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| <H2>35.4 Implicit Synchronization by Tying Streams</H2> |
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| <P>Another mechanism for automatic synchronization in certain cases is tying a stream to an output stream, as demonstrated in the code below. All input or output operations flush the tied stream's buffer before they perform the actual operation.</P> |
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| <UL><PRE> |
| std::ofstream ostr("/tmp/fil"); |
| std::ifstream istr("/tmp/fil"); |
| std::ostream* old_tie = istr.tie(&ostr); //1 |
| |
| while (some_condition) { |
| ostr << "... some output ..."; |
| std::string s; |
| while (istr >> s) //2 |
| // process input ; |
| } |
| istr.tie(old_tie); //3 |
| </PRE></UL> |
| <TABLE CELLPADDING="3"> |
| |
| <TR VALIGN="top"><TD><SAMP>//1</SAMP></TD><TD>The input stream <SAMP>istr</SAMP> is tied to the output stream <SAMP>ostr</SAMP>. The <SAMP>tie()</SAMP> member function returns a pointer to the previously tied output stream, or <SAMP>0</SAMP> if no output stream is tied. |
| <TR VALIGN="top"><TD><SAMP>//2</SAMP></TD><TD>Before any input is done, the tied output stream's buffer is flushed so that the result of previous output operations to <SAMP>ostr</SAMP> is available in the external file <SAMP>/tmp/fil</SAMP>. |
| <TR VALIGN="top"><TD><SAMP>//3</SAMP></TD><TD>The previous tie is restored. |
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