SYS-PRINT(2)SYS-PRINT(2)NAME
print, aprint, fprint, sprint - print formatted output
SYNOPSIS
include "sys.m";
sys := load Sys Sys->PATH;
aprint: fn(format: string, *): array of byte;
fprint: fn(fd: ref FD, format: string, *): int;
print: fn(format: string, *): int;
sprint: fn(format: string, *): string;
DESCRIPTION
These functions format and print their arguments as UTF text. Print
writes text to the standard output. Fprint writes to the named output
file descriptor. Sprint places text in a string, which it returns.
Aprint is similar but returns the text in utf(6) representation as an
array of bytes. Print and fprint return the number of bytes transmit‐
ted or a negative value if an error was encountered when writing the
output.
Each of these functions converts, formats, and prints its trailing
arguments under control of a format string. The format contains two
types of objects: plain characters, which are simply copied to the out‐
put stream, and conversion specifications, each of which results in
fetching of zero or more arguments. The Limbo compiler recognizes
calls to these functions and checks that the arguments match the format
specifications in number and type.
Each conversion specification has the following format:
% [flags] verb
The verb is a single character and each flag is a single character or a
(decimal) numeric string. Up to two numeric strings may be used; the
first is called f1, the second f2. They can be separated by `.', and
if one is present, then f1 and f2 are taken to be zero if missing, oth‐
erwise they are considered `omitted'. Either or both of the numbers
may be replaced with the character *, meaning that the actual number
will be obtained from the argument list as an integer. The flags and
numbers are arguments to the verb described below.
d, o, x, X
The numeric verbs d, o, and x format their int arguments in dec‐
imal, octal, and hexadecimal (with hex digits in lower-case).
The flag b is required when the corresponding value is a Limbo
big, not an int. Arguments are taken to be signed, unless the u
flag is given, to force them to be treated as unsigned. Each
interprets the flags - , , , and # to mean left justified, com‐
mas every three digits, and alternative format. If f2 is not
omitted, the number is padded on the left with zeros until at
least f2 digits appear. Then, if alternative format is speci‐
fied for x conversion, the number is preceded by 0x. Finally,
if f1 is not omitted, the number is padded on the left (or
right, if left justification is specified) with enough blanks to
make the field at least f1 characters long. The verb X is simi‐
lar to x, except that the hexadecimal digits are displayed in
upper-case, and in alternative format, the number is preceded by
0X.
e, f, g
The floating point verbs e, f, and g take a real argument. Each
interprets the flags +, -, and # to mean always print a sign,
left justified, and alternative format. F1 is the minimum field
width and, if the converted value takes up less than f1 charac‐
ters, it is padded on the left (or right, if `left justified')
with spaces. F2 is the number of digits that are converted
after the decimal place for e and f conversions, and f2 is the
maximum number of significant digits for g conversions. The f
verb produces output of the form [-]digits[.digits]. The e con‐
version appends an exponent e[-]digits. The g verb will output
the argument in either e or f with the goal of producing the
smallest output. Also, trailing zeros are omitted from the
fraction part of the output, and a trailing decimal point
appears only if it is followed by a digit. When alternative
format is specified, the result will always contain a decimal
point, and for g conversions, trailing zeros are not removed.
E, G These are the same as e and g respectively, but use E not e to
specify an exponent when one appears.
c The c verb converts a single Unicode character from an int argu‐
ment to a UTF encoding, justified within a field of f1 charac‐
ters as described above.
r The r verb takes no arguments; it prints the error string asso‐
ciated with the most recent system error.
s The s verb copies a string to the output. The number of charac‐
ters copied (n) is the minimum of the size of the string and f2.
These n characters are justified within a field of f1 characters
as described above.
q The q verb copies a string to the output as for s, but quotes
the string in the style of sh(1) only if necessary to avoid
ambiguity (for instance if the string contains quotes or spa‐
ces). If the format string, however, includes the specifier #
(for example %#q), the printed string will always be quoted.
SOURCE
/libinterp/runt.c:/^xprint
/os/port/print.c
/lib9/print.c
SEE ALSOsys-intro(2), sys-open(2)BUGS
The x verb does not apply the 0x prefix when f2 is present. The prefix
should probably be 16r anyway.
SYS-PRINT(2)
