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calc/help/printf
Landon Curt Noll 7eba99ac29 Add notes about unexpeded things in using calc
2021-03-06 22:12:14 -08:00

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NAME
printf - formatted print to standard output
SYNOPSIS
printf(fmt, x_1, x_2, ...)
TYPES
fmt string
x_1, x_2, ... any
return null
DESCRIPTION
The function printf() is similar to the C function with the same name.
The most significant difference is that there is no requirement
that the types of values of the arguments x_i match the
corresponding format specifier in fmt. Thus, whatever the
format specifier, a number is printed as a number, a string as
a string, a list as a list, a matrix as a matrix, an xx-object
as an xx-object, etc.
Except when a '%' is encountered, characters of the string fmt are
printed in succession to the standard output. Occurrence of
a '%' indicates the intention to build a format specifier.
This is completed by a succession of characters as follows:
an optional '-'
zero or more decimal digits
an optional '. followed by zero or more decimal digits
an optional 'l'
one of the letters: d, s, c, f, e, g, r, o, x, b,
If any other character is read, the '%' and any characters
between '%' and the character are ignored and no specifier is
formed. E.g. "%+f" prints as if only "f" were read; "% 10s"
prints as "10s", "%X" prints as "X", "%%" prints as "%".
The characters in a format specifier are interpreted as follows:
a minus sign sets the right-pad flag;
the first group of digits determines the width w;
w = 0 if there are no digits
a dot indicates the precision is to be read from the
following digits; if there is no dot,
precision = config("display").
any digits following the . determines the precision p;
p = 0 if there are no digits
any 'l' before the final letter is ignored
the final letter determines the mode as follows:
d, s, c current config("mode")
f real (decimal, floating point)
e exponential
g general format (real or exponential)
r fractional
o octal
x hexadecimal
b binary
If the number of arguments after fmt is less than the number
of format specifiers in fmt, the "missing" arguments may be
taken to be null values - these contribute nothing to the output;
if a positive width w has been specified, the effect is to
produce w spaces, e.g., printf("abc%6dxyz") prints "abc xyz".
Control charters may be given in fmt by escaping them with
the \ character. The following control charter escape
sequences are recognized:
\a audible bell byte 0x07 in ASCII encoding
\b backspace byte 0x08 in ASCII encoding
\f form feed byte 0x0c in ASCII encoding
\n newline byte 0x0b in ASCII encoding
\r return byte 0x0a in ASCII encoding
\t tab byte 0x0d in ASCII encoding
\v vertical tab byte 0x09 in ASCII encoding
If i <= the number of specifiers in fmt, the value of argument
x_i is printed in the format specified by the i-th specifier.
If a positive width w has been specified and normal printing
of x_i does not include a '\n' character, what is printed will
if necessary be padded with spaces so that the length of the
printed output is at least the w. Note that control characters
(e.g., '\a', '\b', '\f', '\n', '\r', '\t', '\n') count as one
character. If the 'right-pad' flag has been set, the padding
is on the right; otherwise it is on the left.
If i > the number of specifiers in fmt, the value of argument x_i
does not contribute to the printing. However, as all arguments
are evaluated before printing occurs, side-effects of the
evaluation of x_i might affect the result.
If the i-th specifier is of numerical type, any numbers in the
printing of x_i will be printed in the specified format, unless
this is modified by the printing procedure for x_i's type. Any
specified precision will be ignored except for floating-point
mode.
The (g) general format will print the as real (f) (decimal or
floating point) or as an exponential (e) depending on the
configuration parameter "display".
In the case of floating-point (f) format, and the (g) general
format, the precision determines the maximum number of decimal
places to be displayed. Other aspects of this printing may be
affected by the configuration parameters "outround", "tilde",
"fullzero", "leadzero".
IMPORTANT NOTES:
In calc, %d formats in base 10 according to the current
config("mode"). Therefore this will print the entire
"1.2345" value:
; printf("%d\n", 1.2345);
1.2345
assuming printing of 4 or more digits is allowed by the current
value of display().
See also:
; help printf
; help display
; help mode
In calc, %x formats in base 16. A non-integer numeric values such
as 1/3 is represented as a fraction. When fractions are printed
in %x format, both the numerator and denominator are printed
as is mode("fraction"):
; printf("%x\n", 1.2345);
0x9a5/0x7d0
See also:
; help printf
; help display
; help mode
Because calc is capable of of printing very large values, some
people may be surprised when this does not print the entire
value of M(23209):
fprintf(fd, "%d\n", 2^23209-1);
/* the entire value may not be printed yet */
Because I/O is usually buffered to files, the above fprintf()
may print only the initial 4096 characters. One needs to also
flush (or close the stream) to be sure that the entire
value as been printed to the file:
; fflush(fd);
A similar problem an arise when printing many digits after
the decimal point:
; display(10000),;
; fprintf(fd, "%d\n", pi(1e-10000));
; fflush(fd);
The buffer will also be flushed during a call to fclose():
; fclose(fd);
EXAMPLE
; config("epsilon", 1e-6),;
: config("display", 6),;
; config("tilde", 1),;
; config("outround", 0),;
; config("fullzero", 0),;
; fmt = "%f,%10f,%-10f,%10.4f,%.4f,%.f.\n";
; a = sqrt(3);
; printf(fmt,a,a,a,a,a,a);
1.732051, 1.732051,1.732051 , ~1.7320,~1.7320,~1.
; fd = fopen("/tmp/test.txt", "w+");
; fprintf(fd, "%d\n", 2^23209-1);
; /* one must flush to be buffered output is written */
; fflush(fd);
; display(10000),;
; fprintf(fd, "%d\n", pi(1e-10000));
; /* closing the file will also flush the buffer */
; fclose(fd);
; printf("%x\n", 1.2345);
0x9a5/0x7d0
; config("display", 5),;
: config("tilde", 0),;
; printf("%f\n", pi());
3.1416
; config("display", 10),;
; printf("%f\n", pi());
3.141592654
; config("tilde", 0),;
: config("outround",24),;
; config("fullzero", 1),;
; printf(fmt,a,a,a,a,a,a);
1.732051, 1.732051,1.732051 , 1.7321,1.7321,2.
; mat A[4] = {sqrt(2), 3/7, "undefined", null()};
; printf("%f%r",A,A);
mat [4] (4 elements, 4 nonzero):
[0] = 1.414214
[1] = .428571
[2] = "undefined"
[3] = NULL
mat [4] (4 elements, 4 nonzero):
[0] = 707107/500000
[1] = 3/7
[2] = "undefined"
[3] = NULL
; config("display", 50),;
; printf("%g %g\n%g %g\n", 1e5, 1e49, 1e50, 1e500);
100000 100000000000000000000000000000000000000000000000000
1e50 1e500
; config("display", 10),;
: config("tilde", 0),;
; printf("%f %f %f\n%f %f %f\n",
exp(1), exp(2), exp(3), exp(4), exp(5), exp(6));
2.7182818285 7.3890560989 20.0855369232
54.5981500331 148.4131591026 403.4287934927
; printf("%e %e %e\n%e %e %e\n",
exp(1), exp(2), exp(3), exp(4), exp(5), exp(6));
2.7182818285 7.3890560989 2.0085536923e1
5.4598150033e1 1.4841315910e2 4.0342879349e2
; printf("%g %g %g\n%g %g %g\n",
exp(1), exp(2), exp(3), exp(4), exp(5), exp(6));
2.718281828 7.389056099 20.08553692
54.59815003 148.4131591 403.4287935
; config("display", 10),;
; config("tilde", 0),;
; printf("%f %f %f\n%f %f %f\n",
exp(20), exp(21), exp(22), exp(23), exp(24), exp(25));
485165195.4097902780 1318815734.4832146972 3584912846.1315915617
9744803446.2489026000 26489122129.8434722941 72004899337.3858725242`
; printf("%e %e %e\n%e %e %e\n",
exp(20), exp(21), exp(22), exp(23), exp(24), exp(25));
4.8516519541e8 1.3188157345e9 3.5849128461e9
9.7448034462e9 2.6489122130e10 7.2004899337e10
; printf("%g %g %g\n%g %g %g\n",
exp(20), exp(21), exp(22), exp(23), exp(24), exp(25));
485165195.4 1318815734 3584912846
9744803446 2.648912213e10 7.200489934e10
; /*
* NOTE: When displaying many digits after the decimal point
* be sure to set display(digits) (see 'help display') to
* large enough AND to set epsilon(eps) (see 'help epsilon')
* small enough (or if the function has a esp argument,
* give a eps argument that is small enough) to display
* the value correctly.
*/
; config("tilde", 1),;
; /* NOTE: display has too few digits and epsilon is not small enough */
; display(12),;
; printf("%f\n", pi(1e-10));
3.1415926536
; epsilon(1e-10),;
; printf("%f\n", pi());
3.1415926536
; /* NOTE: display has too few digits yet epsilon is small enough */
; display(12),;
; printf("%f\n", pi(1e-72));
~3.141592653590
; epsilon(1e-72),;
; printf("%f\n", pi());
~3.141592653590
; /* NOTE: display has enough digits but epsilon is not small enough */
; display(72),;
; printf("%f\n", pi(1e-10));
3.1415926536
; epsilon(1e-10),;
; printf("%f\n", pi());
3.1415926536
/* NOTE: display has enough digits and epsilon is small enough */
; display(72),;
; printf("%f\n", pi(1e-72));
3.141592653589793238462643383279502884197169399375105820974944592307816406
; epsilon(1e-72),;
; printf("%f\n", pi());
3.141592653589793238462643383279502884197169399375105820974944592307816406
LIMITS
The number of arguments of printf() is not to exceed 1024.
LINK LIBRARY
none
SEE ALSO
config, display, epsilon, fclose, fflush, fopen, fprintf, strprintf
## Copyright (C) 1999-2006,2018,2021 Landon Curt Noll
##
## Calc is open software; you can redistribute it and/or modify it under
## the terms of the version 2.1 of the GNU Lesser General Public License
## as published by the Free Software Foundation.
##
## Calc is distributed in the hope that it will be useful, but WITHOUT
## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
## or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General
## Public License for more details.
##
## A copy of version 2.1 of the GNU Lesser General Public License is
## distributed with calc under the filename COPYING-LGPL. You should have
## received a copy with calc; if not, write to Free Software Foundation, Inc.
## 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
##
## Under source code control: 1996/03/12 22:50:41
## File existed as early as: 1996
##
## chongo <was here> /\oo/\ http://www.isthe.com/chongo/
## Share and enjoy! :-) http://www.isthe.com/chongo/tech/comp/calc/
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