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authorTobias Klauser <tklauser@distanz.ch>2008-01-27 11:37:44 +0100
committerTobias Klauser <tklauser@xenon.tklauser.home>2008-01-27 11:37:44 +0100
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+<TITLE>vfprintf</TITLE>
+<body bgcolor="#ffffcc">
+<hr>
+<pre>
+
+
+
+<h3>PRINTF(3) Linux Programmer's Manual PRINTF(3)
+</h3>
+
+<h3>NAME
+</h3> printf, fprintf, sprintf, vprintf, vfprintf, vsprintf -
+ formatted output conversion
+
+<h3>SYNOPSIS
+</h3> #include &lt;stdio.h&gt;
+
+ int printf( const char *format, ...);
+ int fprintf( FILE *stream, const char *format, ...);
+ int sprintf( char *str, const char *format, ...);
+
+ #include &lt;stdarg.h&gt;
+
+ int vprintf( const char *format, va_list ap);
+ int vfprintf( FILE *stream, const char *format, va_list
+ ap);
+ int vsprintf( char *str, char *format, va_list ap);
+
+<h3>DESCRIPTION
+</h3> The printf family of functions produces output according
+ to a format as described below. Printf and vprintf write
+ output to stdout, the standard output stream; fprintf and
+ vfprintf write output to the given output stream; sprintf,
+ and vsprintf write to the character string str. These
+ functions write the output under the control of a format
+ string that specifies how subsequent arguments (or argu-
+ ments accessed via the variable-length argument facilities
+ of stdarg(3) are converted for output. These functions
+ return the number of characters printed (not including the
+ trailing `\0' used to end output to strings).
+
+ The format string is composed of zero or more directives:
+ ordinary characters (not %), which are copied unchanged to
+ the output stream; and conversion specifications, each of
+ which results in fetching zero or more subsequent argu-
+ ments. Each conversion specification is introduced by the
+ character %. The arguments must correspond properly
+ (after type promotion) with the conversion specifier.
+ After the %, the following appear in sequence:
+
+ o Zero or more of the following flags:
+
+ # specifying that the value should be con-
+ verted to an ``alternate form''. For c, d,
+ i, n, p, s, and u conversions, this option
+ has no effect. For o conversions, the pre-
+ cision of the number is increased to force
+ the first character of the output string to
+ a zero (except if a zero value is printed
+ with an explicit precision of zero). For x
+ and X conversions, a non-zero result has the
+ string `0x' (or `0X' for X conversions)
+ prepended to it. For e, E, f, g, and G con-
+ versions, the result will always contain a
+
+
+
+<h3>BSD MANPAGE 29 November 1993 1
+</h3>
+
+
+
+
+<h3>PRINTF(3) Linux Programmer's Manual PRINTF(3)
+</h3>
+
+ decimal point, even if no digits follow it
+ (normally, a decimal point appears in the
+ results of those conversions only if a digit
+ follows). For g and G conversions, trailing
+ zeros are not removed from the result as
+ they would otherwise be.
+
+ 0 specifying zero padding. For all conver-
+ sions except n, the converted value is
+ padded on the left with zeros rather than
+ blanks. If a precision is given with a
+ numeric conversion (d, i, o, u, i, x, and
+ X), the 0 flag is ignored.
+
+ - (a negative field width flag) indicates the
+ converted value is to be left adjusted on
+ the field boundary. Except for n conver-
+ sions, the converted value is padded on the
+ right with blanks, rather than on the left
+ with blanks or zeros. A - overrides a 0 if
+ both are given.
+
+ (a space) specifying that a blank should be
+ left before a positive number produced by a
+ signed conversion (d, e, E, f, g, G, or i).
+
+ + specifying that a sign always be placed
+ before a number produced by a signed conver-
+ sion. A + overrides a space if both are
+ used.
+
+ o An optional decimal digit string specifying a mini-
+ mum field width. If the converted value has fewer
+ characters than the field width, it will be padded
+ with spaces on the left (or right, if the left-
+ adjustment flag has been given) to fill out the
+ field width.
+
+ o An optional precision, in the form of a period
+ (`.') followed by an optional digit string. If
+ the digit string is omitted, the precision is taken
+ as zero. This gives the minimum number of digits
+ to appear for d, i, o, u, x, and X conversions, the
+ number of digits to appear after the decimal-point
+ for e, E, and f conversions, the maximum number of
+ significant digits for g and G conversions, or the
+ maximum number of characters to be printed from a
+ string for s conversions.
+
+ o The optional character h, specifying that a follow-
+ ing d, i, o, u, x, or X conversion corresponds to a
+ short int or unsigned short int argument, or that a
+ following n conversion corresponds to a pointer to
+ a short int argument.
+
+
+
+<h3>BSD MANPAGE 29 November 1993 2
+</h3>
+
+
+
+
+<h3>PRINTF(3) Linux Programmer's Manual PRINTF(3)
+</h3>
+
+ o The optional character l (ell) specifying that a
+ following d, i, o, u, x, or X conversion applies to
+ a pointer to a long int or unsigned long int argu-
+ ment, or that a following n conversion corresponds
+ to a pointer to a long int argument.
+
+ o The character L specifying that a following e, E,
+ f, g, or G conversion corresponds to a long double
+ argument.
+
+ o A character that specifies the type of conversion
+ to be applied.
+
+ A field width or precision, or both, may be indicated by
+ an asterisk `*' instead of a digit string. In this case,
+ an int argument supplies the field width or precision. A
+ negative field width is treated as a left adjustment flag
+ followed by a positive field width; a negative precision
+ is treated as though it were missing.
+
+ The conversion specifiers and their meanings are:
+
+ diouxX The int (or appropriate variant) argument is con-
+ verted to signed decimal (d and i), unsigned octal
+ (o, unsigned decimal (u, or unsigned hexadecimal (x
+ and X) notation. The letters abcdef are used for x
+ conversions; the letters ABCDEF are used for X con-
+ versions. The precision, if any, gives the minimum
+ number of digits that must appear; if the converted
+ value requires fewer digits, it is padded on the
+ left with zeros.
+
+ DOU The long int argument is converted to signed deci-
+ mal, unsigned octal, or unsigned decimal, as if the
+ format had been ld, lo, or lu respectively. These
+ conversion characters are deprecated, and will
+ eventually disappear.
+
+ eE The double argument is rounded and converted in the
+ style [-]d.dddedd where there is one digit before
+ the decimal-point character and the number of dig-
+ its after it is equal to the precision; if the pre-
+ cision is missing, it is taken as 6; if the preci-
+ sion is zero, no decimal-point character appears.
+ An E conversion uses the letter E (rather than e)
+ to introduce the exponent. The exponent always
+ contains at least two digits; if the value is zero,
+ the exponent is 00.
+
+ f The double argument is rounded and converted to
+ decimal notation in the style [-]ddd.ddd, where the
+ number of digits after the decimal-point character
+ is equal to the precision specification. If the
+ precision is missing, it is taken as 6; if the
+
+
+
+<h3>BSD MANPAGE 29 November 1993 3
+</h3>
+
+
+
+
+<h3>PRINTF(3) Linux Programmer's Manual PRINTF(3)
+</h3>
+
+ precision is explicitly zero, no decimal-point
+ character appears. If a decimal point appears, at
+ least one digit appears before it.
+
+ g The double argument is converted in style f or e
+ (or E for G conversions). The precision specifies
+ the number of significant digits. If the precision
+ is missing, 6 digits are given; if the precision is
+ zero, it is treated as 1. Style e is used if the
+ exponent from its conversion is less than -4 or
+ greater than or equal to the precision. Trailing
+ zeros are removed from the fractional part of the
+ result; a decimal point appears only if it is fol-
+ lowed by at least one digit.
+
+ c The int argument is converted to an unsigned char,
+ and the resulting character is written.
+
+ s The ``char *'' argument is expected to be a pointer
+ to an array of character type (pointer to a
+ string). Characters from the array are written up
+ to (but not including) a terminating NUL character;
+ if a precision is specified, no more than the num-
+ ber specified are written. If a precision is
+ given, no null character need be present; if the
+ precision is not specified, or is greater than the
+ size of the array, the array must contain a termi-
+ nating NUL character.
+
+ p The ``void *'' pointer argument is printed in hex-
+ adecimal (as if by %#x or %#lx).
+
+ n The number of characters written so far is stored
+ into the integer indicated by the ``int *'' (or
+ variant) pointer argument. No argument is con-
+ verted.
+
+ % A `%' is written. No argument is converted. The
+ complete conversion specification is `%%'.
+
+ In no case does a non-existent or small field width cause
+ truncation of a field; if the result of a conversion is
+ wider than the field width, the field is expanded to con-
+ tain the conversion result.
+
+
+<h3>EXAMPLES
+</h3> To print a date and time in the form `Sunday, July 3,
+ 10:02', where weekday and month are pointers to strings:
+ #include &lt;stdio.h&gt;
+ fprintf(stdout, "%s, %s %d, %.2d:%.2d\n",
+ weekday, month, day, hour, min);
+
+ To print to five decimal places:
+
+
+
+<h3>BSD MANPAGE 29 November 1993 4
+</h3>
+
+
+
+
+<h3>PRINTF(3) Linux Programmer's Manual PRINTF(3)
+</h3>
+
+ #include &lt;math.h&gt;
+ #include &lt;stdio.h&gt;
+ fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0));
+
+ To allocate a 128 byte string and print into it:
+ #include &lt;stdio.h&gt;
+ #include &lt;stdlib.h&gt;
+ #include &lt;stdarg.h&gt;
+ char *newfmt(const char *fmt, ...)
+ {
+ char *p;
+ va_list ap;
+ if ((p = malloc(128)) == NULL)
+ return (NULL);
+ va_start(ap, fmt);
+ (void) vsnprintf(p, 128, fmt, ap);
+ va_end(ap);
+ return (p);
+ }
+
+</pre>
+<hr>
+<h3>SEE ALSO
+</h3><p>
+<a href=printf.htm>printf</a>,
+<a href=scanf.htm>scanf</a>,
+<pre>
+
+<h3>STANDARDS
+</h3> The fprintf, printf, sprintf, vprintf, vfprintf, and
+ vsprintf functions conform to ANSI C3.159-1989 (``ANSI
+ C'').
+
+<h3>BUGS
+</h3> Some floating point conversions under Linux cause memory
+ leaks.
+
+ The conversion formats %D, %O, and %U are not standard and
+ are provided only for backward compatibility. These may
+ not be provided under Linux.
+
+ The effect of padding the %p format with zeros (either by
+ the 0 flag or by specifying a precision), and the benign
+ effect (i.e., none) of the # flag on %n and %p conver-
+ sions, as well as other nonsensical combinations such as
+ %Ld, are not standard; such combinations should be
+ avoided.
+
+ Because sprintf and vsprintf assume an infinitely long
+ string, callers must be careful not to overflow the actual
+ space; this is often impossible to assure.
+
+
+
+
+
+
+
+
+
+
+
+<h3>BSD MANPAGE 29 November 1993 5
+</h3>
+
+ </pre>
+<P>
+<hr>
+<p>
+<center>
+<table border=2 width=80%>
+<tr align=center>
+<td width=25%>
+<a href=../cref.html>Top</a>
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+<a href=../FUNCTIONS/funcref.htm>Functions</a>
+</td>
+</tr>
+</table>
+</center>
+<p>
+<hr>
+
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