printf(3s)

NAME

printf, fprintf, sprintf − formatted output conversion

SYNTAX

#include <stdio.h>

int printf(format [, arg ] ... )
char *format;

int fprintf(stream, format [, arg ] ... )
FILE *stream;
char *format;

Non-System V Environment

char *sprintf(s, format [, arg ] ... )
char *s, format;

System V Environment

int sprintf(s, format [, arg ] ... )
char *s, format;

DESCRIPTION

The printf subroutine places output on the standard output stream stdout. The fprintf subroutine places output on the named output stream. The sprintf subroutine places output in the string s, followed by the character ‘\0’.

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 these cause conversion and printing of the next successive arg.

Each conversion specification is introduced by the percent sign character (%). Following the %, there may be:

•Zero or more flags, which modify the meaning of the conversion specification.

•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, it is 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 occurs 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 radix character, 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 an asterisk (*) instead of a digit string. In this case an integer arg supplies the field width or precision.

The flag characters and their meanings are:

− The result of the conversion is left-justified within the field.

+ The result of a signed conversion always begins with a sign (+ or −).

blank If the first character of a signed conversion is not a sign, a blank is prepended to the result. This implies that if the blank and plus sign (+) flags both appear, the blank flag is ignored.

# The value is to be converted to an alternative form. For c, d, s, and u conversions, the flag has no effect. For o conversions, it increases the precision to force the first digit of the result to be a zero. For x or X conversions, a non-zero result has 0x or 0X prepended to it. For e, E, f, g, and G conversions, the result always contains a decimal point, even if no digits follow the point. A decimal point usually appears in the result of these conversions only if a digit follows it. For g and G conversions, trailing zeroes are not removed from the result.

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 radix character 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 radix characters are printed.

e The float or double arg is converted in the style ‘[−]d.ddde±dd’ where there is one digit before the radix character 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. The style used depends on the value converted style: style e is used only if the exponent resulting from the conversion is less than −4 or greater than the precision. Trailing zeroes are removed from the result. A radix character appears only if it is followed by a digit.

c The character arg is printed.

s The 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 is in the range 0 through MAXUINT, where MAXUINT equals 4294967295 on a VAX-11 or MIPS machine and 65535 on a PDP-11 machine).

% Print a ‘%’; no argument is converted.

A non-existent or small field width never causes 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.

In all cases, the radix character output is defined by the last successful call to setlocale category LC_NUMERIC. If setlocale category LC_NUMERIC has not been called successfully, or if the radix character is not defined, the radix character defaults to a period (.).

ENVIRONMENT

In the ULTRIX-32 environment, printf and fprintf return 0 for success and EOF for failure. The sprintf subroutine returns its first argument for success and EOF for failure.

In the System V environment, printf, fprintf, and sprintf subroutine returns the number of characters transmitted, not including the \0 in the case of sprintf or a negative value if an output error was encountered.

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));

RESTRICTIONS

Fields that exceed 128 characters fail.

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