| Printf(3o) | OCamldoc | Printf(3o) |
Printf - Formatted output functions.
Module Printf
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 4.01.0
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 .
| source: | 2019-01-25 |