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<TITLE>Defining Callback Functions</TITLE>
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<H2>37.1 Defining Callback Functions</H2>
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<P>The Standard Iostreams use callback functions to allow a program to respond to certain events. This allows programs to easily manage any dynamically allocated memory used by the stream objects. A program registers a callback by providing an ordinary function with an appropriate signature and calling <SAMP>ios_base::register_callback()</SAMP> with a pointer to the function and an index into the stream object's array of words. The registered callback function is then called any time one of the following occurs:</P>
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<LI><P CLASS="LIST">Destruction of a stream;<SAMP> std::ios_base::~ios_base()</SAMP> is called.</P></LI>
<LI><P CLASS="LIST">Imbuing a locale; <SAMP>std::ios_base::imbue()</SAMP> is called.</P></LI>
<LI><P CLASS="LIST">Copying the stream state; <SAMP>std::basic_ios&lt;&gt;::copyfmt()</SAMP> is called.</P></LI>
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