.TH "Printf" 3o source: 2017-09-14 OCamldoc "OCaml library"
.SH NAME
Printf \- Formatted output functions.
.SH Module
Module   Printf
.SH Documentation
.sp
Module
.BI "Printf"
 : 
.B sig  end

.sp
Formatted output functions\&.

.sp

.sp
.sp

.I val fprintf 
: 
.B Pervasives.out_channel ->
.B   ('a, Pervasives.out_channel, unit) Pervasives.format -> 'a
.sp

.B fprintf outchan format arg1 \&.\&.\&. argN
formats the arguments
.B arg1
to 
.B argN
according to the format string 
.B format
, and
outputs the resulting string on the channel 
.B outchan
\&.
.sp
The format string is a character string which contains two types of
objects: plain characters, which are simply copied to the output
channel, and conversion specifications, each of which causes
conversion and printing of arguments\&.
.sp
Conversion specifications have the following form:
.sp

.B % [flags] [width] [\&.precision] type
.sp
In short, a conversion specification consists in the 
.B %
character,
followed by optional modifiers and a type which is made of one or
two characters\&.
.sp
The types and their meanings are:
.sp
.sp
\-
.B d
, 
.B i
: convert an integer argument to signed decimal\&.
.sp
\-
.B u
, 
.B n
, 
.B l
, 
.B L
, or 
.B N
: convert an integer argument to
unsigned decimal\&.  Warning: 
.B n
, 
.B l
, 
.B L
, and 
.B N
are
used for 
.B scanf
, and should not be used for 
.B printf
\&.
.sp
\-
.B x
: convert an integer argument to unsigned hexadecimal,
using lowercase letters\&.
.sp
\-
.B X
: convert an integer argument to unsigned hexadecimal,
using uppercase letters\&.
.sp
\-
.B o
: convert an integer argument to unsigned octal\&.
.sp
\-
.B s
: insert a string argument\&.
.sp
\-
.B S
: convert a string argument to OCaml syntax (double quotes, escapes)\&.
.sp
\-
.B c
: insert a character argument\&.
.sp
\-
.B C
: convert a character argument to OCaml syntax
(single quotes, escapes)\&.
.sp
\-
.B f
: convert a floating\-point argument to decimal notation,
in the style 
.B dddd\&.ddd
\&.
.sp
\-
.B F
: convert a floating\-point argument to OCaml syntax (
.B dddd\&.
or 
.B dddd\&.ddd
or 
.B d\&.ddd e+\-dd
)\&.
.sp
\-
.B e
or 
.B E
: convert a floating\-point argument to decimal notation,
in the style 
.B d\&.ddd e+\-dd
(mantissa and exponent)\&.
.sp
\-
.B g
or 
.B G
: convert a floating\-point argument to decimal notation,
in style 
.B f
or 
.B e
, 
.B E
(whichever is more compact)\&.
.sp
\-
.B h
or 
.B H
: convert a floating\-point argument to hexadecimal notation,
in the style 
.B 0xh\&.hhhh e+\-dd
(hexadecimal mantissa, exponent in
decimal and denotes a power of 2)\&.
.sp
\-
.B B
: convert a boolean argument to the string 
.B true
or 
.B false

.sp
\-
.B b
: convert a boolean argument (deprecated; do not use in new
programs)\&.
.sp
\-
.B ld
, 
.B li
, 
.B lu
, 
.B lx
, 
.B lX
, 
.B lo
: convert an 
.B int32
argument to
the format specified by the second letter (decimal, hexadecimal, etc)\&.
.sp
\-
.B nd
, 
.B ni
, 
.B nu
, 
.B nx
, 
.B nX
, 
.B no
: convert a 
.B nativeint
argument to
the format specified by the second letter\&.
.sp
\-
.B Ld
, 
.B Li
, 
.B Lu
, 
.B Lx
, 
.B LX
, 
.B Lo
: convert an 
.B int64
argument to
the format specified by the second letter\&.
.sp
\-
.B a
: user\-defined printer\&. Take two arguments and apply the
first one to 
.B outchan
(the current output channel) and to the
second argument\&. The first argument must therefore have type
.B out_channel \-> \&'b \-> unit
and the second 
.B \&'b
\&.
The output produced by the function is inserted in the output of
.B fprintf
at the current point\&.
.sp
\-
.B t
: same as 
.B %a
, but take only one argument (with type
.B out_channel \-> unit
) and apply it to 
.B outchan
\&.
.sp
\-
.B { fmt %}
: convert a format string argument to its type digest\&.
The argument must have the same type as the internal format string
.B fmt
\&.
.sp
\-
.B ( fmt %)
: format string substitution\&. Take a format string
argument and substitute it to the internal format string 
.B fmt
to print following arguments\&. The argument must have the same
type as the internal format string 
.B fmt
\&.
.sp
\-
.B !
: take no argument and flush the output\&.
.sp
\-
.B %
: take no argument and output one 
.B %
character\&.
.sp
\-
.B @
: take no argument and output one 
.B @
character\&.
.sp
\-
.B ,
: take no argument and output nothing: a no\-op delimiter for
conversion specifications\&.

The optional 
.B flags
are:
.sp
\-
.B \-
: left\-justify the output (default is right justification)\&.
.sp
\-
.B 0
: for numerical conversions, pad with zeroes instead of spaces\&.
.sp
\-
.B +
: for signed numerical conversions, prefix number with a 
.B +
sign if positive\&.
.sp
\-space: for signed numerical conversions, prefix number with a
space if positive\&.
.sp
\-
.B #
: request an alternate formatting style for the hexadecimal
and octal integer types (
.B x
, 
.B X
, 
.B o
, 
.B lx
, 
.B lX
, 
.B lo
, 
.B Lx
,
.B LX
, 
.B Lo
)\&.

The optional 
.B width
is an integer indicating the minimal
width of the result\&. For instance, 
.B %6d
prints an integer,
prefixing it with spaces to fill at least 6 characters\&.
.sp
The optional 
.B precision
is a dot 
.B \&.
followed by an integer
indicating how many digits follow the decimal point in the 
.B %f
,
.B %e
, and 
.B %E
conversions\&. For instance, 
.B %\&.4f
prints a 
.B float
with
4 fractional digits\&.
.sp
The integer in a 
.B width
or 
.B precision
can also be specified as
.B *
, in which case an extra integer argument is taken to specify
the corresponding 
.B width
or 
.B precision
\&. This integer argument
precedes immediately the argument to print\&.
For instance, 
.B %\&.*f
prints a 
.B float
with as many fractional
digits as the value of the argument given before the float\&.

.sp

.I val printf 
: 
.B ('a, Pervasives.out_channel, unit) Pervasives.format -> 'a
.sp
Same as 
.B Printf\&.fprintf
, but output on 
.B stdout
\&.

.sp

.I val eprintf 
: 
.B ('a, Pervasives.out_channel, unit) Pervasives.format -> 'a
.sp
Same as 
.B Printf\&.fprintf
, but output on 
.B stderr
\&.

.sp

.I val sprintf 
: 
.B ('a, unit, string) Pervasives.format -> 'a
.sp
Same as 
.B Printf\&.fprintf
, but instead of printing on an output channel,
return a string containing the result of formatting the arguments\&.

.sp

.I val bprintf 
: 
.B Buffer.t -> ('a, Buffer.t, unit) Pervasives.format -> 'a
.sp
Same as 
.B Printf\&.fprintf
, but instead of printing on an output channel,
append the formatted arguments to the given extensible buffer
(see module 
.B Buffer
)\&.

.sp

.I val ifprintf 
: 
.B 'b -> ('a, 'b, 'c, unit) Pervasives.format4 -> 'a
.sp
Same as 
.B Printf\&.fprintf
, but does not print anything\&.
Useful to ignore some material when conditionally printing\&.

.sp
.B "Since"
3.10.0

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.PP

.B === Formatted output functions with continuations\&. ===

.PP

.I val kfprintf 
: 
.B (Pervasives.out_channel -> 'd) ->
.B   Pervasives.out_channel ->
.B   ('a, Pervasives.out_channel, unit, 'd) Pervasives.format4 -> 'a
.sp
Same as 
.B fprintf
, but instead of returning immediately,
passes the out channel to its first argument at the end of printing\&.

.sp
.B "Since"
3.09.0

.sp

.I val ikfprintf 
: 
.B ('b -> 'd) -> 'b -> ('a, 'b, 'c, 'd) Pervasives.format4 -> 'a
.sp
Same as 
.B kfprintf
above, but does not print anything\&.
Useful to ignore some material when conditionally printing\&.

.sp
.B "Since"
4.01.0

.sp

.I val ksprintf 
: 
.B (string -> 'd) -> ('a, unit, string, 'd) Pervasives.format4 -> 'a
.sp
Same as 
.B sprintf
above, but instead of returning the string,
passes it to the first argument\&.

.sp
.B "Since"
3.09.0

.sp

.I val kbprintf 
: 
.B (Buffer.t -> 'd) ->
.B   Buffer.t -> ('a, Buffer.t, unit, 'd) Pervasives.format4 -> 'a
.sp
Same as 
.B bprintf
, but instead of returning immediately,
passes the buffer to its first argument at the end of printing\&.

.sp
.B "Since"
3.10.0

.sp

.PP

.B === Deprecated ===

.PP

.I val kprintf 
: 
.B (string -> 'b) -> ('a, unit, string, 'b) Pervasives.format4 -> 'a
.sp
A deprecated synonym for 
.B ksprintf
\&.

.sp