format (ANSI and GNU Common Lisp Document)

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#### 22.4.31 format [Function]

`format` destination control-string &rest args ⇒ result

#### Arguments and Values::

destination—nil, t, a stream, or a string with a fill pointer.

control-string—a format control.

args—format arguments for control-string.

result—if destination is non-nil, then nil; otherwise, a string.

#### Description::

format produces formatted output by outputting the characters of control-string and observing that a tilde introduces a directive. The character after the tilde, possibly preceded by prefix parameters and modifiers, specifies what kind of formatting is desired. Most directives use one or more elements of args to create their output.

If destination is a string, a stream, or t, then the result is nil. Otherwise, the result is a string containing the ‘output.’

format is useful for producing nicely formatted text, producing good-looking messages, and so on. format can generate and return a string or output to destination.

For details on how the control-string is interpreted, see Formatted Output.

#### Affected By::

*standard-output*, *print-escape*, *print-radix*, *print-base*, *print-circle*, *print-pretty*, *print-level*, *print-length*, *print-case*, *print-gensym*, *print-array*.

#### Exceptional Situations::

If destination is a string with a fill pointer, the consequences are undefined if destructive modifications are performed directly on the string during the dynamic extent of the call.

#### See Also::

write , Documentation of Implementation-Defined Scripts