printf, fprintf, sprintf - output formatters


#include <stdio_p.h>

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

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

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


printf places output on the standard output stream stdout. fprintf places output on the named output stream. sprintf places "output", followed by the null character (\0) in consecutive bytes starting at * s; it is the user's responsibility to ensure that enough storage is available. Each function returns the number of characters transmitted (not including the \0 for sprintf ), or a negative value if an output error was encountered.

Each of these functins converts, formats, and prints its arg s under control of the format. The 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 results in fetching zero or more arg s. The results are undefined if there are insufficient arg s for the format. If the format is exhausted while arg s remain, the excess arg s are simply ignored.

Each conversion specification is introduced by the character %. After the %, the following appear in sequence:

A field width or precision may be indicated by an asterisk (*) instead of a digit string. Here an integer arg supplies the field width or precision. The arg that is actually converted is not fetched until the conversion letter is seen, so the arg s specifying field width or precision must appear before the arg (if any) to be converted.

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 -).

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.

This flag specifies that the value is to be converted to an "alternate form." For c, d, s, and u conversions, the flag has no effect. For o conversion, it increases the precision to force the first digit of the result to be zero. For x(X) conversion, a non-zero result will have 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 appears in the result of these conversions only if a digit follows it). For g and G conversinos, trailing zeroes will not be removed from the result (which they normally are).

The conversion characters and their meanings are:

The integer arg is converted to signed decimal, unsigned octal, decimal, or hexadecimal notation ( x and X ), respectively; the letters abcdef are used for x conversion and the letters ABCDEF for X conversion. The precision specifies the minimum number of digits to appear; if the value being converted can be represented in fewer digits, it will be expanded with leading zeroes. The default precision is 1. The result of converting a zero value with a precision of zero is a null string (unless the conversion is o, x , or X and the # flag is present).

The float or double arg is converted to decimal notation in the style "[-]ddd.ddd", where the number of digits after the decimal point is equal to the precision specification. If the precision is missing, 6 digits are output; if the precision is explicitly 0, no decimal point appears.

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 of digits after it is equal to the precision; when the precision is missing, 6 digits are produced; if the precision is zero, no decimal point appears. The E format code will produce a number with E instead of e introducing the exponent. The exponent always contains exactly two digits.

The float or double arg is printed in style f or e (or in style E for a G format code), with the precision specifying the number of significant digits. The style used depends on the value converted: 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.

The character arg is printed.

The arg is taken to be a string (character pointer) and characters from the string are printed until a null character (\0) is encountered or the number of characters indicated by the precision specification is reached. If the precision is missing, it is taken to be infinite, so all characters up to the first null character are printed.
Print a % ; no argument is converted.

Never does a non-existent or small field width cause truncation of a field; if the result of the conversion is wider than the field width, the field is simply expanded to contain the conversion result. Characters generated by printf and fprintf are printed as if putcchar had been called (see putc(3P) ).


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,  %.2d:%.2d", weekday, month, day, hour, min);
To print Pi to 5 decimal places:
printf("pi = %.5f", 4*atan(1.0));


ecvt(3P) , putc(3P) , scanf(3P) , stdio(3P).