Nyquist / XLISP 2.0 -
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ANSI C 'printf' Format
Nyquist/XLISP: The
*float-format* and
*integer-format*
variables define format strings for the underlying 'sprintf' C
function. In C, the same format string specification is
used for 'fprint' [writes to a file], 'printf' [writes to
standard output] and 'sprintf' [writes to another string]. These three
functions are meant in the following text with 'the printf functions'.
ANSI C: The printf functions write output under control of a
format string that specifies how subsequent arguments are converted for
output. If there are insufficient arguments for the format, the behavior is
undefined. If the format is exhausted while arguments remain, the excess
arguments are evaluated but are otherwise ignored. The printf functions
return when the end of the format string is encountered.
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Format String
The format string is composed of zero or more directives, which are
ordinary characters [except "%"], which are copied
unchanged to the output stream, and conversion specifications, each of which
results in fetching zero or more subsequent arguments. Each conversion
specification is introduced by the character "%":
%[flags][field-with][precision][data-type]conversion-type
After the "%", the following appear in sequence:
Flags - Zero or more flags that modify
the meaning of the conversion specification.
Field Width - An optional decimal integer
specifying a minimum field width. If the converted value has
fewer characters than the field width, it will be padded with spaces on the
left to the field width. The field is padded on the right if
the − flag has been
given, or padded with zeros if the
0 flag had been
given. A negative integer, given as 'field width'
argument, is interpreted as a
− flag followed by
a positive field width.
Precision - An optional decimal integer that
gives the minimum number of digits to appear for
integer conversions, the number of digits to appear
after the
decimal-point character for floating-point
e and
f conversions, or the
maximum number of significant digits for the floating-point
g conversion.
The precision takes the form of a period character followed by an
optional decimal integer:
.[integer]
If the integer is omitted, it is treated as zero, a
negative precision argument is taken as if it were missing.
Note: In C, the precision also specifies the
maximum number of characters to be written from a string in 's'
conversion, but "%s" should not be used in the XLISP
*float-format* or
*integer-format*
variables, otherwise XLISP will crash.
Data Type - An optional character specifying a
data type to be used for the
conversion.
XLISP: Nyquist/XLISP uses C 'long' signed integers
and C 'double' floats only, so with floating-point
numbers no special data type needs to
be given, while integer conversions should always be
prefixed by a 'l' [lowercase L], otherwise the printed
representation of integer numbers may be differently than the behaviour of
the Nyquist/XLISP functions.
Conversion Type - A character that specifies the
conversion type to be
applied.
Not with Nyquist/XLISP: In C, a 'field
width' or 'precision', or both, may be indicated by an asterisk *
instead of a digit string. In this case, an int argument supplies the field
width or precision. The arguments specifying field width or precision, or
both, shall appear [in that order] before the argument [if any] to be
converted.
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Flags
The flag characters and their meanings are:
− [minus sign character]
The result of the conversion will be left-justified
within the field.
+ [plus sign character]
The result of a signed conversion will always begin with a plus or
minus sign.
space [space character]
If the first character of a signed conversion is not a sign, or if a
signed conversion results in no characters, a space will be prepended to the
result. If the 'space' and
+ flags both appear, the
'space' flag will be ignored.
# [hash character]
The result is to be converted to an 'alternate form':
Octal Numbers - For o conversion, it increases the precision to force the
first digit of the result to be a zero.
Hexadecimal Numbers - For x or X conversion, a nonzero result will have
0x or 0X prepended to it.
Floating-point Numbers - For e, E, f, g, and G conversions, the result
will always contain a decimal-point character, even if no digits follow it
(normally, a decimal-point character appears in the result of these
conversions only if a digit follows it). For g and G conversions, trailing
zeros will not be removed from the result. For other conversions, the
behavior is undefined.
0 [number zero character]
For integer d, i, o, u, x, X, and floating-point e, E, f, g, G
conversions, leading zeros [following any indication of sign or base] are
used to pad to the field width.
No space padding is performed.
If the '0' and
− flags both
appear, the '0' flag will be ignored. For integer d, i, o, u,
x, X conversions, if a precision is specified,
the '0' flag will be ignored. For other
conversions, the behavior is undefined.
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Data Type
h [lowercase H character]
A following d, i, o, u, x, or X conversion specifier applies to a
short int or unsigned short int argument [the argument will have been
promoted according to the integral promotions, and its value shall be
converted to short int or unsigned short int before printing].
A following n conversion specifier applies to a pointer to a short int
argument.
l [lowercase L character]
A following d, i, o, u, x, or X conversion specifier applies to a
long int or unsigned long int argument.
A following n conversion specifier applies to a pointer to a long int
argument.
L [uppercase L character]
A following e, E, f, g, or G conversion specifier applies to a long
double argument.
If an h, l, or L appears with any other conversion specifier, the
behavior is undefined.
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Conversion Type
Integer conversion:
d, i, o, u, x,
X
The integer argument is converted to:
|
d |
→ |
signed decimal |
|
i |
→ |
signed decimal |
|
o |
→ |
unsigned octal |
|
u |
→ |
unsigned decimal |
|
x |
→ |
unsigned hexadecimal, using 'abcdef' |
|
X |
→ |
unsigned hexadecimal, using 'ABCDEF' |
The precision specifies the minimum number
of digits to appear. If the value being converted can be
represented in fewer digits, it will be expanded with leading zeros. The
default precision is 1. The result of converting a zero value
with an explicit precision of zero results in no characters.
XLISP: Nyquist/XLISP uses C 'long' signed integers, so
the integer conversions should always be prefixed by a 'l' [lowercase
L] indicating a 'long int' C
data type, otherwise the printed
representation of integer numbers may be differently than the behaviour of
the Nyquist/XLISP functions.
Floating-point conversion:
f
The floating-point argument of C data type
'double' is converted to decimal notation in the style:
[-]ddd.ddd
where the number of digits after the decimal-point character
is equal to the precision specification.
If the precision is missing, it is
taken as 6. If the
precision is explicitly zero, no
decimal-point character appears. If a
decimal-point character appears, at least one digit appears
before it. The value is rounded to the appropriate
number of digits.
e, E
The floating-point argument of C data type
'double' is converted in the style:
[-]d.ddde+-dd
where there is one digit before the decimal-point character
[which is nonzero if the argument is nonzero] and the number of digits after
it is equal to the precision. If
the precision is missing, it is taken
as 6. If the
precision is zero, no
decimal-point character appears. The value is
rounded to the appropriate number of digits. The exponent
always contains at least two digits. If the value is zero, the
exponent is zero. The "E" conversion specifier will
produce a number with 'E' instead of 'e' introducing the exponent.
g, G
The floating-point argument of C data type
'double' is converted in style f or
e or in style
E in the case of a "G"
conversion specifier, with the precision
specifying the number of significant digits. If an explicit
precision is zero, it is taken as
1. The style used depends on the value converted.
Style e will be used only if
the exponent resulting from such a conversion is less than -4
or greater than or equal to the precision.
Trailing zeros are removed from the fractional portion of the result.
A decimal-point character appears only if it is followed by
a digit.
Other conversion types defined in ANSI C, but not to
be used with the XLISP
*float-format* and
*integer-format*
variables, because XLISP will produce nonsense or just simply will crash:
c
The integer argument is converted to an 'unsigned char',
and the resulting character is written.
XLISP: If the
*float-format* or
*integer-format*
variable is set to "%c", then with integers or
floating-point numbers, the lowest 8 bit of the
internal binary representation will be interpreted as an
ASCII character.
s
The argument shall be a pointer to an array of character type.
Characters from the array are written up to [but not including] a
terminating null character. If the
precision is specified, no more than that many
characters are written. If the
precision is not specified or is greater than
the size of the array, the array shall contain a null character.
XLISP: If
p
The argument shall be a pointer to 'void'. The value of the pointer
is converted to a sequence of printable characters, in an
implementation-defined manner.
n
The argument shall be a pointer to an integer into which is written
the number of characters written to the output stream so far by this call to
the C 'fprintf' function. No argument is
converted.
%
A "%" is written. No argument is
converted. The complete conversion specification shall be
"%%".
If a conversion specification is invalid, the behavior is undefined.
In no case does a nonexistent or small
field width cause truncation of a
field. If the result of a conversion is wider than the
field width, the field is expanded
to contain the conversion result.
The minimum value for the maximum number of characters produced by
any single conversion shall be 509.
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Nyquist / XLISP 2.0 -
Contents |
Tutorials |
Examples |
Reference