1Printf(3)                          OCamldoc                          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  :  Pervasives.out_channel -> ('a, Pervasives.out_channel,
24       unit) Pervasives.format -> 'a
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26
27       fprintf outchan format arg1 ... argN formats the arguments arg1 to argN
28       according  to  the  format  string  format  , and outputs the resulting
29       string on the channel outchan .
30
31       The format string is a character string which  contains  two  types  of
32       objects:  plain characters, which are simply copied to the output chan‐
33       nel, and conversion specifications, each of which causes conversion and
34       printing of arguments.
35
36       Conversion specifications have the following form:
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39       % [flags] [width] [.precision] type
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41       In  short, a conversion specification consists in the % character, fol‐
42       lowed by optional modifiers and a type which is  made  of  one  or  two
43       characters.
44
45       The types and their meanings are:
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48       - d , i : convert an integer argument to signed decimal.
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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 .
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54       - x : convert an integer argument to unsigned hexadecimal, using lower‐
55       case letters.
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57       - X : convert an integer argument to unsigned hexadecimal, using upper‐
58       case letters.
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60       - o : convert an integer argument to unsigned octal.
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62       - s : insert a string argument.
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64       -  S  :  convert  a  string  argument  to  OCaml syntax (double quotes,
65       escapes).
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67       - c : insert a character argument.
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69       - C : convert a character argument  to  OCaml  syntax  (single  quotes,
70       escapes).
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72       -  f  :  convert  a floating-point argument to decimal notation, in the
73       style dddd.ddd .
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75       - F : convert a floating-point argument to OCaml  syntax  (  dddd.   or
76       dddd.ddd or d.ddd e+-dd ).
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78       -  e  or  E : convert a floating-point argument to decimal notation, in
79       the style d.ddd e+-dd (mantissa and exponent).
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81       - g or G : convert a floating-point argument to  decimal  notation,  in
82       style f or e , E (whichever is more compact).
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84       -  h  or H : convert a floating-point argument to hexadecimal notation,
85       in the style 0xh.hhhh e+-dd (hexadecimal mantissa, exponent in  decimal
86       and denotes a power of 2).
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88       - B : convert a boolean argument to the string true or false
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91       -  b  :  convert a boolean argument (deprecated; do not use in new pro‐
92       grams).
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94       - ld , li , lu , lx , lX , lo : convert an int32 argument to the format
95       specified by the second letter (decimal, hexadecimal, etc).
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97       -  nd  ,  ni  , nu , nx , nX , no : convert a nativeint argument to the
98       format specified by the second letter.
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100       - Ld , Li , Lu , Lx , LX , Lo : convert an int64 argument to the format
101       specified by the second letter.
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103       -  a : user-defined printer. Take two arguments and apply the first one
104       to outchan (the current output channel) and to the second argument. The
105       first  argument  must therefore have type out_channel -> 'b -> unit and
106       the second 'b .  The output produced by the function is inserted in the
107       output of fprintf at the current point.
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109       - t : same as %a , but take only one argument (with type out_channel ->
110       unit ) and apply it to outchan .
111
112       - { fmt %} : convert a format string argument to its type digest.   The
113       argument must have the same type as the internal format string fmt .
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115       -  ( fmt %) : format string substitution. Take a format string argument
116       and substitute it to the internal format string fmt to print  following
117       arguments.  The argument must have the same type as the internal format
118       string fmt .
119
120       - !  : take no argument and flush the output.
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122       - % : take no argument and output one % character.
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124       - @ : take no argument and output one @ character.
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126       - , : take no argument and output nothing: a no-op delimiter  for  con‐
127       version specifications.
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129       The optional flags are:
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131       - - : left-justify the output (default is right justification).
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133       - 0 : for numerical conversions, pad with zeroes instead of spaces.
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135       -  + : for signed numerical conversions, prefix number with a + sign if
136       positive.
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138       -space: for signed numerical conversions, prefix number with a space if
139       positive.
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141       -  #  :  request  an alternate formatting style for the hexadecimal and
142       octal integer types ( x , X , o , lx , lX , lo , Lx , LX , Lo ).
143
144       The optional width is an integer indicating the minimal  width  of  the
145       result.  For  instance, %6d prints an integer, prefixing it with spaces
146       to fill at least 6 characters.
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148       The optional precision is a dot .  followed by  an  integer  indicating
149       how  many  digits follow the decimal point in the %f , %e , and %E con‐
150       versions. For instance, %.4f prints a float with 4 fractional digits.
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152       The integer in a width or precision can also be specified  as  *  ,  in
153       which  case  an  extra  integer argument is taken to specify the corre‐
154       sponding width or precision . This integer  argument  precedes  immedi‐
155       ately the argument to print.  For instance, %.*f prints a float with as
156       many fractional digits as the value of the argument  given  before  the
157       float.
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161       val printf : ('a, Pervasives.out_channel, unit) Pervasives.format -> 'a
162
163       Same as Printf.fprintf , but output on stdout .
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167       val  eprintf  : ('a, Pervasives.out_channel, unit) Pervasives.format ->
168       'a
169
170       Same as Printf.fprintf , but output on stderr .
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174       val sprintf : ('a, unit, string) Pervasives.format -> 'a
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176       Same as Printf.fprintf , but instead of printing on an output  channel,
177       return a string containing the result of formatting the arguments.
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181       val bprintf : Buffer.t -> ('a, Buffer.t, unit) Pervasives.format -> 'a
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183       Same  as Printf.fprintf , but instead of printing on an output channel,
184       append the formatted arguments to the given extensible buffer (see mod‐
185       ule Buffer ).
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189       val ifprintf : 'b -> ('a, 'b, 'c, unit) Pervasives.format4 -> 'a
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191       Same as Printf.fprintf , but does not print anything.  Useful to ignore
192       some material when conditionally printing.
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195       Since 3.10.0
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200       === Formatted output functions with continuations. ===
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203       val kfprintf : (Pervasives.out_channel -> 'd) -> Pervasives.out_channel
204       -> ('a, Pervasives.out_channel, unit, 'd) Pervasives.format4 -> 'a
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206       Same  as fprintf , but instead of returning immediately, passes the out
207       channel to its first argument at the end of printing.
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209
210       Since 3.09.0
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214       val ikfprintf : ('b -> 'd) -> 'b -> ('a, 'b, 'c, 'd) Pervasives.format4
215       -> 'a
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217       Same  as kfprintf above, but does not print anything.  Useful to ignore
218       some material when conditionally printing.
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220
221       Since 4.01.0
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225       val ksprintf : (string -> 'd) -> ('a, unit, string, 'd) Pervasives.for‐
226       mat4 -> 'a
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228       Same  as  sprintf above, but instead of returning the string, passes it
229       to the first argument.
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232       Since 3.09.0
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236       val kbprintf : (Buffer.t -> 'd) -> Buffer.t -> ('a, Buffer.t, unit, 'd)
237       Pervasives.format4 -> 'a
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239       Same as bprintf , but instead of returning immediately, passes the buf‐
240       fer to its first argument at the end of printing.
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242
243       Since 3.10.0
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247
248       === Deprecated ===
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251       val kprintf : (string -> 'b) -> ('a, unit, string, 'b)  Pervasives.for‐
252       mat4 -> 'a
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254       A deprecated synonym for ksprintf .
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2602018-04-14                          source:                          Printf(3)