PRINTF(3S)
NAME
printf, fprintf, sprintf − formatted output conversion
USAGE
#include <stdio.h>
printf(format [ , arg ] ... )
char *format;
fprintf(stream, format [ , arg ] ... )
FILE *stream;
char *format;
sprintf(s, format [, arg ] ... )
char *s, format;
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 null character “\0”.
Each of these functions converts, formats, and prints all other arguments under control of the first argument. The first argument is a character string which contains two types of objects, each of which converts and prints the next successive arg printf: plain characters, which are simply copied to the output stream, and conversion specifications.
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 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, the value will be padded with zero instead of blanks;
• 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 pound sign (#) 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 that 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 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, six digits are given; if the precision is explicitly zero, no digits and no decimal point are printed.
e The float or double arg is converted in the style “[fI−]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, six 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 zero 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 zero through MAXUINT, where MAXUINT equals 4294967295 on a VAX-11).
% Print a percent sign (%); 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));