Module Printf

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 one argument.

Conversion specifications consist in the % character, followed by optional flags and field widths, followed by one or two conversion character. The conversion characters and their meanings are:

• d, i, n, 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 in Caml syntax (dddd.ddd with a mandatory .).
• 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 therefore 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.
• !: take no argument and flush the output.
• %: take no argument and output one % character.

The optional flags include:

• -: 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 field widths are composed of an optional integer literal indicating the minimal width of the result, possibly followed by a dot . and another integer literal indicating how many digits follow the decimal point in the %f, %e, and %E conversions. For instance, %6d prints an integer, prefixing it with spaces to fill at least 6 characters; and %.4f prints a float with 4 fractional digits. Each or both of the integer literals can also be specified as a *, in which case an extra integer argument is taken to specify the corresponding width or precision.

Warning: if too few arguments are provided, for instance because the printf function is partially applied, the format is immediately printed up to the conversion of the first missing argument; printing will then resume when the missing arguments are provided. For example, List.iter (printf "x=%d y=%d " 1) [2;3] prints x=1 y=2 3 instead of the expected x=1 y=2 x=1 y=3. To get the expected behavior, do List.iter (fun y -> printf "x=%d y=%d " 1 y) [2;3].

Same as Printf.fprintf, but output on stdout.

Same as Printf.fprintf, but output on stderr.

Same as Printf.fprintf, but instead of printing on an output channel, return a string containing the result of formatting the arguments.

Same as Printf.fprintf, but instead of printing on an output channel, append the formatted arguments to the given extensible buffer (see module Buffer).

kprintf k format arguments is the same as sprintf format arguments, except that the resulting string is passed as argument to k; the result of k is then returned as the result of kprintf.