ansistdio.html

Vxworks API操作系统和驱动程序设计API。压缩的HTML文件

    )
</pre>

</blockquote><h4>DESCRIPTION</h4><blockquote><p>
This routine opens a file whose name is the string pointed to by <i>file</i>
and associates a stream with it.
The argument <i>mode</i> points to a string beginning with one of the following 
sequences:
<dl>
<dt>
<b>r</b>
<dd>
open text file for reading
<dt>
<b>w</b>
<dd>
truncate to zero length or create text file for writing
<dt>
<b>a</b>
<dd>
append; open or create text file for writing at end-of-file
<dt>
<b>rb</b>
<dd>
open binary file for reading
<dt>
<b>wb</b>
<dd>
truncate to zero length or create binary file for writing
<dt>
<b>ab</b>
<dd>
append; open or create binary file for writing at end-of-file
<dt>
<b>r+</b>
<dd>
open text file for update (reading and writing)
<dt>
<b>w+</b>
<dd>
truncate to zero length or create text file for update.
<dt>
<b>a+</b>
<dd>
append; open or create text file for update, writing at end-of-file
<dt>
<b>r+b / rb+</b>
<dd>
open binary file for update (reading and writing)
<dt>
<b>w+b / wb+</b>
<dd>
truncate to zero length or create binary file for update
<dt>
<b>a+b / ab+</b>
<dd>
append; open or create binary file for update, writing at end-of-file
</dl>

<p>
Opening a file with read mode (<b>r</b> as the first character in the <i>mode</i>
argument) fails if the file does not exist or cannot be read.
<p>
Opening a file with append mode (<b>a</b> as the first character in the <i>mode</i>
argument) causes all subsequent writes to the file to be forced to the
then current end-of-file, regardless of intervening calls to <b><a href="./ansiStdio.html#fseek">fseek</a>(&nbsp;)</b>.  In
some implementations, opening a binary file with append mode (<b>b</b> as the
second or third character in the <i>mode</i> argument) may initially position
the file position indicator for the stream beyond the last data written,
because of null character padding.  In VxWorks, whether append mode is
supported is device-specific.
<p>
When a file is opened with update mode (<b>+</b> as the second or third
character in the <i>mode</i> argument), both input and output may be performed
on the associated stream.  However, output may not be directly followed by
input without an intervening call to <b><a href="./ansiStdio.html#fflush">fflush</a>(&nbsp;)</b> or to a file positioning
function (<b><a href="./ansiStdio.html#fseek">fseek</a>(&nbsp;)</b>, <b><a href="./ansiStdio.html#fsetpos">fsetpos</a>(&nbsp;)</b>, or <b><a href="./ansiStdio.html#rewind">rewind</a>(&nbsp;)</b>), and input may not be directly
followed by output without an intervening call to a file positioning
function, unless the input operation encounters end-of-file.  Opening (or
creating) a text file with update mode may instead open (or create) a
binary stream in some implementations.
<p>
When opened, a stream is fully buffered if and only if it can be determined
not to refer to an interactive device.  The error and end-of-file
indicators for the stream are cleared.
<p>
</blockquote><h4>INCLUDE FILES</h4><blockquote><p>
<b>stdio.h</b> 
<p>
</blockquote><h4>RETURNS</h4><blockquote><p>
<p>
A pointer to the object controlling the stream, or a null pointer if the
operation fails.
<p>
</blockquote><h4>SEE ALSO</h4><blockquote><p>
<b><a href="./ansiStdio.html#top">ansiStdio</a></b>, <b><a href="./ansiStdio.html#fdopen">fdopen</a>(&nbsp;)</b>, <b><a href="./ansiStdio.html#freopen">freopen</a>(&nbsp;)</b>

<hr>
<a name="fprintf"></a>
<p align=right>
<a href="rtnIndex.htm"><i>OS Libraries :  Routines</i></a></p>

</blockquote><h1>fprintf(&nbsp;)</h1> <blockquote></a></blockquote><h4>NAME</h4><blockquote>  
<p><strong>fprintf(&nbsp;)</strong> - write a formatted string to a stream (ANSI)</p>

</blockquote><h4>SYNOPSIS</h4><blockquote><p>
<pre>int fprintf
    (
    FILE *       fp,          /* stream to write to */
    const char * fmt,         /* format string */
                 ...          /* optional arguments to format string */
    )
</pre>

</blockquote><h4>DESCRIPTION</h4><blockquote><p>
This routine writes output to a specified stream under control of the string
<i>fmt</i>. The string <i>fmt</i> contains ordinary characters, which are written
unchanged, plus conversion specifications, which cause the arguments that
follow <i>fmt</i> to be converted and printed as part of the formatted string.
<p>
The number of arguments for the format is arbitrary, but they must
correspond to the conversion specifications in <i>fmt</i>.  If there are
insufficient arguments, the behavior is undefined.  If the format is
exhausted while arguments remain, the excess arguments are evaluated but
otherwise ignored.  The routine returns when the end of the format string
is encountered.
<p>
The format is a multibyte character sequence, beginning and ending in its
initial shift state.  The format is composed of zero or more directives:
ordinary multibyte characters (not <b>%</b>) that are copied unchanged to the
output stream; and conversion specification, each of which results in
fetching zero or more subsequent arguments.  Each conversion specification
is introduced by the <b>%</b> character.  After the <b>%</b>, the following appear in
sequence:
<ul>

<li>Zero or more flags (in any order) that modify the meaning of the </li>
conversion specification.
<li>An optional minimum field width.  If the converted value has fewer</li>
characters than the field width, it will be padded with spaces (by
default) on the left (or right, if the left adjustment flag, 
described later, has been given) to the field width. The field
width takes the form of an asterisk (<b>*</b>) (described later) or a decimal
integer.
<li>An optional precision that gives the minimum number of digits to</li>
appear for the <b>d</b>, <b>i</b>, <b>o</b>, <b>u</b>, <b>x</b>, and <b>X</b> conversions, the number of 
digits to appear after the decimal-point character for <b>e</b>, <b>E</b>, and <b>f</b>
conversions, the maximum number of significant digits for the <b>g</b> and
<b>G</b> conversions, or the maximum number of characters to be written 
from a string in the <b>s</b> conversion.  The precision takes the form of a 
period (<b>.</b>) followed either by an asterisk (<b>*</b>) (described later) or by
an optional decimal integer; if only the period is specified, the 
precision is taken as zero.  If a precision appears with any other
conversion specifier, the behavior is undefined.
<li>An optional <b>h</b> specifying that a following <b>d</b>, <b>i</b>, <b>o</b>, <b>u</b>, <b>x</b>, and</li>
<b>X</b> conversion specifier applies to a <b>short int</b> or <b>unsigned short int</b>
argument (the argument will have been promoted according to the integral
promotions, and its value converted to <b>short int</b> or
<b>unsigned short int</b> before printing); an optional <b>h</b> specifying that a
following <b>n</b> conversion specifier applies to a pointer to a <b>short int</b>
argument; an optional <b>l</b> (el) specifying that a following <b>d</b>, <b>i</b>, <b>o</b>,
<b>u</b>, <b>x</b>, and <b>X</b> conversion specifier applies to a <b>long int</b> or
<b>unsigned long int</b> argument; or an optional <b>l</b> specifying that a following
<b>n</b> conversion specifier applies to a pointer to a <b>long int</b>
argument.  If an <b>h</b> or <b>l</b> appears with any other conversion
specifier, the behavior is undefined.
<p>
</blockquote><h4>WARNING</h4><blockquote><p>
ANSI C also specifies an optional <b>L</b> in some of the same
contexts as <b>l</b> above, corresponding to a <b>long double</b> argument.
However, the current release of the VxWorks libraries does not support 
<b>long double</b> data; using the optional <b>L</b> gives unpredictable results.
<li>A character that specifies the type of conversion to be applied.</li>
</ul>

<p>

As noted above, a field width, or precision, or both, can be indicated by
an asterisk (<b>*</b>).  In this case, an <b>int</b> argument supplies the field width
or precision.  The arguments specifying field width, or precision, or both,
should appear (in that order) before the argument (if any) to be converted.
A negative field width argument is taken as a <b>-</b> flag followed by a positive
field width.  A negative precision argument is taken as if the precision
were omitted.
<p>
The flag characters and their meanings are:
<dl>
<dt>
<b>-</b>
<dd>
The result of the conversion will be left-justified within the field.
(it will be right-justified if this flag is not specified.)
<dt>
<b>+</b>
<dd>
The result of a signed conversion will always begin with a plus or 
minus sign.  (It will begin with a sign only when a negative value
is converted if this flag is not specified.)
<dt>
<b>space</b>
<dd>
If the first character of a signed conversion is not a sign, or 
if a signed conversion results in no characters, a space will be 
prefixed to the result.  If the <b>space</b> and <b>+</b> flags both appear, the
<b>space</b> flag will be ignored.
<dt>
<b>#</b>
<dd>
The result is to be converted to an "alternate form."  For <b>o</b> conversion
it increases the precision to force the first digit of the result to be a
zero.  For <b>x</b> (or <b>X</b>) conversion, a non-zero result will have "0x" (or
"0X") prefixed to it.  For <b>e</b>, <b>E</b>, <b>f</b>, <b>g</b>, and <b>G</b> conversions, the
result will always contain a decimal-point character, even if no digits
follow it.  (Normally, a decimal-point character appears in the result of
these conversions only if no digit follows it).  For <b>g</b> and <b>G</b>
conversions, trailing zeros will not be removed from the result.  For
other conversions, the behavior is undefined.
<dt>
<b>0</b>
<dd>
For <b>d</b>, <b>i</b>, <b>o</b>, <b>u</b>, <b>x</b>, <b>X</b>, <b>e</b>, <b>E</b>, <b>f</b>, <b>g</b>, and <b>G</b> conversions,
leading zeros (following any indication of sign or base) are used to pad
to the field width; no space padding is performed.  If the <b>0</b> and <b>-</b>
flags both appear, the <b>0</b> flag will be ignored.  For <b>d</b>, <b>i</b>, <b>o</b>, <b>u</b>,
<b>x</b>, and <b>X</b> conversions, if a precision is specified, the <b>0</b> flag will
be ignored.  For other conversions, the behavior is undefined.
</dl>

<p>
The conversion specifiers and their meanings are:
<dl>
<dt>
<b>d</b>, <b>i</b>
<dd>
The <b>int</b> argument is converted to signed decimal in the style
<b>[-]dddd</b>.  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 zeros.  The
default precision is 1.  The result of converting a zero value
with a precision of zero is no characters.
<dt>
<b>o</b>, <b>u</b>, <b>x</b>, <b>X</b>
<dd>
The <b>unsigned int</b> argument is converted to unsigned octal (<b>o</b>),
unsigned decimal (<b>u</b>), or unsigned hexadecimal notation (<b>x</b> or <b>X</b>)
in the style <b>dddd</b>; the letters abcdef are used for <b>x</b> conversion
and the letters ABCDEF for <b>X</b> 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 zeros.  The default precision is 1.  The
result of converting a zero value with a precision of zero is 
no characters.
<dt>
<b>f</b>
<dd>
The <b>double</b> argument is converted to decimal notation in the 
style <b>[-]ddd.ddd</b>, 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 precision is zero
and the <b>#</b> flag is not specified, no decimal-point character
appears.  If a decimal-point character appears, at least one 
digit appears before it.  The value is rounded to the appropriate
number of digits.
<dt>
<b>e</b>, <b>E</b>
<dd>
The <b>double</b> argument is converted in the style <b>[-]d.ddde+/-dd</b>,
where there is one digit before the decimal-point character 
(which is non-zero if the argument is non-zero) and the number
of digits after it is equal to the precision; if the precision
is missing, it is taken as 6; if the precision is zero and the 
<b>#</b> flag is not specified, no decimal-point character appears.  The
value is rounded to the appropriate number of digits.  The <b>E</b>
conversion specifier will produce a number with <b>E</b> instead of <b>e</b>
introducing the exponent.  The exponent always contains at least
two digits.  If the value is zero, the exponent is zero.
<dt>
<b>g</b>, <b>G</b>
<dd>
The <b>double</b> argument is converted in style <b>f</b> or <b>e</b> (or in style 
<b>E</b> in the case of a <b>G</b> conversion specifier), with the precision
specifying the number of significant digits.  If the precision
is zero, it is taken as 1.  The style used depends on the 
value converted; style <b>e</b> (or <b>E</b>) will be used only if the 
exponent resulting from such a conversion is less than -4 or 
greater than or equal to the precision.  Trailing zeros are
removed from the fractional portion of the result; a decimal-point
character appears only if it is followed by a digit.
<dt>
<b>c</b>
<dd>
The <b>int</b> argument is converted to an <b>unsigned char</b>, and the