn ($format, array $args = array()) {
    // map of argument names to their corresponding sprintf numeric argument value
    $arg_nums = array_slice(array_flip(array_keys(array(0 => 0) + $args)), 1);

    // find the next named argument. each search starts at the end of the previous replacement.
    for ($pos = 0; preg_match('/(?<=%)([a-zA-Z_]\w*)(?=\$)/', $format, $match, PREG_OFFSET_CAPTURE, $pos);) {
        $arg_pos = $match[0][1];
        $arg_len = strlen($match[0][0]);
        $arg_key = $match[1][0];

        // programmer did not supply a value for the named argument found in the format string
        if (! array_key_exists($arg_key, $arg_nums)) {
            user_error("sprintfn(): Missing argument '${arg_key}'", E_USER_WARNING);
            return false;
        }

        // replace the named argument with the corresponding numeric one
        $format = substr_replace($format, $replace = $arg_nums[$arg_key], $arg_pos, $arg_len);
        $pos = $arg_pos + strlen($replace); // skip to end of replacement for next iteration
    }

    return vsprintf($format, array_values($args));
}

/**
 * version of sprintf for cases where named arguments are desired (python syntax)
 *
 * with sprintf: sprintf('second: %2$s ; first: %1$s', '1st', '2nd');
 *
 * with sprintfn: sprintfn('second: %(second)s ; first: %(first)s', array(
 *  'first' => '1st',
 *  'second'=> '2nd'
 * ));
 *
 * @param string $format sprintf format string, with any number of named arguments
 * @param array $args array of [ 'arg_name' => 'arg value', ... ] replacements to be made
 * @return string|false result of sprintf call, or bool false on error
 */
function sprintfn ($format, array $args = array()) {
    // map of argument names to their corresponding sprintf numeric argument value
    $arg_nums = array_slice(array_flip(array_keys(array(0 => 0) + $args)), 1);

    // find the next named argument. each search starts at the end of the previous replacement.
    for ($pos = 0; preg_match('/(?<=%)\(([a-zA-Z_]\w*)\)/', $format, $match, PREG_OFFSET_CAPTURE, $pos);) {
        $arg_pos = $match[0][1];
        $arg_len = strlen($match[0][0]);
        $arg_key = $match[1][0];

        // programmer did not supply a value for the named argument found in the format string
        if (! array_key_exists($arg_key, $arg_nums)) {
            user_error("sprintfn(): Missing argument '${arg_key}'", E_USER_WARNING);
            return false;
        }

        // replace the named argument with the corresponding numeric one
        $format = substr_replace($format, $replace = $arg_nums[$arg_key] . '$', $arg_pos, $arg_len);
        $pos = $arg_pos + strlen($replace); // skip to end of replacement for next iteration
    }

    return vsprintf($format, array_values($args));
}

?>

Using argument swapping in sprintf() with gettext: Let's say you've written the following script:

<?php
$var = sprintf(gettext("The %2\$s contains %1\$d monkeys"), 2, "cage");
?>

Now you run xgettext in order to generate a .po file. The .po file will then look like this:

#: file.php:9
#, ycp-format
msgid "The %2\\$s contains %1\\$d monkeys"
msgstr ""

Notice how an extra backslash has been added by xgettext.

Once you've translated the string, you must remove all backslashes from the ID string as well as the translation, so the po file will look like this:

#: file.php:9
#, ycp-format
msgid "The %2$s contains %1$d monkeys"
msgstr "Der er %1$d aber i %2$s"

Now run msgfmt to generate the .mo file, restart Apache to remove the gettext cache if necessary, and you're off.

If you use the default padding specifier (a space) and then print it to HTML, you will notice that HTML does not display the multiple spaces correctly. This is because any sequence of white-space is treated as a single space.

To overcome this, I wrote a simple function that replaces all the spaces in the string returned by sprintf() with the character entity reference " " to achieve non-breaking space in strings returned by sprintf()

<?php
//Here is the function:
function sprintf_nbsp() {
   $args = func_get_args();
   return str_replace(' ', '&nbsp;', vsprintf(array_shift($args), array_values($args)));
}

//Usage (exactly like sprintf):
$format = 'The %d monkeys are attacking the [%10s]!';
$str = sprintf_nbsp($format, 15, 'zoo');
echo $str;
?>

The above example will output:
The 15 monkeys are attacking the [       zoo]!

<?php
//The variation that prints the string instead of returning it:
function printf_nbsp() {
   $args = func_get_args();
   echo str_replace(' ', '&nbsp;', vsprintf(array_shift($args), array_values($args)));
}
?>

I had a nightmare trying to find the two's complement of a 32 bit number.

I got this from http://www.webmasterworld.com/forum88/13334.htm (credit where credit is due... =P  )

Quote: ...find out the 2's complement of any number, which is -(pow(2, n) - N) where n is the number of bits and N is the number for which to find out its 2's complement.

This worked magic for me... previously I was trying to use

sprintf ("%b",$32BitDecimal);
But it always returned 10000000000000000000000 when the $32BitDecimal value got above 2,000,000,000.

This -(pow(2, n) - N)
Worked remarkably well and was very accurate.

Hope this helps someone fighting with two's complement in PHP.

$format = 'There are %1$d monkeys in the %s and %s ';
printf($format, 100, 'Chennai', 'Bangalore'); 

Expecting to output
"There are 100 monkeys in the Chennai and bangalore"

But, this will output 
"There are 100 monkeys in the 100 and Chennai"

Because, the second and Third specifiers takes 1rst and 2nd arguments. Because it is not assigned with any arguments.