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Minix/1.7.5/MANUALS/CAT3/PRINTF.3
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Minix/1.7.5/MANUALS/CAT3/PRINTF.3
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NAME
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printf, fprintf, sprintf - print formatted output
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SYNTAX
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#include <stdio.h>
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int printf (format [ , arg ] ... )
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char *format;
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int fprintf (stream, format [ , arg ] ... )
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FILE *stream;
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char *format;
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int sprintf (s, format [ , arg ] ... )
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char *s, format;
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DESCRIPTION
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Printf places output on the standard output stream stdout.
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Fprintf places output on the named output stream. Sprintf
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places ``output,'' followed by the null character (\0), in
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consecutive bytes starting at *s; it is the user's
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responsibility to ensure that enough storage is available.
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Each function returns the number of characters transmitted
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(not including the \0 in the case of sprintf), or a negative
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value if an output error was encountered.
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Each of these functions converts, formats, and prints its
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args under control of the format. The format is a character
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string that contains two types of objects: plain
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characters, which are simply copied to the output stream,
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and conversion specifications, each of which results in
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fetching of zero or more args. The results are undefined if
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there are insufficient args for the format. If the format
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is exhausted while args remain, the excess args are simply
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ignored.
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Each conversion specification is introduced by the character
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%. After the %, the following appear in sequence:
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Zero or more flags, which modify the meaning of the
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conversion specification.
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An optional decimal digit string specifying a minimum
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field width. If the converted value has fewer
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characters than the field width, it will be padded on
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the left (or right, if the left-adjustment flag `-',
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described below, has been given) to the field width.
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If the field width for an s conversion is preceded by a
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0, the string is right adjusted with zero-padding on
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the left.
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A precision that gives the minimum number of digits to
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appear for the d, o, u, x, or X conversions, the number
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of digits to appear after the decimal point for the e
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and f conversions, the maximum number of significant
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digits for the g conversion, or the maximum number of
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characters to be printed from a string in s conversion.
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The precision takes the form of a period (.) followed
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by a decimal digit string; a null digit string is
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treated as zero.
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An optional l (ell) specifying that a following d, o,
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u, x, or X conversion character applies to a long
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integer arg. A l before any other conversion character
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is ignored.
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A character that indicates the type of conversion to be
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applied.
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A field width or precision may be indicated by an asterisk
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(*) instead of a digit string. In this case, an integer arg
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supplies the field width or precision. The arg that is
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actually converted is not fetched until the conversion
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letter is seen, so the args specifying field width or
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precision must appear before the arg (if any) to be
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converted.
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The flag characters and their meanings are:
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- The result of the conversion will be left-
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justified within the field.
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+ The result of a signed conversion will always
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begin with a sign (+ or -).
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blank If the first character of a signed conversion is
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not a sign, a blank will be prefixed to the
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result. This implies that if the blank and +
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flags both appear, the blank flag will be ignored.
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# This flag specifies that the value is to be
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converted to an ``alternate form.'' For c, d, s,
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and u conversions, the flag has no effect. For o
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conversion, it increases the precision to force
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the first digit of the result to be a zero. For x
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or X conversion, a non-zero result will have 0x or
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0X prefixed to it. For e, E, f, g, and G
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conversions, the result will always contain a
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decimal point, even if no digits follow the point
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(normally, a decimal point appears in the result
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of these conversions only if a digit follows it).
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For g and G conversions, trailing zeroes will not
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be removed from the result (which they normally
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are).
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The conversion characters and their meanings are:
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d,o,u,x,x The integer arg is converted to signed decimal,
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unsigned octal, decimal, or hexadecimal notation
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(x and X), respectively; the letters abcdef are
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used for x conversion and the letters ABCDEF for X
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conversion. The precision specifies the minimum
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number of digits to appear; if the value being
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converted can be represented in fewer digits, it
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will be expanded with leading zeroes. (For
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compatibility with older versions, padding with
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leading zeroes may alternatively be specified by
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prepending a zero to the field width. This does
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not imply an octal value for the field width.)
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The default precision is 1. The result of
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converting a zero value with a precision of zero
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is a null string.
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f The float or double arg is converted to decimal
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notation in the style ``[-]ddd.ddd,'' where the
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number of digits after the decimal point is equal
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to the precision specification. If the precision
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is missing, six digits are output; if the
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precision is explicitly 0, no decimal point
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appears.
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e,E The float or double arg is converted in the style
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``[-]d.ddde_dd,'' where there is one digit before
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the decimal point and the number of digits after
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it is equal to the precision; when the precision
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is missing, six digits are produced; if the
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precision is zero, no decimal point appears. The
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E format code will produce a number with E instead
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of e introducing the exponent. The exponent
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always contains at least two digits.
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g,G The float or double arg is printed in style f or e
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(or in style E in the case of a G format code),
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with the precision specifying the number of
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significant digits. The style used depends on the
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value converted: style e will be used only if the
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exponent resulting from the conversion is less
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than -4 or greater than the precision. Trailing
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zeroes are removed from the result; a decimal
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point appears only if it is followed by a digit.
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c The character arg is printed.
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s The arg is taken to be a string (character
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pointer) and characters from the string are
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printed until a null character (\0) is encountered
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or the number of characters indicated by the
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precision specification is reached. If the
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precision is missing, it is taken to be infinite,
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so all characters up to the first null character
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are printed. A NULL value for arg will yield
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undefined results.
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% Print a %; no argument is converted.
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In no case does a non-existent or small field width cause
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truncation of a field; if the result of a conversion is
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wider than the field width, the field is simply expanded to
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contain the conversion result. Characters generated by
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printf and fprintf are printed as if putc(3S) had been
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called.
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EXAMPLES
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To print a date and time in the form ``Sunday, July 3,
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10:02,'' where weekday and month are pointers to null-
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terminated strings:
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printf("%s, %s %d, %d:%.2d", weekday, month, day, hour, min);
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To print pi to 5 decimal places:
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printf("pi = %.5f", 4 * atan(1.0));
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SEE ALSO
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ecvt(3C), putc(3S), scanf(3S), stdio(3S).
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