@cindex numeric prefix
@cindex field width
@cindex padding
- All the specification characters allow an optional numeric prefix
-between the @samp{%} and the character. The optional numeric prefix
-defines the minimum width for the object. If the printed
-representation of the object contains fewer characters than this, then
-it is padded. The padding is on the left if the prefix is positive
-(or starts with zero) and on the right if the prefix is negative. The
-padding character is normally a space, but if the numeric prefix
-starts with a zero, zeros are used for padding. Some of these
-conventions are ignored for specification characters for which they do
-not make sense. That is, %s, %S and %c accept a numeric prefix
+ All the specification characters allow an optional ``width'', which
+is a digit-string between the @samp{%} and the character. If the
+printed representation of the object contains fewer characters than
+this width, then it is padded. The padding is on the left if the
+prefix is positive (or starts with zero) and on the right if the
+prefix is negative. The padding character is normally a space, but if
+the width starts with a zero, zeros are used for padding. Some of
+these conventions are ignored for specification characters for which
+they do not make sense. That is, %s, %S and %c accept a width
starting with 0, but still pad with @emph{spaces} on the left. Also,
-%% accepts a numeric prefix, but ignores it. Here are some examples
-of padding:
+%% accepts a width, but ignores it. Here are some examples of
+padding:
@example
(format "%06d is padded on the left with zeros" 123)
@result{} "123 is padded on the right"
@end example
- @code{format} never truncates an object's printed representation, no
-matter what width you specify. Thus, you can use a numeric prefix to
-specify a minimum spacing between columns with no risk of losing
-information.
+If the width is too small, @code{format} does not truncate the
+object's printed representation. Thus, you can use a width to specify
+a minimum spacing between columns with no risk of losing information.
In the following three examples, @samp{%7s} specifies a minimum width
of 7. In the first case, the string inserted in place of @samp{%7s} has
@end group
@end smallexample
+ All the specification characters allow an optional ``precision''
+before the character (after the width, if present). The precision is
+a decimal-point @samp{.} followed by a digit-string. For the
+floating-point specifications (%e, %f, %g), the precision specifies
+how many decimal places to show; if zero, the decimal-point itself is
+also omitted. For %s and %S, the precision truncates the string to
+the given width, so @code{"%.3s"} shows only the first three
+characters of the representation for @var{object}. Precision is
+ignored for other specification characters.
+
+Immediately after the % and before the optional width and precision,
+you can put certain ``flag'' characters.
+
+A space @var{" "} inserts a space for positive numbers (otherwise
+nothing is inserted for positive numbers). This flag is ignored
+except for %d, %e, %f, %g.
+
+The flag @var{"#"} indicates ``alternate form''. For %o it ensures
+that the result begins with a 0. For %x and %X the result is prefixed
+with ``0x'' or ``0X''. For %e, %f, and %g a decimal point is always
+shown even if the precision is zero.
+
@node Case Conversion
@comment node-name, next, previous, up
@section Case Conversion in Lisp
The argument used for %d, %o, %x, %e, %f, %g or %c must be a number.
Use %% to put a single % into the output.
+The basic structure of a %-sequence is
+ % <flags> <width> <precision> character
+where flags is [- #0]+, width is [0-9]+, and precision is .[0-9]+
+
usage: (format STRING &rest OBJECTS) */)
(nargs, args)
int nargs;
where
- flags ::= [#-* 0]+
+ flags ::= [- #0]+
field-width ::= [0-9]+
precision ::= '.' [0-9]*
digits to print after the '.' for floats, or the max.
number of chars to print from a string. */
- /* NOTE the handling of specifiers here differs in some ways
- from the libc model. There are bugs in this code that lead
- to incorrect formatting when flags recognized by C but
- neither parsed nor rejected here are used. Further
- revisions will be made soon. */
-
- /* incorrect list of flags to skip; will be fixed */
- while (index ("-*# 0", *format))
+ while (index ("-0# ", *format))
++format;
if (*format >= '0' && *format <= '9')
if (*format == 'c')
{
if (! SINGLE_BYTE_CHAR_P (XINT (args[n]))
- /* Note: No one can remeber why we have to treat
+ /* Note: No one can remember why we have to treat
the character 0 as a multibyte character here.
But, until it causes a real problem, let's
don't change it. */
discarded[format - format_start] = 1;
format++;
- /* Process a numeric arg and skip it. */
- /* NOTE atoi is the wrong thing to use here; will be fixed */
+ while (index("-0# ", *format))
+ {
+ if (*format == '-')
+ {
+ negative = 1;
+ }
+ discarded[format - format_start] = 1;
+ ++format;
+ }
+
minlen = atoi (format);
- if (minlen < 0)
- minlen = - minlen, negative = 1;
-
- /* NOTE the parsing here is not consistent with the first
- pass, and neither attempt is what we want to do. Will be
- fixed. */
- while ((*format >= '0' && *format <= '9')
- || *format == '-' || *format == ' ' || *format == '.')
+
+ while ((*format >= '0' && *format <= '9') || *format == '.')
{
discarded[format - format_start] = 1;
format++;
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