fscanf.html

unix 下的C开发手册,还用详细的例程。

If an l (ell) qualifier is present, the input is a sequence of
characters that begins in the initial shift state.  Each
character is converted to a wide-character as if by a call
to the
<i><a href="mbrtowc.html">mbrtowc()</a></i>
function, with the conversion state described by an
<b>mbstate_t</b>
object initialised to zero before the first character is
converted.  The corresponding argument must be a pointer to an array
of
<b>wchar_t</b>
large enough to accept the sequence and the terminating null 
wide-character, which will be added automatically.

<dt>[<dd>Matches a non-empty sequence of bytes from a set of expected
bytes (the
<i>scanset</i>).
The normal skip over white-space characters is suppressed in this case.
The corresponding argument must be a pointer to the initial
byte of an array of
<b>char</b>,
<b>signed char</b>
or
<b>unsigned char</b>
large enough to accept the sequence and a
terminating null byte, which will be added automatically.

If an l (ell) qualifier is present, the input is a sequence of
characters that begins in the initial shift state.  Each
character in the sequence is converted to a wide-character
as if by a call to the
<i><a href="mbrtowc.html">mbrtowc()</a></i>
function, with the conversion state described by an
<b>mbstate_t</b>
object initialised to zero before the first character is
converted.  The corresponding argument must be a pointer to an array
of
<b>wchar_t</b>
large enough to accept the sequence and the terminating null
wide-character, which will be added automatically.

The conversion specification includes all subsequent bytes in
the
<i>format</i>
string up to and including the matching right square bracket (]).
The bytes between the square brackets (the
<i>scanlist</i>)
comprise the scanset, unless the byte after the left square bracket
is a circumflex (^), in which case the scanset contains all
bytes that do not appear in the scanlist between the
circumflex and the right square bracket.
If the conversion specification begins with []
or [^], the right square bracket is included in the scanlist and the
next right square bracket is the matching right square bracket that ends the
conversion specification; otherwise the first right square bracket is the
one that ends the conversion specification.
If a - is in the scanlist and is not the first character, nor the second
where the first character is a ^, nor the last character,
the behaviour is implementation-dependent.

<dt>c<dd>Matches a sequence of bytes of the number specified by the
field width (1 if no field width is present in the conversion specification).
The corresponding argument must be a pointer to the initial
byte of an array of <b>char</b>, <b>signed&nbsp;char</b> or <b>unsigned char</b>
large enough to accept the sequence.
No null byte is added.
The normal skip over white-space characters is suppressed in this case.

If an l (ell) qualifier is present, the input is a sequence of
characters that begins in the initial shift state.  Each
character in the sequence is converted to a wide-character
as if by a call to the
<i><a href="mbrtowc.html">mbrtowc()</a></i>
function, with the conversion state described by an
<b>mbstate_t</b>
object initialised to zero before the first character is
converted.  The corresponding argument must be a pointer to an array
of
<b>wchar_t</b>
large enough to accept the resulting sequence of wide-characters.  No
null wide-character is added.

<dt>p<dd>Matches an implementation-dependent set of sequences, which must
be the same as the set of sequences that is produced by the %p
conversion of the corresponding
<i><a href="fprintf.html">fprintf()</a></i>
functions.
The corresponding argument must be a pointer to a pointer to
<b>void</b>.
The interpretation of the input item is implementation-dependent.
If the input item is a value converted earlier during the
same program execution, the pointer that results will compare equal
to that value; otherwise the behaviour of the %p conversion is undefined.

<dt>n<dd>No input is consumed.
The corresponding argument must be a pointer to
the integer into which is to be written the number of
bytes read from the input so far by this call to the
<i>fscanf()</i>
functions.
Execution of a %n
conversion specification
does not increment the assignment count returned at the
completion of execution of the function.

<dt>C<dd>Same as lc.

<dt>S<dd>Same as ls.

<dt>%<dd>Matches a single %;
no conversion or assignment occurs.
The complete conversion specification must be %%.

</dl>
<p>
If a conversion specification is invalid, the behaviour is
undefined.
<p>
The conversion characters E, G and X
are also valid and behave the same as, respectively, e, g and x.
<p>
If end-of-file is encountered during input, conversion is terminated.
If end-of-file occurs before any bytes matching the current
conversion specification (except for
%n) have been read
(other than leading white-space characters, where
permitted), execution of the current conversion specification
terminates with an
input failure.  Otherwise, unless execution of the current
conversion specification is terminated with a matching failure,
execution of the following conversion specification (if any)
is terminated with an input failure.
<p>
Reaching the end of the string in
<i>sscanf()</i>
is equivalent to encountering end-of-file for
<i>fscanf()</i>.
<p>
If conversion terminates on a conflicting input, the
offending input is left unread in the input.
Any trailing white space (including newline characters) is left
unread unless matched by a conversion specification.
The success of literal matches and suppressed assignments is only
directly determinable via the %n conversion specification.
<p>
The
<i>fscanf()</i>
and
<i>scanf()</i>
functions may mark the
<i>st_atime</i>
field of the file associated with
<i>stream</i>
for update.
The
<i>st_atime</i>
field will be marked for update by the first successful execution of
<i><a href="fgetc.html">fgetc()</a></i>,
<i><a href="fgets.html">fgets()</a></i>,
<i><a href="fread.html">fread()</a></i>,
<i><a href="getc.html">getc()</a></i>,
<i><a href="getchar.html">getchar()</a></i>,
<i><a href="gets.html">gets()</a></i>,
<i>fscanf()</i>
or
<i>fscanf()</i>
using
<i>stream</i>
that returns data not supplied by a prior call to
<i><a href="ungetc.html">ungetc()</a></i>.
</blockquote><h4><a name = "tag_000_005_269">&nbsp;</a>RETURN VALUE</h4><blockquote>
Upon successful completion, these functions return the number of successfully
matched and assigned input items; this number can be 0 in the event of an
early matching failure.  If the input ends before the first matching failure
or conversion, EOF is returned.  If a read error occurs the error indicator
for the stream is set, EOF is returned, and
<i>errno</i>
is set to indicate the error.
</blockquote><h4><a name = "tag_000_005_270">&nbsp;</a>ERRORS</h4><blockquote>
For the conditions under which the
<i>fscanf()</i>
functions will fail and may fail, refer to
<i><a href="fgetc.html">fgetc()</a></i>
or
<i><a href="fgetwc.html">fgetwc()</a></i>.
<p>
In addition,
<i>fscanf()</i>
may fail if:
<dl compact>

<dt>[EILSEQ]<dd>
Input byte sequence does not form a valid character.

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

</dl>
</blockquote><h4><a name = "tag_000_005_271">&nbsp;</a>EXAMPLES</h4><blockquote>
The call:
<pre>
<code>
int i, n; float x; char name[50];
n = scanf("%d%f%s", &amp;i, &amp;x, name);
</code>
</pre>
with the input line:
<pre>
<code>
25 54.32E-1 Hamster
</code>
</pre>
will assign to
<i>n</i>
the value 3, to
<i>i</i>
the value 25, to
<i>x</i>
the value 5.432, and
<i>name</i>
will contain the string Hamster.
<p>
The call:
<pre>
<code>
int i; float x; char name[50];
(void) scanf("%2d%f%*d %[0123456789]", &amp;i, &amp;x, name);
</code>
</pre>
with input:
<pre>
<code>
56789 0123 56a72
</code>
</pre>
<p>
will assign 56 to
<i>i</i>,
789.0 to
<i>x</i>,
skip 0123, and place the string 56\0 in
<i>name</i>.
The next call to
<i><a href="getchar.html">getchar()</a></i>
will return the character a.
</blockquote><h4><a name = "tag_000_005_272">&nbsp;</a>APPLICATION USAGE</h4><blockquote>
If the application calling
<i>fscanf()</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_005_273">&nbsp;</a>FUTURE DIRECTIONS</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_005_274">&nbsp;</a>SEE ALSO</h4><blockquote>
<i><a href="getc.html">getc()</a></i>,
<i><a href="printf.html">printf()</a></i>,
<i><a href="setlocale.html">setlocale()</a></i>,
<i><a href="strtod.html">strtod()</a></i>,
<i><a href="strtol.html">strtol()</a></i>,
<i><a href="strtoul.html">strtoul()</a></i>,
<i><a href="wcrtomb.html">wcrtomb()</a></i>,
<i><a href="langinfo.h.html">&lt;langinfo.h&gt;</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>.
</blockquote><h4>DERIVATION</h4><blockquote>
Derived from Issue 1 of the SVID.
</blockquote><hr size=2 noshade>
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