m4: Format
11.7 Formatting strings (printf-like)
=====================================
Formatted output can be made with 'format':
-- Builtin: format (FORMAT-STRING, ...)
Works much like the C function 'printf'. The first argument
FORMAT-STRING can contain '%' specifications which are satisfied by
additional arguments, and the expansion of 'format' is the
formatted string.
The macro 'format' is recognized only with parameters.
Its use is best described by a few examples:
define(`foo', `The brown fox jumped over the lazy dog')
=>
format(`The string "%s" uses %d characters', foo, len(foo))
=>The string "The brown fox jumped over the lazy dog" uses 38 characters
format(`%*.*d', `-1', `-1', `1')
=>1
format(`%.0f', `56789.9876')
=>56790
len(format(`%-*X', `5000', `1'))
=>5000
ifelse(format(`%010F', `infinity'), ` INF', `success',
format(`%010F', `infinity'), ` INFINITY', `success',
format(`%010F', `infinity'))
=>success
ifelse(format(`%.1A', `1.999'), `0X1.0P+1', `success',
format(`%.1A', `1.999'), `0X2.0P+0', `success',
format(`%.1A', `1.999'))
=>success
format(`%g', `0xa.P+1')
=>20
Using the 'forloop' macro defined earlier (⇒Forloop), this
example shows how 'format' can be used to produce tabular output.
$ m4 -I examples
include(`forloop.m4')
=>
forloop(`i', `1', `10', `format(`%6d squared is %10d
', i, eval(i**2))')
=> 1 squared is 1
=> 2 squared is 4
=> 3 squared is 9
=> 4 squared is 16
=> 5 squared is 25
=> 6 squared is 36
=> 7 squared is 49
=> 8 squared is 64
=> 9 squared is 81
=> 10 squared is 100
=>
The builtin 'format' is modeled after the ANSI C 'printf' function,
and supports these '%' specifiers: 'c', 's', 'd', 'o', 'x', 'X', 'u',
'a', 'A', 'e', 'E', 'f', 'F', 'g', 'G', and '%'; it supports field
widths and precisions, and the flags '+', '-', ' ', '0', '#', and '''.
For integer specifiers, the width modifiers 'hh', 'h', and 'l' are
recognized, and for floating point specifiers, the width modifier 'l' is
recognized. Items not yet supported include positional arguments, the
'n', 'p', 'S', and 'C' specifiers, the 'z', 't', 'j', 'L' and 'll'
modifiers, and any platform extensions available in the native 'printf'.
For more details on the functioning of 'printf', see the C Library
Manual, or the POSIX specification (for example, '%a' is supported even
on platforms that haven't yet implemented C99 hexadecimal floating point
output natively).
Unrecognized specifiers result in a warning. It is anticipated that
a future release of GNU 'm4' will support more specifiers, and give
better warnings when various problems such as overflow are encountered.
Likewise, escape sequences are not yet recognized.
format(`%p', `0')
error->m4:stdin:1: Warning: unrecognized specifier in `%p'
=>
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