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;

char *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'. All of 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 as specified by format. 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 arg.

Each conversion specification is introduced by the character %. Following the %, there may be

•   an optional minus sign `-' which specifies left adjustment of the converted value in the indicated field;

•   an optional digit string specifying a field width; if the converted value has fewer characters than the field width, the value will be blank-padded on the left (or right, if the left-adjustment indicator has been given) to make up the field width; if the field width begins with a zero, zero-padding will be done instead of blank-padding;

•   an optional period `.' which serves to separate the field width from the next digit string;

•   an optional digit string specifying a precision which specifies the number of digits to appear after the decimal point, for e- and f-conversion, or the maximum number of characters to be printed from a string;

•   an optional `#' 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).

•   the character l specifying that a following d, o, x, or u corresponds to a long integer arg.

•   a character which indicates the type of conversion to be applied.

A field width or precision may be `*' instead of a digit string. In this case an integer arg supplies the field width or precision.

The conversion characters and their meanings are

dox The integer arg is converted to decimal, octal, or hexadecimal notation respectively.

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 missing, 6 digits are given; if the precision is explicitly 0, no digits and no decimal point are printed.

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; when the precision is missing, 6 digits are produced.

g   The float or double arg is printed in style d, in style f, or in style e, whichever gives full precision in minimum space.

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 the number of characters indicated by the precision specification is reached; however if the precision is 0 or missing, all characters up to a null 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 on the BALANCE Series or VAX-11 and 65535 on a PDP-11).

%   Print a `%'; no argument is converted.

In printing floating point types (float and double), if the exponent is 0x7FF and the mantissa is not equal to zero, then the output is

    [-]nan0xdddddddd

where 0xdddddddd is the hexadecimal representation of the leftmost 32 bits of the mantissa. If the mantissa is zero, the output is

    [±]inf

If the exponent is zero and the mantissa is not equal to zero, then the output is

    [-]den0xdddddddd

where 0xdddddddd is the hexadecimal representation of the leftmost 32 bits of the mantissa.

In no case does a non-existent or small field width 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 pi to 5 decimals:

    printf("pi = %.5f", 4*atan(1.0));

RETURN VALUES
All calls return EOF on error, zero if successful. Sprintf returns the string in the argument s.

SEE ALSO
putc(3S), scanf(3S), ecvt(3)

BUGS
Very wide fields (>128 characters) fail.