SWI-Prolog 10.0.2 Reference Manual: Section A.29

## A.29 library(writef): Old-style formatted write

copyright
  Copied from Edinburgh C-Prolog. Original version by Byrd, changed many times since.

This library provides writef/1 and friends. These predicates originate from Edinburgh C-Prolog and and provided for compatibility purposes. New code should use format/1, format/2 and friends, which are currently supported by more Prolog implementations.

The writef-family of predicates conflicts with the modern character-esacapes flag about the interpretation of `\`-sequences. This can be avoided by

1. Disable character escapes (not recommended unless one wants to run really outdated code unmodified).
2. Double the `\` for conflicting interpretations
3. Use ISO compliant alternatives for conflicting interpretations

[det]writef(+Format)
[det]writef(+Format, +Arguments)
  Formatted write to the `current_output`. Format is a format specifier. Some escape sequences require arguments that must be provided in the list Arguments. There are two types of escape sequences: special characters start with `\` and include arguments start with `%`. The special character sequences are:

  > ``\n`` | Output a newline character
  > ``\l`` | Output a line separator (same as ``\n``)
  > ``\r`` | Output a carriage-return character (ASCII 13)
  > ``\r`` | Output a TAB character (ASCII 9)
  > ``\\`` | Output ``\``
  > ``\`%` | Output ``%``
  > ``\`nnn` | Output character <nnn>. <nnn> is a 1-3 decimal number

  Escape sequences to include arguments from Arguments. Each time a %-escape sequence is found in Format the next argument from Arguments is formatted according to the specification.

  > `%` | print/1 the next item (mnemonic: term)
  > `%` | write/1 the next item
  > `%` | writeq/1 the next item
  > `%` | display/1 the next item
  > `%` | Put the next item as a character
  > `%` | Write the next item N times where N is the second item (an integer)
  > `%` | Write the next item as a String (so it must be a list of characters)
  > `%` | Perform a ttyflush/0 (no items used)
  > `%Nc` | Write the next item Centered in N columns.
  > `%Nl` | Write the next item Left justified in N columns.
  > `%Nr` | Write the next item Right justified in N columns.

  deprecated
    New code should use format/1, format/2, etc.
[det]swritef(-String, +Format)
[det]swritef(-String, +Format, +Arguments)
  Use writef/1 or writef/2 and write the result to a string. Note that this is a string in the sense of string_codes/2, not a list of `character(-code)`s.
  deprecated
    . See format/2,3 and/or with_output_to/2.