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| <TITLE>The Predefined Streams</TITLE> |
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| <H2>28.1 The Predefined Streams</H2> |
| <A NAME="idx692"><!></A> |
| <A NAME="idx693"><!></A> |
| <P>There are eight predefined standard stream objects that are automatically created and initialized at program startup if the header <SAMP><iostream></SAMP> is included. These standard stream objects are associated with the C standard files <SAMP>stdin</SAMP>, <SAMP>stdout</SAMP>, and <SAMP>stderr</SAMP>, as shown in <A HREF="28-1.html#Table 26">Table 26</A>: </P> |
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| <H4><A NAME="Table 26">Table 26: Predefined standard streams with their associated C standard files</A></H4> |
| <TABLE BORDER="1" CELLPADDING="3" CELLSPACING="3"> |
| <tr><td valign=top><B>Narrow character<br> stream</B> |
| </td><td valign=top><B>Wide character<br> stream</B> |
| </td><td valign=top><B>Associated C standard<br> files</B> |
| </td></tr> |
| <tr><td valign=top><P CLASS="TABLE"><SAMP>cin</SAMP></P> |
| </td><td valign=top><P CLASS="TABLE"><SAMP>wcin</SAMP></P> |
| </td><td valign=top><P CLASS="TABLE"><SAMP>stdin</SAMP></P> |
| </td></tr> |
| <tr><td valign=top><P CLASS="TABLE"><SAMP>cout</SAMP></P> |
| </td><td valign=top><P CLASS="TABLE"><SAMP>wcout</SAMP></P> |
| </td><td valign=top><P CLASS="TABLE"><SAMP>stdout</SAMP></P> |
| </td></tr> |
| <tr><td valign=top><P CLASS="TABLE"><SAMP>cerr</SAMP></P> |
| </td><td valign=top><P CLASS="TABLE"><SAMP>wcerr</SAMP></P> |
| </td><td valign=top><P CLASS="TABLE"><SAMP>stderr</SAMP></P> |
| </td></tr> |
| <tr><td valign=top><P CLASS="TABLE"><SAMP>clog</SAMP></P> |
| </td><td valign=top><P CLASS="TABLE"><SAMP>wclog</SAMP></P> |
| </td><td valign=top><P CLASS="TABLE"><SAMP>stderr</SAMP></P> |
| </td></tr> |
| </TABLE> |
| <P>Like the C standard files, these stream objects are all associated by default with the terminal.</P> |
| <P>The difference between <SAMP>clog</SAMP> and <SAMP>cerr</SAMP> is that <SAMP>clog</SAMP> is fully buffered, whereas output to <SAMP>cerr</SAMP> is written to the external device after each formatting. With a fully buffered stream, output to the actual external device is written only when the buffer is full. Thus <SAMP>clog</SAMP> is more efficient for redirecting output to a file, while <SAMP>cerr</SAMP> is mainly useful for terminal I/O. Writing to the external device after every formatting, to the terminal in the case of <SAMP>cerr</SAMP>, serves the purpose of synchronizing output to and input from the terminal. Also, the predefined streams are synchronized with their associated C standard files. See <A HREF="35-6.html">Section 35.6</A> for details. </P> |
| <P>The standard stream objects are initialized in such a way that they can be used even in constructors and destructors of non-local objects with static storage duration. However, care must be taken to always include the header <SAMP><iostream></SAMP> prior to the definition of any such object.</P> |
| <P>Since the initialization of the standard iostream objects is a fairly resource-intensive operation it is not advisable to include the header <SAMP><iostream></SAMP> just as a convenience to gain access to either or both of <SAMP>basic_istream</SAMP> and <SAMP>basic_ostream</SAMP> in translation units that do not refer to the objects. In such cases, include the headers <SAMP><istream></SAMP> and <SAMP><ostream></SAMP> instead.</P> |
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