printf(+Stream, +Format, ?ArgList)

+Stream

Integer (stream number) or Atom (reserved or user-defined symbolic stream name).

+Format

String or Atom.

+ArgList

List or any Term.

Description

%AC or %NC

where C is a single letter format control option and A or N are optional parameters. Any characters that are not part of a control sequence are written to the output stream Stream.

A

A may consist of: a minus sign, a plus sign, a space , the character '#', a digit string (or a '*'), a period, a digit string (or a '*') and a length modifier 'l'.

This substring A is interpreted in the same way as in the 'C' routine printf(3).

N

The argument N has to be a non-negative integer.

ArgList is a list of arguments which will be interpreted and possibly printed by format control options. If there is only one argument, it need not be in a list.

The elements from the argument list ArgList are interpreted according to the following control options and printed to the output stream Stream. The arguments must be of the type specified, or the corresponding event will be raised.

%a

The argument has to be an atom and is passed to write/1.

%A

The argument has to be an atom. All its characters are converted to upper case and the result is printed.

%Nc

The argument has to be a numeric ASCII code and is printed N times. If N is omitted, it defaults to 1.

%Ad

The argument has to be an integer and is printed according to the substring A in signed decimal notation.

%Ao

The argument has to be an integer and is printed according to the substring A in unsigned octal notation.

%Au

The argument has to be an integer and is printed according to the substring A in unsigned decimal notation.

%Ax

The argument has to be an integer and is printed according to the substring A in unsigned hexadecimal notation. (The letters abcdef are used.)

%AX

The argument has to be an integer and is printed according to the substring A in unsigned hexadecimal notation. (The letters ABCDEF are used.)

%Ae

The argument has to be a floating-point number and is printed according to the substring A in exponential notation.('e' is used for exponentiation)

%AE

The argument has to be a floating-point number and is printed according to the substring A in exponential notation. ('E' is used for exponentiation)

%Af

The argument has to be a floating-point number and is printed according to the substring A in non-exponential form.

%Ag

The argument has to be a floating-point number and is printed according to the substring A in exponential or non-exponential form, whichever gives the best precision in minimum space.('e' is used for exponentiation)

%As

The argument has to be a string or an atom and is printed according to the substring A.

%Nr

The argument has to be an integer and it is printed as signed in radix N using the digits 0-9 and letters a-z. N must be greater than 1 and less than 37. If N is not specified, it defaults to 8.

%NR

The argument has to be an integer and it is printed as signed in radix N using the digits 0-9 and letters A-Z. N must be greater than 1 and less than 37. If N is not specified, it defaults to 8.

The following control options can interpret arguments of any type.

%Ni

N arguments are ignored. If N is omitted, it defaults to 1.

%k

The argument is passed to display/1. It is a synonym for %O.w.

%p

The argument is passed to print/1. It is a synonym for %Pw.

%q

%q

The argument is passed to writeq/1. It is a synonym for %QDvw.

%w

The argument is by default passed to write/1. However, the %w format recognises a number of control characters, placed between the percent sign and w. They give the user full control over the various possibilities of printing Prolog terms. A number immediately after the percent sign determines the depth to which the term is printed, if an asterisk is used instead, the depth is taken from the next argument in ArgList. The default depth is determined by the setting of the (stream-specific or global) print_depth flag. After the optional depth, the following modifiers are recognized:

O

omit operator declarations. All terms are written in the canonical notation without operators.

Q

quote atoms and strings if necessary.

.

write lists in the dot functor notation rather than using the square bracket notation, e.g. .(1, .(2, [])) rather than [1, 2].

G

print the term as a goal, i.e. goal write macros will be taken into account.

P

call the user-defined predicate portray/1, 2 in the way print/1, 2 does.

D

disregard the depth restriction of the print-depth flag and print the whole term.

U

call portray/1, 2 even on variables. This is to be used in conjunction with the P option. Note that metaterms are always portrayed.

V

print the full variable name, if available, either in the form Name_Number, e.g. Alpha_132, or Name#Number, if the variable had been given a name via lib(var_name). This is necessary to distinguish different variables with the same name.

v

print only the short variable form, i.e. even when available, the variable name is not printed. This is useful if a term should be written and read back in several times. If neither V nor v is specified, variables are printed only with their name, if it is available. Variable without names are always printed in the v form.

_

print every variable as a simple underscore. Any information about multiple occurrences of a variable is lost with this format. It is mainly useful to produce output that can be compared easily with the output of a different Eclipse session.

I

any term of the form '$VAR'(N), where N is a non-negative integer, is printed as a variable name consisting of a capital letter followed by a number. The capital letter is the ((N mod 26)+1)st letter of the alphabet, and the integer is N//26. If N is an atom, this atom gets printed instead of the term.

M

print the full contents of all metaterm attributes. This is necessary if the term is to be written out and read back in.

m

metaterm attributes are printed using the corresponding print handlers. If neither M nor m is specified, metaterms are printed as variables, without any attribute.

N

print newline (NL) characters as newlines rather than as an escape sequence, even when they occur in quoted atoms or strings. This only makes sense together with the Q modifier.

T

do not apply any write macros.

C

print the term as a clause, i.e. clause macros will be taken into account.

%W

Like %w, but the stream's default output options are taken into account, unless overridden by the format options specified here. Note in particular that a default setting may be cancelled by prefixing the format character with a minus sign. E.g. if the stream defaults specify that quotes should be printed (quoted(true)), this can be overridden by a %-QW format string.

%%

One % is printed.

%Nn

N newline sequences are printed. If N is omitted it defaults to 1. Which newline characters are printed depends on the setting of the stream's end_of_line property. If the stream's flush-property is set to end_of_line, the stream is also flushed.

%Nt

N tab characters are printed. If N is omitted it defaults to 1.

%b

The output buffer is flushed, the data is written into the file.

Fail Conditions

Resatisfiable

Exceptions

(4) instantiation fault

Stream is not instantiated.

(5) type error

Stream is not an atom or an integer.

(5) type error

Format is not an atom or a string.

(5) type error

ArgList contains argument whose type does not correspond to the control sequence.

(7) string contains unexpected characters

Format is not correct, it contains too many asterisks or a control character is missing or there is a redundant character before the control character.

(8) bad argument list

ArgList has not enough arguments.

(192) illegal stream mode

Stream is not an output stream.

(193) illegal stream specification

Stream is not a stream specification.

Examples

Success:
[eclipse]: printf(output, "abc %s ghi %+*.*E...",
        ["def", 2, 3, 12.34]).
abc def ghi +1.234E+01...
yes.
[eclipse]: printf(output, "abc %12c %*n", [77, 3]).
abc MMMMMMMMMMMM



yes.
[eclipse]: printf(output, "abc %i def %a%2t%%", [123, ghi]).
abc  def ghi            %
yes.
[eclipse]: printf(output, "%w", ['A'+'B']).
A + B
yes.
[eclipse]: printf(output, "%q", ['A'+'B']).
'A' + 'B'
yes.
[eclipse]: printf(output, "%k", ['A'+'B']).
+(A, B)
yes.

Error:
      printf(S, "%s", ["eclipse"]).          (Error 4).
      printf(output, F, eclipse).            (Error 4).
      printf("output", "%s", ["eclipse"]).   (Error 5).
      printf(output, "%a", 1).               (Error 5).
      printf(output, "%*.*.*s", [2, 3, 4,  "eclipse"]).
                                             (Error 7).
      printf(output, "%d %d %d", [1, 9]).    (Error 8).
      printf(9, "%s", ["eclipse"]).
                       (Error 192). % stream not open
      printf(atom, "%s", ["eclipse"]).       (Error 193).
      printf(s, comment%s, eclipse).
                                 '%' starts a comment

See Also