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).B: convert a boolean argument to the string true or falseb: 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 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.