<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"> <html> <head> <meta NAME="AUTHOR" CONTENT="pme@gcc.gnu.org (Phil Edwards)"> <meta NAME="KEYWORDS" CONTENT="libstdc++, libstdc++-v3, GCC, g++"> <meta NAME="DESCRIPTION" CONTENT="Explanatory notes about libstdc++-v3."> <meta NAME="GENERATOR" CONTENT="vi and eight fingers"> <title>Explanatory notes about libstdc++-v3 design</title> <link REL=StyleSheet HREF="lib3styles.css"> <!-- $Id: explanations.html,v 1.1 2001/07/09 19:37:01 pme Exp $ --> </head> <body> <h1 CLASS="centered"><a name="top">Explanatory notes about libstdc++-v3 design</a></h1> <p>The latest version of this document is always available at <a href="http://gcc.gnu.org/onlinedocs/libstdc++/explanations.html"> http://gcc.gnu.org/onlinedocs/libstdc++/explanations.html</a>. </p> <p>To the <a href="http://gcc.gnu.org/libstdc++/">libstdc++-v3 homepage</a>. <!-- ####################################################### --> <hr> <a name="cstdio"><h3>"I/O packages", <code>--enable-cstdio</code></h3></a> <p>In addition to all the nifty things which C++ can do for I/O, its library also includes all of the I/O capabilites of C. Making them work together can be a challenge, not only <a href="27_io/howto.html#8">for the programmer</a> but for the implementors as well. </p> <p>There are two ways to do a C++ library: the cool way, and the easy way. More specifically, the cool-but-easy-to-get-wrong way, and the easy-to-guarantee-correct-behavior way. For 3.0, the easy way is used. </p> <p>Choosing 'stdio' is the easy way. It builds a C++ library which forwards all operations to the C library. Many of the C++ I/O functions are specified in the standard 'as if' they called a certain C function; the easiest way to get it correct is to actually call that function. The disadvantage is that the C++ code will run slower (fortunately, the layer is thin). </p> <p>Choosing 'libio' is the cool way; it allows C++ and C to share some buffers. It's disabled because of tricky synchronization issues. Other cool ways (various methods of sharing resources between C and C++ facilities, instead of layering) are possible. This approach can speed up I/O significantly. </p> <p>Other packages are possible. For a new package, a header must be written to provide types like streamsize (usually just a typedef), as well as some internal types like<code> __c_file_type </code> and <code> __c_lock </code> (for the stdio case, these are FILE (as in "FILE*") and a simple POSIX mutex, respectively). An interface class called <code> __basic_file </code> must also be filled in; as an example, for the stdio case, these member functions are all inline calles to fread, fwrite, etc. </p> <p>Return <a href="#top">to the top of the page</a> or <a href="http://gcc.gnu.org/libstdc++/">to the homepage</a>. </p> <!-- ####################################################### --> <hr> <P CLASS="fineprint"><em> $Id: explanations.html,v 1.1 2001/07/09 19:37:01 pme Exp $ </em></p> </body> </html>