1Printf(3)                        OCaml library                       Printf(3)
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NAME

6       Printf - Formatted output functions.
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Module

9       Module   Printf
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Documentation

12       Module Printf
13        : sig end
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16       Formatted output functions.
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23       val fprintf : out_channel -> ('a, out_channel, unit) format -> 'a
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26       fprintf outchan format arg1 ... argN formats the arguments arg1 to argN
27       according to the format string  format  ,  and  outputs  the  resulting
28       string on the channel outchan .
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30       The  format  string  is  a character string which contains two types of
31       objects: plain characters, which are simply copied to the output  chan‐
32       nel, and conversion specifications, each of which causes conversion and
33       printing of arguments.
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35       Conversion specifications have the following form:
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38       % [flags] [width] [.precision] type
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40       In short, a conversion specification consists in the % character,  fol‐
41       lowed  by  optional  modifiers  and  a type which is made of one or two
42       characters.
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44       The types and their meanings are:
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46
47       - d , i : convert an integer argument to signed decimal.   The  flag  #
48       adds underscores to large values for readability.
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50       -  u , n , l , L , or N : convert an integer argument to unsigned deci‐
51       mal.  Warning: n , l , L , and N are used for scanf , and should not be
52       used  for  printf  .   The  flag # adds underscores to large values for
53       readability.
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55       - x : convert an integer argument to unsigned hexadecimal, using lower‐
56       case letters.  The flag # adds a 0x prefix to non zero values.
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58       - X : convert an integer argument to unsigned hexadecimal, using upper‐
59       case letters.  The flag # adds a 0X prefix to non zero values.
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61       - o : convert an integer argument to unsigned octal.  The flag # adds a
62       0 prefix to non zero values.
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64       - s : insert a string argument.
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66       -  S  :  convert  a  string  argument  to  OCaml syntax (double quotes,
67       escapes).
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69       - c : insert a character argument.
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71       - C : convert a character argument  to  OCaml  syntax  (single  quotes,
72       escapes).
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74       -  f  :  convert  a floating-point argument to decimal notation, in the
75       style dddd.ddd .
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77       - F : convert a floating-point argument to OCaml  syntax  (  dddd.   or
78       dddd.ddd  or  d.ddd  e+-dd  ).  Converts to hexadecimal with the # flag
79       (see h ).
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81       - e or E : convert a floating-point argument to  decimal  notation,  in
82       the style d.ddd e+-dd (mantissa and exponent).
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84       -  g  or  G : convert a floating-point argument to decimal notation, in
85       style f or e , E (whichever is more compact).  Moreover,  any  trailing
86       zeros  are removed from the fractional part of the result and the deci‐
87       mal-point character is removed if there is no fractional  part  remain‐
88       ing.
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90       -  h  or H : convert a floating-point argument to hexadecimal notation,
91       in the style 0xh.hhhh p+-dd (hexadecimal mantissa, exponent in  decimal
92       and denotes a power of 2).
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94       - B : convert a boolean argument to the string true or false
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97       -  b  :  convert a boolean argument (deprecated; do not use in new pro‐
98       grams).
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100       - ld , li , lu , lx , lX , lo : convert an int32 argument to the format
101       specified by the second letter (decimal, hexadecimal, etc).
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103       -  nd  ,  ni  , nu , nx , nX , no : convert a nativeint argument to the
104       format specified by the second letter.
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106       - Ld , Li , Lu , Lx , LX , Lo : convert an int64 argument to the format
107       specified by the second letter.
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109       -  a : user-defined printer. Take two arguments and apply the first one
110       to outchan (the current output channel) and to the second argument. The
111       first  argument  must therefore have type out_channel -> 'b -> unit and
112       the second 'b .  The output produced by the function is inserted in the
113       output of fprintf at the current point.
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115       - t : same as %a , but take only one argument (with type out_channel ->
116       unit ) and apply it to outchan .
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118       - { fmt %} : convert a format string argument to its type digest.   The
119       argument must have the same type as the internal format string fmt .
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121       -  ( fmt %) : format string substitution. Take a format string argument
122       and substitute it to the internal format string fmt to print  following
123       arguments.  The argument must have the same type as the internal format
124       string fmt .
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126       - !  : take no argument and flush the output.
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128       - % : take no argument and output one % character.
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130       - @ : take no argument and output one @ character.
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132       - , : take no argument and output nothing: a no-op delimiter  for  con‐
133       version specifications.
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135       The optional flags are:
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137       - - : left-justify the output (default is right justification).
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139       - 0 : for numerical conversions, pad with zeroes instead of spaces.
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141       -  + : for signed numerical conversions, prefix number with a + sign if
142       positive.
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144       -space: for signed numerical conversions, prefix number with a space if
145       positive.
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147       -  #  : request an alternate formatting style for the integer types and
148       the floating-point type F .
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150       The optional width is an integer indicating the minimal  width  of  the
151       result.  For  instance, %6d prints an integer, prefixing it with spaces
152       to fill at least 6 characters.
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154       The optional precision is a dot .  followed by  an  integer  indicating
155       how many digits follow the decimal point in the %f , %e , %E , %h , and
156       %H conversions or the maximum number of significant  digits  to  appear
157       for  the %F , %g and %G conversions.  For instance, %.4f prints a float
158       with 4 fractional digits.
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160       The integer in a width or precision can also be specified  as  *  ,  in
161       which  case  an  extra  integer argument is taken to specify the corre‐
162       sponding width or precision . This integer  argument  precedes  immedi‐
163       ately the argument to print.  For instance, %.*f prints a float with as
164       many fractional digits as the value of the argument  given  before  the
165       float.
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169       val printf : ('a, out_channel, unit) format -> 'a
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171       Same as Printf.fprintf , but output on stdout .
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175       val eprintf : ('a, out_channel, unit) format -> 'a
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177       Same as Printf.fprintf , but output on stderr .
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181       val sprintf : ('a, unit, string) format -> 'a
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183       Same  as Printf.fprintf , but instead of printing on an output channel,
184       return a string containing the result of formatting the arguments.
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188       val bprintf : Buffer.t -> ('a, Buffer.t, unit) format -> 'a
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190       Same as Printf.fprintf , but instead of printing on an output  channel,
191       append the formatted arguments to the given extensible buffer (see mod‐
192       ule Buffer ).
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196       val ifprintf : 'b -> ('a, 'b, 'c, unit) format4 -> 'a
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198       Same as Printf.fprintf , but does not print anything.  Useful to ignore
199       some material when conditionally printing.
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201
202       Since 3.10.0
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206       val ibprintf : Buffer.t -> ('a, Buffer.t, unit) format -> 'a
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208       Same as Printf.bprintf , but does not print anything.  Useful to ignore
209       some material when conditionally printing.
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212       Since 4.11.0
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217       Formatted output functions with continuations.
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219       val kfprintf : (out_channel -> 'd) -> out_channel -> ('a,  out_channel,
220       unit, 'd) format4 -> 'a
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222       Same  as fprintf , but instead of returning immediately, passes the out
223       channel to its first argument at the end of printing.
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226       Since 3.09.0
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230       val ikfprintf : ('b -> 'd) -> 'b -> ('a, 'b, 'c, 'd) format4 -> 'a
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232       Same as kfprintf above, but does not print anything.  Useful to  ignore
233       some material when conditionally printing.
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236       Since 4.01.0
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240       val ksprintf : (string -> 'd) -> ('a, unit, string, 'd) format4 -> 'a
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242       Same  as  sprintf above, but instead of returning the string, passes it
243       to the first argument.
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246       Since 3.09.0
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250       val kbprintf : (Buffer.t -> 'd) -> Buffer.t -> ('a, Buffer.t, unit, 'd)
251       format4 -> 'a
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253       Same as bprintf , but instead of returning immediately, passes the buf‐
254       fer to its first argument at the end of printing.
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257       Since 3.10.0
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261       val ikbprintf : (Buffer.t -> 'd) -> Buffer.t ->  ('a,  Buffer.t,  unit,
262       'd) format4 -> 'a
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264       Same  as kbprintf above, but does not print anything.  Useful to ignore
265       some material when conditionally printing.
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268       Since 4.11.0
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273       Deprecated
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275       val kprintf : (string -> 'b) -> ('a, unit, string, 'b) format4 -> 'a
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277       A deprecated synonym for ksprintf .
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283OCamldoc                          2020-09-01                         Printf(3)