Table of Contents
The family of functions produces output according
to a as described below. and write output to the standard output stream;
and write output to the given output and write to the character
string These functions write the output under the control of a
string that specifies how subsequent arguments (or arguments accessed
via the variable-length argument facilities of are converted for output.
These functions return the number of characters printed (not including
the trailing used to end output to strings). and will
write at most of the characters printed into the output string (the character
then gets the terminating if the return value is greater than or equal
to the argument, the string was too short and some of the printed characters
were discarded. and effectively assume an infinite The format string
is composed of zero or more directives: ordinary characters (not 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 The arguments
must correspond properly (after type promotion) with the conversion specifier.
After the the following appear in sequence: Zero or more of the following
flags: A character specifying that the value should be converted to
an ‘‘alternate form’’. For and conversions, this option has no effect.
For conversions, the precision of the number is increased to force the
first character of the output string to a zero (except if a zero value
is printed with an explicit precision of zero). For and conversions, a
non-zero result has the string (or for conversions) prepended to it. For
and conversions, the result will always contain a decimal point, even
if no digits follow it (normally, a decimal point appears in the results
of those conversions only if a digit follows). For and conversions, trailing
zeros are not removed from the result as they would otherwise be. A zero
character specifying zero padding. For all conversions except the converted
value is padded on the left with zeros rather than blanks. If a precision
is given with a numeric conversion and the flag is ignored. A negative
field width flag indicates the converted value is to be left adjusted
on the field boundary. Except for conversions, the converted value is padded
on the right with blanks, rather than on the left with blanks or zeros.
A overrides a if both are given. A space, specifying that a blank should
be left before a positive number produced by a signed conversion
or A character specifying that a sign always be placed before a number
produced by a signed conversion. A overrides a space if both are used.
An optional decimal digit string 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 (or right, if the left-adjustment flag has been
given) to fill out the field width. An optional precision, in the form
of a period followed by an optional digit string. If the digit string
is omitted, the precision is taken as zero. This gives the minimum number
of digits to appear for and conversions, the number of digits to
appear after the decimal-point for and conversions, the maximum number
of significant digits for and conversions, or the maximum number of characters
to be printed from a string for conversions. The optional character specifying
that a following or conversion corresponds to a or argument, or
that a following conversion corresponds to a pointer to a argument. The
optional character (ell) specifying that a following or conversion
applies to a pointer to a or argument, or that a following conversion
corresponds to a pointer to a argument. The optional character specifying
that a following or conversion corresponds to a or argument, or
that a following conversion corresponds to a pointer to a argument. The
character specifying that a following or conversion corresponds to
a argument (but note that long double values are not currently supported
by the and compilers). A character that specifies the type of conversion
to be applied. A field width or precision, or both, may be indicated by
an asterisk instead of a digit string. In this case, an argument supplies
the field width or precision. A negative field width is treated as a left
adjustment flag followed by a positive field width; a negative precision
is treated as though it were missing. The conversion specifiers and their
meanings are: The (or appropriate variant) argument is converted to
signed decimal and unsigned octal unsigned decimal or unsigned hexadecimal
and notation. The letters are used for conversions; the letters are
used for conversions. The precision, if any, gives the minimum number of
digits that must appear; if the converted value requires fewer digits,
it is padded on the left with zeros. The argument is converted to signed
decimal, unsigned octal, or unsigned decimal, as if the format had been
or respectively. These conversion characters are deprecated, and will
eventually disappear. The argument is rounded and converted in the style
where there is one digit before the decimal-point character 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.
An conversion uses the letter (rather than to introduce the exponent.
The exponent always contains at least two digits; if the value is zero,
the exponent is 00. The argument is rounded and converted to decimal notation
in the style 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 appears, at least one digit appears before it.
The argument is converted in style or (or for conversions). The precision
specifies the number of significant digits. If the precision is missing,
6 digits are given; if the precision is zero, it is treated as 1. Style
is used if the exponent from its conversion is less than -4 or greater
than or equal to the precision. Trailing zeros are removed from the fractional
part of the result; a decimal point appears only if it is followed by at
least one digit. The argument is converted to an and the resulting character
is written. The argument is expected to be a pointer to an array of character
type (pointer to a string). Characters from the array are written up to
(but not including) a terminating character; if a precision is specified,
no more than the number specified are written. If a precision is given,
no null character need be present; if the precision is not specified, or
is greater than the size of the array, the array must contain a terminating
character. The pointer argument is printed in hexadecimal (as if by
or The number of characters written so far is stored into the integer
indicated by the (or variant) pointer argument. No argument is converted.
A is written. No argument is converted. The complete conversion specification
is In no case does a non-existent 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.
To print a date and time in the form ‘Sunday, July 3, 10:02’, where and
are pointers to strings: #include <stdio.h> fprintf(stdout, "%s, %s %d,
%.2d:%.2d\n", weekday, month, day, hour, min);
To print Pi to five decimal places: #include <math.h> #include <stdio.h>
fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0)); To allocate a 128 byte string
and print into it: #include <stdio.h> #include <stdlib.h> #include <stdarg.h> char
*newfmt(const char *fmt, ...) { char *p;
va_list ap;
if ((p = malloc(128)) == NULL)
return (NULL);
va_start(ap, fmt);
(void) vsnprintf(p, 128, fmt, ap);
va_end(ap);
return (p)
;
}
The and functions conform to
The functions
and are new to this release.
The conversion formats and are not
standard and are provided only for backward compatibility. The effect of
padding the format with zeros (either by the flag or by specifying a
precision), and the benign effect (i.e., none) of the flag on and conversions,
as well as other nonsensical combinations such as are not standard; such
combinations should be avoided. Because and assume an infinitely long
string, callers must be careful not to overflow the actual space; this
is often impossible to assure. For safety, programmers should use the interface
instead. Unfortunately, this interface is not portable.
Table of Contents