Module Printf

module Printf: sig .. end

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 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, n, l, L, or N: convert an integer argument to signed decimal.
• u: convert an integer argument to unsigned decimal.
• 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: insert a string argument in Caml syntax (double quotes, escapes).
• c: insert a character argument.
• C: insert a character argument in Caml 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 Caml 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).
• B: convert a boolean argument to the string true or false
• b: convert a boolean argument (for backward compatibility; 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. Takes two arguments and applies 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 takes only one argument (with type out_channel -> unit) and apply it to outchan.
• { fmt %}: convert a format string argument. The argument must have the same type as the internal format string fmt.
• ( fmt %): format string substitution. Takes a format string argument and substitutes 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.
• ,: the 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 numerical conversions, prefix number with a + sign if positive.
• space: for numerical conversions, prefix number with a space if positive.
• #: request an alternate formatting style for numbers.

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, 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 ifprintf : 'a -> ('b, 'a, unit) format -> 'b

Same as Printf.fprintf, but does not print anything. Useful to ignore some material when conditionally printing.
Since 3.10.0

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 kfprintf : (out_channel -> 'a) ->
       out_channel ->
       ('b, out_channel, unit, 'a) format4 -> 'b

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

Same as sprintf above, but instead of returning the string, passes it to the first argument.
Since 3.09.0

val kbprintf : (Buffer.t -> 'a) ->
       Buffer.t -> ('b, Buffer.t, unit, 'a) format4 -> 'b

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

A deprecated synonym for ksprintf.