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<H2>replace_if()</H2>
<P><B>Library:</B>&nbsp;&nbsp;<A HREF="2-9.html">Algorithms</A></P>

<PRE><HR><B><I>Function</I></B><HR></PRE>

<UL>
<LI><A HREF="#sec1">Local Index</A></LI>
<LI><A HREF="#sec2">Summary</A></LI>
<LI><A HREF="#sec3">Synopsis</A></LI>
<LI><A HREF="#sec4">Description</A></LI>
<LI><A HREF="#sec5">Complexity</A></LI>
<LI><A HREF="#sec6">Example</A></LI>
<LI><A HREF="#sec7">See Also</A></LI>
<LI><A HREF="#sec8">Standards Conformance</A></LI>
</UL>
<A NAME="sec1"><H3>Local Index</H3></A>
No Entries
<A NAME="sec2"><H3>Summary</H3></A>
<P>An algorithm that replaces elements in a collection with new values</P>
<A NAME="sec3"><H3>Synopsis</H3></A>

<PRE>#include &lt;algorithm&gt;

namespace std {
  template &lt;class ForwardIterator,
            class Predicate,
            class T&gt;
  void replace_if(ForwardIterator start,
                  ForwardIterator finish,
                  Predicate pred
                  const T&amp; new_value);
}
</PRE>
<A NAME="sec4"><H3>Description</H3></A>
<P>The <SAMP>replace_if()</SAMP> algorithm replaces element referred to by iterator <SAMP>i</SAMP> in the range<SAMP> [start, finish)</SAMP> with <SAMP>new_value</SAMP> when the following condition holds: <SAMP>pred(*i) == true</SAMP>. </P>
<A NAME="sec5"><H3>Complexity</H3></A>
<P>Exactly <SAMP>finish - start</SAMP> applications of the predicate are done.</P>
<A NAME="sec6"><H3>Example</H3></A>

<UL><PRE>//
//  replace.cpp
//

#include &lt;algorithm&gt;    // for replace, replace_if, replace_copy, ...
#include &lt;vector&gt;       // for vector
#include &lt;iterator&gt;     // for ostream_iterator
#include &lt;functional&gt;   // for not1, unary_function
#include &lt;iostream&gt;     // for cout, endl


struct is_prime: public std::unary_function&lt;short, bool&gt;
{
    bool operator() (const short&amp;) const;
};


bool is_prime::operator() (const short &amp;a) const
{
    // all primes smaller than 256
    static const unsigned short primes[] = {
        2, 3, 5, 7, 9, 11, 13, 15, 17, 19, 23, 25, 29, 31,
        35, 37, 41, 43, 47, 49, 53, 59, 61, 67, 71, 73, 79,
        83, 89, 97, 101, 103, 107, 109, 113, 121, 127, 131,
        137, 139, 143, 149, 151, 157, 163, 167, 169, 173, 179, 
        181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 
        241, 251
    };

    const unsigned short *end = primes + sizeof primes / 
                                         sizeof *primes;

    // search primes for a divisor
    for (const unsigned short *p = primes; p != end; ++p)
        if (0 == a % *p)
            return false;

    return 0 != a;
}


int main ()
{
    typedef std::vector&lt;short, std::allocator&lt;short&gt; &gt; Vector;
    typedef std::ostream_iterator&lt;short, char, 
                                  std::char_traits&lt;char&gt; &gt;
            Iter;

    // Populate a vector with arbitrary values.
    Vector v;
    for (Vector::value_type n = 11111; n != 11211; ++n)
        v.push_back (n);

    // Print out original vector.
    std::cout &lt;&lt; "Original sequence:\n    ";
    std::copy (v.begin (), v.end (), Iter (std::cout, " "));
    std::cout &lt;&lt; std::endl &lt;&lt; std::endl;

    // Replace one number with another.
    std::replace (v.begin (), v.end (), 11199, 11211);

    // Print out the new vector.
    std::cout &lt;&lt; "Sequence after replace:\n    ";
    std::copy (v.begin (), v.end (), Iter (std::cout, " "));
    std::cout &lt;&lt; std::endl &lt;&lt; std::endl;

    // Replace all numbers that aren't primes with zeros.
    std::replace_if (v.begin (), v.end (), 
                     std::not1 (is_prime ()), 0);

    // Print out the remaining vector.
    std::cout &lt;&lt; "After replace_if:\n    ";
    std::copy (v.begin (), v.end (), Iter (std::cout, " "));
    std::cout &lt;&lt; std::endl &lt;&lt; std::endl;

    // Replace zeros with ones.
    std::cout &lt;&lt; "Sequence replace_copy-ed to cout:\n    ";
    std::replace_copy (v.begin (), v.end (), 
                       Iter (std::cout, " "), 0, 1);
    std::cout &lt;&lt; std::endl &lt;&lt; std::endl;

    // A simple example of replace_copy_if.
    std::cout &lt;&lt; "Sequence replace_copy_if-ed to cout:\n    ";
    std::replace_copy_if (v.begin (), v.end (), 
                          Iter (std::cout, ""),
                          is_prime (), 1);
    std::cout &lt;&lt; std::endl;

    return 0;
}


Program Output:
Original sequence:
    11111 11112 11113 11114 11115 11116 11117 11118 11119
11120 11121 11122 11123 11124 11125 11126 11127 11128 11129
11130 11131 11132 11133 11134 11135 11136 11137 11138 11139
11140 11141 11142 11143 11144 11145 11146 11147 11148 11149
11150 11151 11152 11153 11154 11155 11156 11157 11158 11159
11160 11161 11162 11163 11164 11165 11166 11167 11168 11169
11170 11171 11172 11173 11174 11175 11176 11177 11178 11179
11180 11181 11182 11183 11184 11185 11186 11187 11188 11189
11190 11191 11192 11193 11194 11195 11196 11197 11198 11199
11200 11201 11202 11203 11204 11205 11206 11207 11208 11209
11210 

Sequence after replace:
    11111 11112 11113 11114 11115 11116 11117 11118 11119
11120 11121 11122 11123 11124 11125 11126 11127 11128 11129
11130 11131 11132 11133 11134 11135 11136 11137 11138 11139
11140 11141 11142 11143 11144 11145 11146 11147 11148 11149
11150 11151 11152 11153 11154 11155 11156 11157 11158 11159
11160 11161 11162 11163 11164 11165 11166 11167 11168 11169
11170 11171 11172 11173 11174 11175 11176 11177 11178 11179
11180 11181 11182 11183 11184 11185 11186 11187 11188 11189
11190 11191 11192 11193 11194 11195 11196 11197 11198 11211
11200 11201 11202 11203 11204 11205 11206 11207 11208 11209
11210 

After replace_if:
    0 0 11113 0 0 0 11117 0 11119 0 0 0 0 0 0 0 0 0 0 0 11131
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 11149 0 0 0 0 0 0 0 0 0
11159 0 11161 0 0 0 0 0 0 0 0 0 11171 0 11173 0 0 0 11177 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 11197 0 0 0 0 0 0 0 0 0 0 0
0 0

Sequence replace_copy-ed to cout:
    1 1 11113 1 1 1 11117 1 11119 1 1 1 1 1 1 1 1 1 1 1 11131
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11149 1 1 1 1 1 1 1 1 1
11159 1 11161 1 1 1 1 1 1 1 1 1 11171 1 11173 1 1 1 11177 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11197 1 1 1 1 1 1 1 1 1 1 1
1 1

Sequence replace_copy_if-ed to cout:
    00100010100000000000100000000000000000100000000010100000000010
10001000000000000000000010000000000000
</PRE></UL>
<UL><PRE></PRE></UL>
<A NAME="sec7"><H3>See Also</H3></A>
<P><SAMP><A HREF="replace.html">replace()</A></SAMP>, <SAMP><A HREF="replace-copy.html">replace_copy()</A></SAMP>, <SAMP><A HREF="replace-copy-if.html">replace_copy_if()</A></SAMP></P>
<A NAME="sec8"><H3>Standards Conformance</H3></A>
<P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 25.2.4</I></P>

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