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:

% [positional specifier] [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 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 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 fmt.
• !: take no argument and flush the output.
• %: take no argument and output one % character.

The optional positional specifier consists of an integer followed by a $; the integer indicates which argument to use, the first argument being denoted by 1.

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, unless an optional positional specifier is given to indicates which argument to use. For instance, %.*3$f prints a float with as many fractional digits as the value of the third argument.

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 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.

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.

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

A deprecated synonym for ksprintf.