PRINTF(3)

NAME
printf, fprintf, sprintf, snprintf, vprintf, vfprintf, vsprintf, vsnprintf - formatted output conversion

SYNOPSIS
#include <sys/types.h>
#include <stdio.h>
#include <stdarg.h>
int printf(const char *format [, arg] ...);
int fprintf(FILE *stream, const char *format [, arg] ...);
int sprintf(char *s, const char *format [, arg] ...);
int snprintf(char *s, size_t n, const char *format [, arg] ...);
int vprintf(const char *format, va_list args);
int vfprintf(FILE *stream, const char *format, va_list args);
int vsprintf(char *s, const char *format, va_list args);
int vsnprintf(char *s, size_t n, const char *format, va_list args);

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'. Snprintf (Minix-vmd only) is like sprintf except that no more than n-1 characters are written to s followed by a `\0'.

The v*printf functions can be used to make functions like the first four by using the stdarg(3) method to process the argument.

Each of these functions converts, formats, and prints its arguments after the first under control of the first argument. The first argument is a character string which 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 %. The remainder of the conversion specification includes in the following order

•   Zero or more of 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 `+' character specifying that there should always be a sign placed before the number when using signed conversions.

    •   a space specifying that a blank should be left before a positive number during a signed conversion. A `+' overrides a space if both are used.

•   an optional 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 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;

•   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.

X   Like x, but use upper case instead of lower case.

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 until 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.

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

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(3).

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));

SEE ALSO
putc(3), scanf(3), ecvt(3), stdarg(3).