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| <H2>22.2 Declaring a valarray</H2> |
| <A NAME="idx460"><!></A> |
| <P>A <B><I><A HREF="../stdlibref/valarray.html">valarray</A></I></B> can be constructed by any of the following means:</P> |
| <UL> |
| <LI><P CLASS="LIST"><B>Default constructor</B>. The default constructor is provided to allow arrays of <B><I><A HREF="../stdlibref/valarray.html">valarray</A></I></B>s. Use the resize function to adjust the <B><I>valarray</I></B> after construction.</P></LI> |
| <LI><P CLASS="LIST"><B>Construction and initialization.</B> A <B><I><A HREF="../stdlibref/valarray.html">valarray</A></I></B> provides two ways to start with a given size and values: </P></LI> |
| <UL> |
| <LI><P CLASS="LIST"><SAMP>valarray(const T& v,size_t n)</SAMP> constructs a <B><I><A HREF="../stdlibref/valarray.html">valarray</A></I></B> of size <SAMP>n</SAMP> with each element initialized to the value <SAMP>v</SAMP>. </P></LI> |
| <LI><P CLASS="LIST"><SAMP>valarray(const T* p,size_t n)</SAMP> constructs a <B><I><A HREF="../stdlibref/valarray.html">valarray</A></I></B> of size <SAMP>n</SAMP> with each element initialized to the corresponding element of the array pointed to by <SAMP>p</SAMP>. This constructor allows a program to transfer data with maximum efficiency from an ordinary `C' array (resulting from a file operation, for example) into a <B><I>valarray</I></B>.</P></LI> |
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| <LI><P CLASS="LIST"><B>Copy constructor</B>. The copy constructor has value semantics.</P></LI> |
| <LI><P CLASS="LIST"><B>Conversion constructors</B>. Class <B><I><A HREF="../stdlibref/valarray.html">valarray</A></I></B> provides four conversion constructors for converting from auxiliary classes generated by subscript operations. We'll look at these classes in detail and describe the use of the conversion constructors in <A HREF="22-4.html#2242">Section 22.4.2</A>.</P></LI> |
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| <P>The following example shows the use of the first three categories of constructors:</P> |
| |
| <UL><PRE> |
| #include <valarray> |
| |
| std::valarray<int> v1; // construct an empty valarray |
| std::valarray<int> v2(1,3); // construct a valarray of three |
| // elements, all initialized to 1 |
| v1.resize(3,2); // resize the first valarray to three |
| // elements, all initialized to 2 |
| std::valarray<int> v3(v1); // v3 gets a copy of v1's elements. |
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