PRINTF(3S) —
NAME
printf, fprintf, sprintf − formatted output conversion
SYNOPSIS
#include <stdio.h>
printf(format [, arg ] ... )
char ∗format;
fprintf(stream, format [, arg ] ... )
FILE ∗stream;
char ∗format;
sprintf(s, format [, arg ] ... )
char ∗s, format;
#include <varargs.h>
_doprnt(format, args, stream)
char ∗format;
va_list ∗args;
FILE ∗stream;
DESCRIPTION
Printf places output on the standard output stream stdout. Fprintf places output on the named output stream. Sprintf places “output” in the string s, followed by the character ‘\0’. These routines work by calling the internal routine _doprnt, using the variable-length argument facilities of varargs(3).
Each of these functions converts, formats, and prints its arguments under control of the format. The format is a character string that contains two types of objects: plain characters, which are simply copied to the output stream, and conversion specifications, each of which causes conversion and printing of the next successive argument to printf.
Each conversion specification is introduced by the character “%”. The remainder of the conversion specification includes in the following order:
• Zero or more of the following flags:
− A “#” character specifying that the value should be converted to an alternate form. For c, d, s, and u, conversions, this option has no effect. For o conversions, the precision of the number is increased to force the first character of the output string to a zero. For x(X) conversion, a non-zero result has the string 0x(0X) prepended to it. For e, E, f, g, and G, conversions, the result will always contain a decimal point, even if no digits follow the point (normally, a decimal point only appears in the results of those conversions if a digit follows the decimal point). For g and G conversions, trailing zeros are not removed from the result as they would otherwise be.
− A minus sign “−” which specifies left adjustment of the converted value in the indicated field.
− A blank which specifies that a blank is to precede any non-negative value in d, e, E, f, g, or G conversion.
− A plus sign “+” which specifies that a “+” is to precede any non-negative value in d, e, E, f, g, or G conversion. A “+” overrides a blank.
• An optional decimal digit string specifying a field width. If the converted value has fewer characters than the field width, it will be blank-padded on the left (or on the right, if the left-adjustment indicator has been given) to make up the field width. (The field width string may begin with an optional zero “0” to specify left-padding with zeroes rather than blanks. This option is ignored for infinity and NaN values.)
• An optional period “.” which serves to separate the field width from the next digit string.
• An optional decimal digit string specifying a precision that specifies the number of digits to appear after the decimal point, for e, E, and f conversion; the minimum number of digits to appear for integer conversions; or the maximum number of characters to be printed from a string.
• The character l specifying that a following d, o, x, or u corresponds to a long integer arg. Not needed; has no effect.
• An optional character h specifying that a following d, o, x, X or u corresponds to a short integer arg. Not needed; has no effect.
• A character which indicates the type of conversion to be applied.
A field width or precision may be “∗” instead of a digit string; the next arg is an integer supplying the field width or precision. Precisions must be non-negative integer values. A negative arg for field width represents both a ’−’ flag and a field width of |arg|. The maximum field width for both string and numeric conversions is 30,000; the maximum precision specification is 500 for floating-point conversions and 100 for integer conversions.
The conversion characters and their meanings are:
d,o,x,X
The integer arg is converted to decimal, octal, or hexadecimal notation, respectively; x uses “abcdef”; X uses “ABCDEF”.
f The float or double arg is converted to decimal notation in the style “[−]ddd.ddd” where the number of d’s after the decimal point is equal to the precision specification for the argument. If the precision is unspecified, 6 digits are produced; if the precision is explicitly 0, no digits and no decimal point are produced. Infinity prints as INF; NaNs print as NAN().
e,E The float or double arg is converted in the style “[−]d.ddde±dd” where there is one digit before the decimal point and the number after is equal to the precision specification for the argument. If the precision is unspecified, six digits are produced. Infinity prints as INF; NaNs print as NAN().
g,G The float or double value is converted to an f-format string, if appropriate, or an e- or E-format string, if not. The precision specification (if not specified, 6) designates the number of significant digits. Trailing zeros are stripped. Infinity prints as INF; NaNs print as NAN().
c The character arg is printed.
s Arg is taken to be a string (character pointer) and characters from the string are printed until a null character or until the number of characters indicated by the precision specification is reached; however, if the precision is 0 or unspecified, all characters up to a null or the maximum string field width are printed.
u The unsigned integer arg is converted to decimal and printed (the result will be in the range 0 through MAXUINT, where MAXUINT equals 4294967295).
% Print a “%”; no argument is converted.
D,O,U
Obsolete equivalent to ld,lo,lu.
A nonexistent or small field width does not cause truncation of a field; padding takes place only if the specified field width exceeds the actual width. Characters generated by printf are printed by putc(3S).
EXAMPLES
To print a date and time in the form “Sunday, July 3, 10:02”, where weekday and month are pointers to null-terminated strings:
printf("%s, %s %d, %02d:%02d", weekday, month, day, hour, min);
To print π to 5 decimals:
printf("pi = %.5f", 4∗atan(1.0));
To print a floating-point value to full precision while minimizing the number of digits:
printf ("%.17g", value);
SEE ALSO
PRPQs 5799-WZQ/5799-PFF: IBM/4.3 — Dec 1987