.TH "Stdlib.Printf" 3 2024-05-31 OCamldoc "OCaml library"
.SH NAME
Stdlib.Printf \- no description
.SH Module
Module   Stdlib.Printf
.SH Documentation
.sp
Module
.BI "Printf"
 : 
.B (module Stdlib__Printf)

.sp

.sp

.sp
.sp

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

.ft B
fprintf outchan format arg1 \&.\&.\&. argN
.ft R
formats the arguments
.ft B
arg1
.ft R
to 
.ft B
argN
.ft R
according to the format string 
.ft B
format
.ft R
, and
outputs the resulting string on the channel 
.ft B
outchan
.ft R
\&.
.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

.ft B
% [flags] [width] [\&.precision] type
.ft R
.sp
In short, a conversion specification consists in the 
.ft B
%
.ft R
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
\-
.ft B
d
.ft R
, 
.ft B
i
.ft R
: convert an integer argument to signed decimal\&.
The flag 
.ft B
#
.ft R
adds underscores to large values for readability\&.
.sp
\-
.ft B
u
.ft R
, 
.ft B
n
.ft R
, 
.ft B
l
.ft R
, 
.ft B
L
.ft R
, or 
.ft B
N
.ft R
: convert an integer argument to
unsigned decimal\&.  Warning: 
.ft B
n
.ft R
, 
.ft B
l
.ft R
, 
.ft B
L
.ft R
, and 
.ft B
N
.ft R
are
used for 
.ft B
scanf
.ft R
, and should not be used for 
.ft B
printf
.ft R
\&.
The flag 
.ft B
#
.ft R
adds underscores to large values for readability\&.
.sp
\-
.ft B
x
.ft R
: convert an integer argument to unsigned hexadecimal,
using lowercase letters\&.
The flag 
.ft B
#
.ft R
adds a 
.ft B
0x
.ft R
prefix to non zero values\&.
.sp
\-
.ft B
X
.ft R
: convert an integer argument to unsigned hexadecimal,
using uppercase letters\&.
The flag 
.ft B
#
.ft R
adds a 
.ft B
0X
.ft R
prefix to non zero values\&.
.sp
\-
.ft B
o
.ft R
: convert an integer argument to unsigned octal\&.
The flag 
.ft B
#
.ft R
adds a 
.ft B
0
.ft R
prefix to non zero values\&.
.sp
\-
.ft B
s
.ft R
: insert a string argument\&.
.sp
\-
.ft B
S
.ft R
: convert a string argument to OCaml syntax (double quotes, escapes)\&.
.sp
\-
.ft B
c
.ft R
: insert a character argument\&.
.sp
\-
.ft B
C
.ft R
: convert a character argument to OCaml syntax
(single quotes, escapes)\&.
.sp
\-
.ft B
f
.ft R
: convert a floating\-point argument to decimal notation,
in the style 
.ft B
dddd\&.ddd
.ft R
\&.
.sp
\-
.ft B
F
.ft R
: convert a floating\-point argument to OCaml syntax (
.ft B
dddd\&.
.ft R
or 
.ft B
dddd\&.ddd
.ft R
or 
.ft B
d\&.ddd e+\-dd
.ft R
)\&.
Converts to hexadecimal with the 
.ft B
#
.ft R
flag (see 
.ft B
h
.ft R
)\&.
.sp
\-
.ft B
e
.ft R
or 
.ft B
E
.ft R
: convert a floating\-point argument to decimal notation,
in the style 
.ft B
d\&.ddd e+\-dd
.ft R
(mantissa and exponent)\&.
.sp
\-
.ft B
g
.ft R
or 
.ft B
G
.ft R
: convert a floating\-point argument to decimal notation,
in style 
.ft B
f
.ft R
or 
.ft B
e
.ft R
, 
.ft B
E
.ft R
(whichever is more compact)\&. Moreover,
any trailing zeros are removed from the fractional part of the result
and the decimal\-point character is removed if there is no fractional
part remaining\&.
.sp
\-
.ft B
h
.ft R
or 
.ft B
H
.ft R
: convert a floating\-point argument to hexadecimal notation,
in the style 
.ft B
0xh\&.hhhh p+\-dd
.ft R
(hexadecimal mantissa, exponent in
decimal and denotes a power of 2)\&.
.sp
\-
.ft B
B
.ft R
: convert a boolean argument to the string 
.ft B
true
.ft R
or 
.ft B
false
.ft R

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

The optional 
.ft B
flags
.ft R
are:
.sp
\-
.ft B
\-
.ft R
: left\-justify the output (default is right justification)\&.
.sp
\-
.ft B
0
.ft R
: for numerical conversions, pad with zeroes instead of spaces\&.
.sp
\-
.ft B
+
.ft R
: for signed numerical conversions, prefix number with a 
.ft B
+
.ft R
sign if positive\&.
.sp
\-space: for signed numerical conversions, prefix number with a
space if positive\&.
.sp
\-
.ft B
#
.ft R
: request an alternate formatting style for the integer types
and the floating\-point type 
.ft B
F
.ft R
\&.

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

.sp

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

.sp

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

.sp

.I val sprintf 
: 
.B ('a, unit, string) format -> 'a
.sp
Same as 
.ft B
Printf\&.fprintf
.ft R
, 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) format -> 'a
.sp
Same as 
.ft B
Printf\&.fprintf
.ft R
, but instead of printing on an output channel,
append the formatted arguments to the given extensible buffer
(see module 
.ft B
Buffer
.ft R
)\&.

.sp

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

.sp
.B "Since"
3.10

.sp

.I val ibprintf 
: 
.B Buffer.t -> ('a, Buffer.t, unit) format -> 'a
.sp
Same as 
.ft B
Printf\&.bprintf
.ft R
, but does not print anything\&.
Useful to ignore some material when conditionally printing\&.

.sp
.B "Since"
4.11

.sp

.PP
Formatted output functions with continuations\&.
.PP

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

.sp
.B "Since"
3.09

.sp

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

.sp
.B "Since"
4.01

.sp

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

.sp
.B "Since"
3.09

.sp

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

.sp
.B "Since"
3.10

.sp

.I val ikbprintf 
: 
.B (Buffer.t -> 'd) ->
.B   Buffer.t -> ('a, Buffer.t, unit, 'd) format4 -> 'a
.sp
Same as 
.ft B
kbprintf
.ft R
above, but does not print anything\&.
Useful to ignore some material when conditionally printing\&.

.sp
.B "Since"
4.11

.sp

.PP
Deprecated
.PP

.I val kprintf 
: 
.B (string -> 'b) -> ('a, unit, string, 'b) format4 -> 'a
.sp
.B "Deprecated."
Use Printf\&.ksprintf instead\&.

.sp
A deprecated synonym for 
.ft B
ksprintf
.ft R
\&.

.sp