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 which causes conversion and printing of the next successive arg.
Each conversion specification is introduced by the 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 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 flag characters and their meanings are:
− The result of the conversion will be left-justified within the field.
+ The result of a signed conversion will always begin with a sign (+ or −).
blank If the first character of a signed conversion is not a sign, a blank will be prepended to the result. This implies that if the blank and + flags both appear, the blank flag will be ignored.
# The value is to be converted to an alternate 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 will have 0x or 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. A decimal point usually appears in the result of these conversions only if a digit follows it. For g and G conversions, trailing zeroes will not be removed from the result as they usually are.
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. The style used depends on the value converted style: style e will be 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 decimal point appears only if it is followed by a digit.
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 (the result will be in the range 0 through MAXUINT, where MAXUINT equals 4294967295 on a VAX-11 and 65535 on a PDP-11).
% 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(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));
ENVIRONMENT
In the ULTRIX 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 sprintfor value if an output error was encountered.
RESTRICTIONS
Very wide fields (>128 characters) fail.