istream.html

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<P>The function:</P>

<PRE>istream&amp; <B>operator&gt;&gt;</B>(bool&amp; val);</PRE>

<P>extracts a field and converts it to a boolean value.
The function endeavors to match a complete, nonempty
<B><A NAME="boolean input field">boolean input field</A></B>.
If successful it converts
the boolean input field to a value of type <CODE>bool</CODE>
and stores that value in <CODE>val</CODE>.</P>

<P>A boolean input field takes one of two forms.
If <CODE><A HREF="ios.html#ios_base::flags">flags</A>() &amp;
ios_base::<A HREF="ios.html#ios_base::boolalpha">boolalpha</A></CODE>
is false, it is the same as an
<A HREF="#integer input field">integer input field</A>, except that the
converted value must be either 0 (for false) or 1 (for true).
Otherwise, the sequence must match either
<CODE>false</CODE> (for false), or
<CODE>true</CODE> (for true).
The function returns <CODE>*this</CODE>.</P>


<P>The functions:</P>

<PRE>istream&amp; <B>operator&gt;&gt;</B>(short&amp; val);
istream&amp; <B>operator&gt;&gt;</B>(unsigned short&amp; val);
istream&amp; <B>operator&gt;&gt;</B>(int&amp; val);
istream&amp; <B>operator&gt;&gt;</B>(unsigned int&amp; val);
istream&amp; <B>operator&gt;&gt;</B>(long&amp; val);
istream&amp; <B>operator&gt;&gt;</B>(unsigned long&amp; val);
istream&amp; <B>operator&gt;&gt;</B>(void *&amp; val);</PRE>

<P>each extract a field and convert it to a numeric value.
Each function endeavors to match a complete, nonempty
<B><A NAME="integer input field">integer input field</A></B>.
If successful, it stores the result in <CODE>val</CODE>.
Otherwise, the function stores nothing in <CODE>val</CODE> and calls
<CODE><A HREF="ios.html#ios::setstate">setstate</A>(ios_base::failbit)</CODE>.
If the function encounters end of file, it calls
<CODE>setstate(ios_base::eofbit)</CODE>.</P>

<P>The integer input field is converted by the same rules used by the
<A HREF="lib_scan.html#Scan Functions">scan functions</A>
for matching and converting a series of <I>char</I> elements from a file.
The equivalent
<A HREF="lib_scan.html#scan conversion specification">scan conversion
specification</A> is determined as follows:</P>

<UL>
<LI>If <CODE><A HREF="ios.html#ios_base::flags">flags</A>() &amp;
ios_base::<A HREF="ios.html#ios_base::basefield">basefield</A> ==
ios_base::<A HREF="ios.html#ios_base::oct">oct</A></CODE>, the
conversion specification is <CODE>lo</CODE>.</LI>

<LI>If <CODE>flags() &amp; ios_base::basefield ==
ios_base::<A HREF="ios.html#ios_base::hex">hex</A></CODE>, the
conversion specification is <CODE>lx</CODE>.</LI>

<LI>If <CODE>flags() &amp; ios_base::basefield == 0</CODE>, the
conversion specification is <CODE>li</CODE>.</LI>

<LI>Otherwise, the conversion specification is <CODE>ld</CODE>
if <CODE>val</CODE> has a signed type, <CODE>lu</CODE> if <CODE>val</CODE>
has an unsigned type, or <CODE>p</CODE> if <CODE>val</CODE> has type
<CODE>void *</CODE>.</LI>
</UL>

<P>If the converted value cannot
be represented as the type of <CODE>val</CODE>, the function calls
<CODE><A HREF="ios.html#ios::setstate">setstate</A>(failbit)</CODE>.
In any case, the function returns <CODE>*this</CODE>.</P>

<P>The functions:</P>

<PRE>istream&amp; <B>operator&gt;&gt;</B>(float&amp; val);
istream&amp; <B>operator&gt;&gt;</B>(double&amp; val);
istream&amp; <B>operator&gt;&gt;</B>(long double&amp; val);</PRE>

<P>each extract a field and convert it to a numeric value.
Each function endeavors to match a complete, nonempty
A period (<CODE>.</CODE>) separates the integer digits from the
fraction digits.
The equivalent scan conversion specifier is <CODE>f</CODE>
if <CODE>val</CODE> has type <I>float,</I> <CODE>lf</CODE> if <CODE>val</CODE>
has type <I>double,</I> or <CODE>Lf</CODE> if <CODE>val</CODE> has type
<I>long double.</I></P>

<P>If the converted value cannot
be represented as the type of <CODE>val</CODE>, the function calls
<CODE><A HREF="ios.html#ios::setstate">setstate</A>(failbit)</CODE>.
In any case, it returns <CODE>*this</CODE>.</P>

<H3><A NAME="istream::peek"><CODE>istream::peek</CODE></A></H3>

<PRE>int_type <B>peek</B>();</PRE>

<P>The <A HREF="#unformatted input functions">unformatted input function</A>
extracts an element, if possible, as if by returning
<CODE>rdbuf()-&gt;<A HREF="streambu.html#streambuf::sgetc">sgetc</A>()</CODE>.
Otherwise, it returns
<CODE>traits_type::<A HREF="string2.html#char_traits::eof">eof</A>()</CODE>.</P>

<H3><A NAME="istream::putback"><CODE>istream::putback</CODE></A></H3>

<PRE>istream&amp; <B>putback</B>(char_type ch);</PRE>

<P>The <A HREF="#unformatted input functions">unformatted input function</A>
puts back <CODE>ch</CODE>, if possible, as if by calling
<CODE>rdbuf()-&gt;<A HREF="streambu.html#streambuf::sputbackc">sputbackc</A>()</CODE>.
If <CODE><A HREF="ios.html#ios::rdbuf">rdbuf</A>()</CODE>
is a null pointer, or if the call to <CODE>sputbackc</CODE> returns
<CODE>traits_type::<A HREF="string2.html#char_traits::eof">eof</A>()</CODE>,
the function calls
<CODE><A HREF="ios.html#ios::setstate">setstate</A>(badbit)</CODE>.
In any case, it returns <CODE>*this</CODE>.</P>

<H3><A NAME="istream::read"><CODE>istream::read</CODE></A></H3>

<PRE>istream&amp; <B>read</B>(char_type *str, streamsize count);</PRE>

<P>The <A HREF="#unformatted input functions">unformatted input function</A>
extracts up to <CODE>count</CODE> elements
and stores them in the array beginning at <CODE>str</CODE>.
Extraction stops early on end-of-file, in which case the function calls
<CODE><A HREF="ios.html#ios::setstate">setstate</A>(failbit)</CODE>.
In any case, it returns <CODE>*this</CODE>.</P>

<H3><A NAME="istream::readsome"><CODE>istream::readsome</CODE></A></H3>

<PRE>streamsize <B>readsome</B>(char_type *str, streamsize count);</PRE>

<P>The <A HREF="#unformatted input functions">unformatted input function</A>
extracts up to <CODE>count</CODE> elements
and stores them in the array beginning at <CODE>str</CODE>.
If <CODE><A HREF="ios.html#ios::good">good</A>()</CODE> is
false, the function calls
<CODE><A HREF="ios.html#ios::setstate">setstate</A>(failbit)</CODE>.
Otherwise, it assigns the value of
<CODE>rdbuf()-&gt;<A HREF="streambu.html#streambuf::in_avail">in_avail</A>()</CODE>
to <CODE>N</CODE>. If <CODE>N &lt; 0</CODE>, the function calls
<CODE><A HREF="ios.html#ios::setstate">setstate</A>(eofbit)</CODE>.
Otherwise, it replaces the value stored in <CODE>N</CODE> with
the smaller of <CODE>count</CODE> and <CODE>N</CODE>, then calls
<CODE><A HREF="#istream::read">read</A>(str, N)</CODE>.
In any case, the function returns
<CODE><A HREF="#istream::gcount">gcount</A>()</CODE>.</P>

<H3><A NAME="istream::seekg"><CODE>istream::seekg</CODE></A></H3>

<PRE>istream&amp; <B>seekg</B>(pos_type pos);
istream&amp; <B>seekg</B>(off_type off,
    ios_base::seek_dir way);</PRE>

<P>If <CODE><A HREF="ios.html#ios::fail">fail</A>()</CODE> is false,
the first member function calls
<CODE>newpos = <A HREF="ios.html#ios::rdbuf">rdbuf</A>()-&gt;
<A HREF="streambu.html#streambuf::pubseekpos">pubseekpos</A>(pos,
<A HREF="ios.html#ios_base::in">in</A>)</CODE>,
for some <CODE>pos_type</CODE> temporary object <CODE>newpos</CODE>.
If <CODE>fail()</CODE> is false, the second function calls
<CODE>newpos = rdbuf()-&gt;
<A HREF="streambu.html#streambuf::pubseekoff">pubseekoff</A>(off, way,
<A HREF="ios.html#ios_base::in">in</A>)</CODE>.
In either case, if <CODE>(off_type)newpos == (off_type)(-1)</CODE>
(the positioning operation fails) the function calls
<CODE>istr.<A HREF="ios.html#ios::setstate">setstate</A>(failbit)</CODE>.
Both functions return <CODE>*this</CODE>.</P>

<H3><A NAME="istream::sentry"><CODE>istream::sentry</CODE></A></H3>

<PRE>class <B>sentry</B> {
public:
    explicit <B>sentry</B>(istream&lt;Elem, Tr&gt;&amp; istr,
        bool noskip = false);
    <B>operator bool</B>() const;
    };</PRE>

<P>The nested class describes an object whose declaration structures the
<A HREF="#formatted input functions">formatted input functions</A> and the
<A HREF="#unformatted input functions">unformatted input functions</A>.
If <CODE>istr.<A HREF="ios.html#ios::good">good</A>()</CODE>
is true, the constructor:</P>

<UL>
<LI>calls <CODE>istr.<A HREF="ios.html#ios::tie">tie</A>-&gt;
<A HREF="ostream.html#ostream::flush">flush</A>()</CODE>
if <CODE>istr.tie()</CODE> is not a null pointer</LI>

<LI>effectively calls <CODE><A HREF="#ws">ws</A>(istr)</CODE> if
<CODE>istr.<A HREF="ios.html#ios_base::flags">flags</A>() &amp;
<A HREF="ios.html#ios_base::skipws">skipws</A></CODE> is nonzero</LI>
</UL>

<P>If, after any such preparation,
<CODE>istr.good()</CODE> is false, the constructor calls
<CODE>istr.<A HREF="ios.html#ios::setstate">setstate</A>(failbit)</CODE>.
In any case, the constructor stores the value returned by <CODE>istr.good()</CODE>
in <B>status</B>.
A later call to <CODE>operator bool()</CODE> delivers this stored value.</P>

<H3><A NAME="istream::sync"><CODE>istream::sync</CODE></A></H3>

<PRE>int <B>sync</B>();</PRE>

<P>If <CODE><A HREF="ios.html#ios::rdbuf">rdbuf</A>()</CODE> is
a null pointer, the function returns -1. Otherwise, it calls
<CODE>rdbuf()-&gt;<A HREF="streambu.html#streambuf::pubsync">pubsync</A>()</CODE>.
If that returns -1, the function calls
<CODE><A HREF="ios.html#ios::setstate">setstate</A>(badbit)</CODE>
and returns -1. Otherwise, the function returns zero.</P>

<H3><A NAME="istream::tellg"><CODE>istream::tellg</CODE></A></H3>

<PRE>pos_type <B>tellg</B>();</PRE>

<P>If <CODE><A HREF="ios.html#ios::fail">fail</A>()</CODE> is false,
the member function returns
<CODE><A HREF="ios.html#ios::rdbuf">rdbuf</A>()-&gt;
<A HREF="streambu.html#streambuf::pubseekoff">pubseekoff</A>(0,
<A HREF="ios.html#ios_base::cur">cur</A>,
<A HREF="ios.html#ios_base::in">in</A>)</CODE>.
Otherwise, it returns <CODE>pos_type(-1)</CODE>.</P>

<H3><A NAME="istream::unget"><CODE>istream::unget</CODE></A></H3>

<PRE>istream&amp; <B>unget</B>();</PRE>

<P>The <A HREF="#unformatted input functions">unformatted input function</A>
puts back the previous element in the stream, if possible, as if by calling
<CODE>rdbuf()-&gt;<A HREF="streambu.html#streambuf::sungetc">sungetc</A>()</CODE>.
If <CODE><A HREF="ios.html#ios::rdbuf">rdbuf</A>()</CODE>
is a null pointer, or if the call to <CODE>sungetc</CODE> returns
<CODE>traits_type::<A HREF="string2.html#char_traits::eof">eof</A>()</CODE>,
the function calls
<CODE><A HREF="ios.html#ios::setstate">setstate</A>(badbit)</CODE>.
In any case, it returns <CODE>*this</CODE>.</P>


<H2><A NAME="operator&gt;&gt;"><CODE>operator&gt;&gt;</CODE></A></H2>

<PRE>istream&amp;
    <B>operator&gt;&gt;</B>(istream&amp; istr, char *str);
istream&amp;
    <B>operator&gt;&gt;</B>(istream&amp; istr, char&amp; ch);
istream&amp;
    <B>operator&gt;&gt;</B>(istream&amp; istr, signed char *str);
istream&amp;
    <B>operator&gt;&gt;</B>(istream&amp; istr, signed char&amp; ch);
istream&amp;
    <B>operator&gt;&gt;</B>(istream&amp; istr, unsigned char *str);
istream&amp;
    <B>operator&gt;&gt;</B>(istream istr, unsigned char&amp; ch);</PRE>

<P>All of these functions are
<A HREF="#formatted input functions">formatted input functions</A>.
The function:</P>

<PRE>istream&amp;
    <B>operator&gt;&gt;</B>(istream&amp; istr, char *str);</PRE>

<P>extracts up to <CODE>N - 1</CODE> elements
and stores them in the array beginning at <CODE>str</CODE>.
If <CODE>istr.<A HREF="ios.html#ios_base::width">width</A>()</CODE> is greater
than zero, <CODE>N</CODE> is <CODE>istr.width()</CODE>; otherwise it is
the size of
the largest array of <I>char</I> that can be declared.
The function always stores
<CODE>char(0)</CODE> after
any extracted elements it stores. Extraction stops early on end-of-file,
on a character with value <CODE>char(0)</CODE> (which is not extracted),
or on any element (which is not extracted) that would be discarded by
<CODE><A HREF="#ws">ws</A></CODE>.
If the function extracts no elements, it calls
<CODE>istr.<A HREF="ios.html#ios::setstate">setstate</A>(failbit)</CODE>.
In any case, it calls <CODE>istr.width(0)</CODE> and
returns <CODE>istr</CODE>.</P>

<P>The function:</P>

<PRE>istream&amp;
    <B>operator&gt;&gt;</B>(istream&amp; istr, char&amp; ch);</PRE>

<P>extracts an element, if possible, and stores it in <CODE>ch</CODE>.
Otherwise, it calls
<CODE>is.<A HREF="ios.html#ios::setstate">setstate</A>(failbit)</CODE>.
In any case, it returns <CODE>istr</CODE>.</P>

<P>The function:</P>

<PRE>istream&amp;
    <B>operator&gt;&gt;</B>(istream&amp; istr, signed char *str);</PRE>

<P>returns <CODE>istr &gt;&gt; (char *)str</CODE>.</P>

<P>The function:</P>

<PRE>istream&amp;
    <B>operator&gt;&gt;</B>(istream&amp; istr, signed char&amp; ch);</PRE>

<P>returns <CODE>istr &gt;&gt; (char&amp;)ch</CODE>.</P>

<P>The function:</P>

<PRE>istream&amp;
    <B>operator&gt;&gt;</B>(istream&amp; istr, unsigned char *str);</PRE>

<P>returns <CODE>istr &gt;&gt; (char *)str</CODE>.</P>

<P>The function:</P>

<PRE>istream&amp;
    <B>operator&gt;&gt;</B>(istream&amp; istr, unsigned char&amp; ch);</PRE>

<P>returns <CODE>istr &gt;&gt; (char&amp;)ch</CODE>.</P>


<H2><A NAME="ws"><CODE>ws</CODE></A></H2>

<PRE>istream&amp; <B>ws</B>(istream&amp; istr);</PRE>

<P>The manipulator extracts and discards any elements
<CODE>ch</CODE> for which
<CODE><A HREF="ctype.html#isspace">isspace</A>(ch)</CODE>
is true.</P>

<P>The function calls
<CODE><A HREF="ios.html#ios::setstate">setstate</A>(eofbit)</CODE>
if it encounters end-of-file while extracting elements.
It returns <CODE>istr</CODE>.</P>

<HR>
<P>See also the
<B><A HREF="index.html#Table of Contents">Table of Contents</A></B> and the
<B><A HREF="_index.html">Index</A></B>.</P>

<P><I>
<A HREF="crit_pjp.html">Copyright</A> &#169; 1992-2002
by P.J. Plauger. All rights reserved.</I></P>

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