Printf(3)

NAME
Printf - Formatted output functions.

Module
Module Printf

Documentation

Module Printf
 : sig end

Formatted output functions.

val fprintf : out_channel -> ('a, out_channel, unit) 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. The flag # adds underscores to large values for readability.

- 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 . The flag # adds underscores to large values for readability.

- x : convert an integer argument to unsigned hexadecimal, using lowercase letters. The flag # adds a 0x prefix to non zero values.

- X : convert an integer argument to unsigned hexadecimal, using uppercase letters. The flag # adds a 0X prefix to non zero values.

- o : convert an integer argument to unsigned octal. The flag # adds a 0 prefix to non zero values.

- 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 ). Converts to hexadecimal with the # flag (see h ).

- 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). 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.

- h or H : convert a floating-point argument to hexadecimal notation, in the style 0xh.hhhh p+-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 integer types and the floating-point type F . 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 , %E , %h , and %H conversions or the maximum number of significant digits to appear for the %F , %g and %G 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, out_channel, unit) format -> 'a

Same as Printf.fprintf , but output on stdout .

val eprintf : ('a, out_channel, unit) format -> 'a

Same as Printf.fprintf , but output on stderr .

val sprintf : ('a, unit, string) 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) 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) format4 -> 'a

Same as Printf.fprintf , but does not print anything. Useful to ignore some material when conditionally printing.

Since 3.10.0

val ibprintf : Buffer.t -> ('a, Buffer.t, unit) format -> 'a

Same as Printf.bprintf , but does not print anything. Useful to ignore some material when conditionally printing.

Since 4.11.0

Formatted output functions with continuations.

val kfprintf : (out_channel -> 'd) -> out_channel -> ('a, out_channel, unit, 'd) 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) 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) 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) 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

val ikbprintf : (Buffer.t -> 'd) -> Buffer.t -> ('a, Buffer.t, unit, 'd) format4 -> 'a

Same as kbprintf above, but does not print anything. Useful to ignore some material when conditionally printing.

Since 4.11.0

Deprecated

val kprintf : (string -> 'b) -> ('a, unit, string, 'b) format4 -> 'a

A deprecated synonym for ksprintf .