Author(s): The CLIP Group.
Version: 1.10#7 (2006/4/26, 19:22:13 CEST)
Version of last change: 1.9#212 (2003/12/21, 2:18:19 CET)
The format
family of predicates is due to Quintus Prolog. They act as a Prolog interface to the C stdio
function printf()
, allowing formatted output.
Output is formatted according to an output pattern which can have either a format control sequence or any other character, which will appear verbatim in the output. Control sequences act as place-holders for the actual terms that will be output. Thus
?- format("Hello ~q!",world).
will print Hello world!
.
If there is only one item to print it may be supplied alone. If there are more they have to be given as a list. If there are none then an empty list should be supplied. There has to be as many items as control characters.
The character ~
introduces a control sequence. To print a ~
verbatim just repeat it:
?- format("Hello ~~world!", []).
will result in Hello ~world!
.
A format may be spread over several lines. The control sequence \c
followed by a LFD will translate to the empty string:
?- format("Hello \c world!", []).
will result in Hello world!
.
format
)format
)
General properties: format(C, A)
format(C,A)
.
(basic_props:native/2
)
Usage: format(Format, Arguments)
Arguments
onto current output stream according to format Format
.
Format
is an atom or string describing how the arguments should be formatted. If it is an atom it will be converted into a string with name/2
.
(format:format_control/1
)
General properties: format(S, C, A)
format(S,C,A)
.
(basic_props:native/2
)
Usage: format(+Stream, Format, Arguments)
Arguments
onto Stream
according to format Format
.
Format
is an atom or string describing how the arguments should be formatted. If it is an atom it will be converted into a string with name/2
.
(format:format_control/1
)
The general format of a control sequence is ~
. The character N
C
C
determines the type of the control sequence. N
is an optional numeric argument. An alternative form of N
is *
. *
implies that the next argument in Arguments
should be used as a numeric argument in the control sequence. Example:
?- format("Hello~4cworld!", [0'x]).
and
?- format("Hello~*cworld!", [4,0'x]).
both produce
Helloxxxxworld!
The following control sequences are available.
N
c (Print character.) The argument is a number that will be interpreted as an ASCII code. N
defaults to one and is interpreted as the number of times to print the character.
N
e
N
E
N
f
N
g
N
G (Print float). The argument is a float. The float and N
will be passed to the C printf()
function as
printf("%.IfN
e",Arg
) printf("%.N
E",Arg
) printf("%.N
f",Arg
) printf("%.N
g",Arg
) printf("%.N
G",Arg
)
N
is not supplied the action defaults to
printf("%e",Arg
) printf("%E",Arg
) printf("%f",Arg
) printf("%g",Arg
) printf("%G",Arg
)
N
d (Print decimal.) The argument is an integer. N
is interpreted as the number of digits after the decimal point. If N
is 0 or missing, no decimal point will be printed. Example:
?- format("Hello ~1d world!", [42]). ?- format("Hello ~d world!", [42]).will print as
Hello 4.2 world! Hello 42 world!respectively.
N
D (Print decimal.) The argument is an integer. Identical to ~N
d
except that ,
will separate groups of three digits to the left of the decimal point. Example:
?- format("Hello ~1D world!", [12345]).will print as
Hello 1,234.5 world!
N
r (Print radix.) The argument is an integer. N
is interpreted as a radix. N
should be >= 2 and <= 36. If N
is missing the radix defaults to 8. The letters a-z
will denote digits larger than 9. Example:
?- format("Hello ~2r world!", [15]). ?- format("Hello ~16r world!", [15]).will print as
Hello 1111 world! Hello f world!respectively.
N
R (Print radix.) The argument is an integer. Identical to ~N
r
except that the letters A-Z
will denote digits larger than 9. Example:
?- format("Hello ~16R world!", [15]).will print as
Hello F world!
N
s (Print string.) The argument is a list of ASCII codes. Exactly N
characters will be printed. N
defaults to the length of the string. Example:
?- format("Hello ~4s ~4s!", ["new","world"]). ?- format("Hello ~s world!", ["new"]).will print as
Hello new worl! Hello new world!respectively.
?- format("Hello ~i~s world!", ["old","new"]).will print as
Hello new world!
write_canonical/2
(section Term output). Example:
?- format("Hello ~k world!", [[a,b,c]]).will print as
Hello .(a,.(b,.(c,[]))) world!
print/2
(section Term output). Example:
suposing the user has defined the predicate
:- multifile portray/1. portray([X|Y]) :- print(cons(X,Y)).then
?- format("Hello ~p world!", [[a,b,c]]).will print as
Hello cons(a,cons(b,cons(c,[]))) world!
writeq/2
(section Term output). Example:
?- format("Hello ~q world!", [['A','B']]).will print as
Hello ['A','B'] world!
write/2
(section Term output). Example:
?- format("Hello ~w world!", [['A','B']]).will print as
Hello [A,B] world!
N
n (Print newline.) Print N
newlines. N
defaults to 1. Example:
?- format("Hello ~n world!", []).will print as
Hello world!
~
The following control sequences are also available for compatibility, but do not perform any useful functions.
N
| (Set tab.) Set a tab stop at position N
, where N
defaults to the current position, and advance the current position there.
N
+ (Advance tab.) Set a tab stop at N
positions past the current position, where N
defaults to 8, and advance the current position there.
N
t (Set fill character.) Set the fill character to be used in the next position movement to N
, where N
defaults to SPC.
Usage: format_control(C)
C
is an atom or string describing how the arguments should be formatted. If it is an atom it will be converted into a string with name/2
.
format_control(C)
may not conform the functionality documented.
(doc_props:doc_incomplete/1
)
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