snprintf.html

unix 下的C开发手册,还用详细的例程。

<dt>o<dd>The <b>unsigned int</b> argument is converted to unsigned octal format
in the style <i>dddd</i>.
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 0 with an explicit precision of 0 is no characters.

<dt>u<dd>The <b>unsigned int</b> argument is converted to unsigned decimal format
in the style
<i>dddd</i>.
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 0 with an explicit precision of 0 is no characters.


<dt>x<dd>The <b>unsigned int</b> argument is converted to unsigned hexadecimal format
in the style
<i>dddd</i>;
the letters abcdef are used.
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 0 with an explicit precision of 0 is no characters.


<dt>X<dd>Behaves the same as the x conversion character except that
letters ABCDEF are used instead of abcdef.

<dt>f<dd>The
<b>double</b>
argument is converted to decimal notation in the style
<b>[</b>-<b>]</b><i>ddd.ddd</i>, where the number of digits after the
radix character is equal to the precision specification.
If the precision is missing, it is taken as 6; if the precision is
explicitly 0 and no # flag is present, no radix character appears.
If a radix character appears, at least one digit appears
before it.
The value is rounded to the appropriate number of digits.

The
<i>fprintf()</i>
family of functions may make available character string representations
for infinity and NaN.

<dt>e, E<dd>The
<b>double</b>
argument is converted in the style
<b>[</b>-<b>]</b><i>d.ddd</i>e<i>&plusmn;dd</i>,
where there is one digit before the radix 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 0 and no # flag
is present, no radix character appears.
The value is rounded to the appropriate number of digits.
The E conversion character will produce a number with E instead of e
introducing the exponent.
The exponent always contains at least two digits.
If the value is 0, the exponent is 0.

The
<i>fprintf()</i>
family of functions may make available character string representations
for infinity and NaN.


<dt>g, G<dd>The
<b>double</b>
argument is converted in the style f or e (or in the style E
in the case of a G conversion character),
with the precision specifying the number of significant digits.
If an explicit precision is 0, it is taken as 1.
The style used depends on the value converted; style e (or E)
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 radix character appears only if it is followed
by a digit.

The
<i>fprintf()</i>
family of functions may make available character string representations
for infinity and NaN.


<dt>c<dd>The
<b>int</b>
argument is converted to an
<b>unsigned char</b>,
and the resulting byte is written.

If an l (ell) qualifier is present, the
<b>wint_t</b>
argument is converted as if by an ls conversion specification with no
precision and an argument that points to a two-element array of type
<b>wchar_t</b>,
the first element of which contains the 
<b>wint_t</b>
argument to the ls conversion specification and the second
element contains a null wide-character.


<dt>s<dd>The argument must be a pointer to an array of
<b>char</b>,
Bytes from the array are written up to (but not including) any
terminating null byte.
If the precision is specified, no
more than that many bytes are written.
If the precision is not specified or is greater than the size of
the array, the array must contain a null byte.

If an l (ell) qualifier is present, the argument must be a pointer to 
an array of type
<b>wchar_t</b>.
Wide-characters from the array are converted to characters
(each as if by a call to the
<i><a href="wcrtomb.html">wcrtomb()</a></i>
function, with the conversion state described by an
<b>mbstate_t</b>
object initialised to zero before the first wide-character is
converted) up to and including a terminating null wide-character.  The
resulting characters are written up to (but not including)
the terminating null character (byte).  If no precision is specified,
the array must contain a null wide-character.   If a precision is
specified, no more than that many characters (bytes) are written
(including shift sequences, if any), and the array must contain a null
wide-character if, to equal the character sequence length
given by the precision, the function would need to access a 
wide-character one past the end of the array.  In no case is a partial
character written.

<dt>p<dd>The argument must be a pointer to
<b>void</b>.
The value of the pointer is converted to a sequence of printable
characters, in an implementation-dependent manner.

<dt>n<dd>The argument must be a pointer to an integer into which is written
the number of bytes written to the output so far by this call to one of the
<i>fprintf()</i>
functions.
No argument is converted.


<dt>C<dd>Same as lc.

<dt>S<dd>Same as ls.

<dt>%<dd>Print a %; no argument is converted.
The entire conversion specification must be %%.

</dl>
<p>
If a conversion specification does not match one of the
above forms, the behaviour is undefined.
<p>
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 simply expanded to contain the conversion result.
Characters generated by
<i>fprintf()</i>
and
<i><a href="printf.html">printf()</a></i>
are printed as if
<i><a href="fputc.html">fputc()</a></i>
had been called.
<p>
The
<i>st_ctime</i>
and
<i>st_mtime</i>
fields of the file will be marked for update between the call to
a successful execution of
<i>fprintf()</i>
or
<i><a href="printf.html">printf()</a></i>
and the next successful completion of a call to
<i><a href="fflush.html">fflush()</a></i>
or
<i><a href="fclose.html">fclose()</a></i>
on the same stream or a call to
<i><a href="exit.html">exit()</a></i>
or
<i><a href="abort.html">abort()</a></i>.
</blockquote><h4><a name = "tag_000_008_807">&nbsp;</a>RETURN VALUE</h4><blockquote>
Upon successful completion, these functions
return the number of bytes transmitted
excluding the terminating null in the case of
<i>sprintf()</i>
or
<i>snprintf()</i>
or a negative value if an output error was encountered.
<p>
If the value of
<i>n</i>
is zero on a call to
<i>snprintf()</i>,
an unspecified value less than 1 is returned.
</blockquote><h4><a name = "tag_000_008_808">&nbsp;</a>ERRORS</h4><blockquote>
For the conditions under which
<i>fprintf()</i>
and
<i><a href="printf.html">printf()</a></i>
will fail and may fail, refer to
<i><a href="fputc.html">fputc()</a></i>
or
<i><a href="fputwc.html">fputwc()</a></i>.
<p>
In addition, all forms of
<i>fprintf()</i>
may fail if:
<dl compact>

<dt>[EILSEQ]<dd>
A wide-character code that does not correspond to a valid character has been
detected.

<dt>[EINVAL]<dd>
There are insufficient arguments.

</dl>
<p>
In addition,
<i><a href="printf.html">printf()</a></i>
and
<i>fprintf()</i>
may fail if:
<dl compact>

<dt>[ENOMEM]<dd>
Insufficient storage space is available.

</dl>
</blockquote><h4><a name = "tag_000_008_809">&nbsp;</a>EXAMPLES</h4><blockquote>
To print the language-independent date and time format, the
following statement could be used:
<pre>
<code>
printf (format, weekday, month, day, hour, min);
</code>
</pre>
For American usage,
<i>format</i>
could be a pointer to the string:
<pre>
<code>
"%s, %s %d, %d:%.2d\n"
</code>
</pre>
producing the message:
<pre>
<code>
Sunday, July 3, 10:02
</code>
</pre>
whereas for German usage,
<i>format</i>
could be a pointer to the string:
<pre>
<code>
"%1$s, %3$d. %2$s, %4$d:%5$.2d\n"
</code>
</pre>
producing the message:
<pre>
<code>
Sonntag, 3. Juli, 10:02
</code>
</pre>
</blockquote><h4><a name = "tag_000_008_810">&nbsp;</a>APPLICATION USAGE</h4><blockquote>
If the application calling
<i>fprintf()</i>
has any objects of type
<b>wint_t</b>
or
<b>wchar_t,</b>
it must also include the header
<i><a href="wchar.h.html">&lt;wchar.h&gt;</a></i>
to have these objects defined.
</blockquote><h4><a name = "tag_000_008_811">&nbsp;</a>FUTURE DIRECTIONS</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_008_812">&nbsp;</a>SEE ALSO</h4><blockquote>
<i><a href="fputc.html">fputc()</a></i>,
<i><a href="fscanf.html">fscanf()</a></i>,
<i><a href="setlocale.html">setlocale()</a></i>,
<i><a href="wcrtomb.html">wcrtomb()</a></i>,
<i><a href="stdio.h.html">&lt;stdio.h&gt;</a></i>,
<i><a href="wchar.h.html">&lt;wchar.h&gt;</a></i>,
the <b>XBD</b> specification, <a href="../xbd/locale.html"><b>Locale</b>&nbsp;</a>,
<i><a href="http://www.opengroup.org/platform/resolutions/bwg98-006.html">Base Working Group Resolution # bwg98-006</a></i>.
</blockquote><h4>DERIVATION</h4><blockquote>
Derived from Issue 1 of the SVID.
</blockquote><hr size=2 noshade>
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Copyright &copy; 1997 The Open Group
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