Printf (3)
NAME
Printf - Formatted output functions.Module
Module PrintfDocumentation
Module
Printf
:
sig end
Formatted output functions.
val fprintf
:
Pervasives.out_channel ->
('a, Pervasives.out_channel, unit) Pervasives.format -> 'a
fprintf outchan format arg1 ... argN
formats the arguments
arg1
to
argN
according to the format string
format
, and
outputs the resulting string on the channel
outchan
.
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.
Conversion specifications have the following form:
% [flags] [width] [.precision] type
In short, a conversion specification consists in the % character, followed by optional modifiers and a type which is made of one or two characters.
The types and their meanings are:
- d , i : convert an integer argument to signed decimal.
- u , n , l , L , or N : convert an integer argument to unsigned decimal. Warning: n , l , L , and N are used for scanf , and should not be used for printf .
- x : convert an integer argument to unsigned hexadecimal, using lowercase letters.
- X : convert an integer argument to unsigned hexadecimal, using uppercase letters.
- o : convert an integer argument to unsigned octal.
- s : insert a string argument.
- S : convert a string argument to OCaml syntax (double quotes, escapes).
- c : insert a character argument.
- C : convert a character argument to OCaml syntax (single quotes, escapes).
- f : convert a floating-point argument to decimal notation, in the style dddd.ddd .
- F : convert a floating-point argument to OCaml syntax ( dddd. or dddd.ddd or d.ddd e+-dd ).
- e or E : convert a floating-point argument to decimal notation, in the style d.ddd e+-dd (mantissa and exponent).
- g or G : convert a floating-point argument to decimal notation, in style f or e , E (whichever is more compact).
- h or H : convert a floating-point argument to hexadecimal notation, in the style 0xh.hhhh e+-dd (hexadecimal mantissa, exponent in decimal and denotes a power of 2).
-
B
: convert a boolean argument to the string
true
or
false
- b : convert a boolean argument (deprecated; do not use in new programs).
- ld , li , lu , lx , lX , lo : convert an int32 argument to the format specified by the second letter (decimal, hexadecimal, etc).
- nd , ni , nu , nx , nX , no : convert a nativeint argument to the format specified by the second letter.
- Ld , Li , Lu , Lx , LX , Lo : convert an int64 argument to the format specified by the second letter.
- a : user-defined printer. Take two arguments and apply the first one to outchan (the current output channel) and to the second argument. The first argument must therefore have type out_channel -> 'b -> unit and the second 'b . The output produced by the function is inserted in the output of fprintf at the current point.
- t : same as %a , but take only one argument (with type out_channel -> unit ) and apply it to outchan .
- { fmt %} : convert a format string argument to its type digest. The argument must have the same type as the internal format string fmt .
- ( fmt %) : format string substitution. Take a format string argument and substitute it to the internal format string fmt to print following arguments. The argument must have the same type as the internal format string fmt .
- ! : take no argument and flush the output.
- % : take no argument and output one % character.
- @ : take no argument and output one @ character.
-
,
: take no argument and output nothing: a no-op delimiter for
conversion specifications.
The optional
flags
are:
- - : left-justify the output (default is right justification).
- 0 : for numerical conversions, pad with zeroes instead of spaces.
- + : for signed numerical conversions, prefix number with a + sign if positive.
-space: for signed numerical conversions, prefix number with a space if positive.
-
#
: request an alternate formatting style for the hexadecimal
and octal integer types (
x
,
X
,
o
,
lx
,
lX
,
lo
,
Lx
,
LX
,
Lo
).
The optional
width
is an integer indicating the minimal
width of the result. For instance,
%6d
prints an integer,
prefixing it with spaces to fill at least 6 characters.
The optional precision is a dot . followed by an integer indicating how many digits follow the decimal point in the %f , %e , and %E conversions. For instance, %.4f prints a float with 4 fractional digits.
The integer in a
width
or
precision
can also be specified as
*
, in which case an extra integer argument is taken to specify
the corresponding
width
or
precision
. This integer argument
precedes immediately the argument to print.
For instance,
%.*f
prints a
float
with as many fractional
digits as the value of the argument given before the float.
val printf
:
('a, Pervasives.out_channel, unit) Pervasives.format -> 'a
Same as
Printf.fprintf
, but output on
stdout
.
val eprintf
:
('a, Pervasives.out_channel, unit) Pervasives.format -> 'a
Same as
Printf.fprintf
, but output on
stderr
.
val sprintf
:
('a, unit, string) Pervasives.format -> 'a
Same as
Printf.fprintf
, but instead of printing on an output channel,
return a string containing the result of formatting the arguments.
val bprintf
:
Buffer.t -> ('a, Buffer.t, unit) Pervasives.format -> 'a
Same as
Printf.fprintf
, but instead of printing on an output channel,
append the formatted arguments to the given extensible buffer
(see module
Buffer
).
val ifprintf
:
'b -> ('a, 'b, 'c, unit) Pervasives.format4 -> 'a
Same as
Printf.fprintf
, but does not print anything.
Useful to ignore some material when conditionally printing.
Since
3.10.0
=== Formatted output functions with continuations. ===
val kfprintf
:
(Pervasives.out_channel -> 'd) ->
Pervasives.out_channel ->
('a, Pervasives.out_channel, unit, 'd) Pervasives.format4 -> 'a
Same as
fprintf
, but instead of returning immediately,
passes the out channel to its first argument at the end of printing.
Since
3.09.0
val ikfprintf
:
('b -> 'd) -> 'b -> ('a, 'b, 'c, 'd) Pervasives.format4 -> 'a
Same as
kfprintf
above, but does not print anything.
Useful to ignore some material when conditionally printing.
Since
4.0
val ksprintf
:
(string -> 'd) -> ('a, unit, string, 'd) Pervasives.format4 -> 'a
Same as
sprintf
above, but instead of returning the string,
passes it to the first argument.
Since
3.09.0
val kbprintf
:
(Buffer.t -> 'd) ->
Buffer.t -> ('a, Buffer.t, unit, 'd) Pervasives.format4 -> 'a
Same as
bprintf
, but instead of returning immediately,
passes the buffer to its first argument at the end of printing.
Since
3.10.0
=== Deprecated ===
val kprintf
:
(string -> 'b) -> ('a, unit, string, 'b) Pervasives.format4 -> 'a
A deprecated synonym for
ksprintf
.