diff options
Diffstat (limited to 'gcc-4.4.3/libstdc++-v3/doc/html/manual/fstreams.html')
| -rw-r--r-- | gcc-4.4.3/libstdc++-v3/doc/html/manual/fstreams.html | 52 |
1 files changed, 52 insertions, 0 deletions
diff --git a/gcc-4.4.3/libstdc++-v3/doc/html/manual/fstreams.html b/gcc-4.4.3/libstdc++-v3/doc/html/manual/fstreams.html new file mode 100644 index 000000000..aaa0c88f9 --- /dev/null +++ b/gcc-4.4.3/libstdc++-v3/doc/html/manual/fstreams.html @@ -0,0 +1,52 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter 27. File Based Streams</title><meta name="generator" content="DocBook XSL Stylesheets V1.74.0" /><meta name="keywords" content=" ISO C++ , library " /><link rel="home" href="../spine.html" title="The GNU C++ Library Documentation" /><link rel="up" href="io.html" title="Part XI. Input and Output" /><link rel="prev" href="stringstreams.html" title="Chapter 26. Memory Based Streams" /><link rel="next" href="bk01pt11ch27s02.html" title="Binary Input and Output" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 27. File Based Streams</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="stringstreams.html">Prev</a> </td><th width="60%" align="center">Part XI. + Input and Output + +</th><td width="20%" align="right"> <a accesskey="n" href="bk01pt11ch27s02.html">Next</a></td></tr></table><hr /></div><div class="chapter" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title"><a id="manual.io.filestreams"></a>Chapter 27. File Based Streams</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="fstreams.html#manual.io.filestreams.copying_a_file">Copying a File</a></span></dt><dt><span class="sect1"><a href="bk01pt11ch27s02.html">Binary Input and Output</a></span></dt><dt><span class="sect1"><a href="bk01pt11ch27s03.html">More Binary Input and Output</a></span></dt></dl></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="manual.io.filestreams.copying_a_file"></a>Copying a File</h2></div></div></div><p> + </p><p>So you want to copy a file quickly and easily, and most important, + completely portably. And since this is C++, you have an open + ifstream (call it IN) and an open ofstream (call it OUT): + </p><pre class="programlisting"> + #include <fstream> + + std::ifstream IN ("input_file"); + std::ofstream OUT ("output_file"); </pre><p>Here's the easiest way to get it completely wrong: + </p><pre class="programlisting"> + OUT << IN;</pre><p>For those of you who don't already know why this doesn't work + (probably from having done it before), I invite you to quickly + create a simple text file called "input_file" containing + the sentence + </p><pre class="programlisting"> + The quick brown fox jumped over the lazy dog.</pre><p>surrounded by blank lines. Code it up and try it. The contents + of "output_file" may surprise you. + </p><p>Seriously, go do it. Get surprised, then come back. It's worth it. + </p><p>The thing to remember is that the <code class="code">basic_[io]stream</code> classes + handle formatting, nothing else. In particular, they break up on + whitespace. The actual reading, writing, and storing of data is + handled by the <code class="code">basic_streambuf</code> family. Fortunately, the + <code class="code">operator<<</code> is overloaded to take an ostream and + a pointer-to-streambuf, in order to help with just this kind of + "dump the data verbatim" situation. + </p><p>Why a <span class="emphasis"><em>pointer</em></span> to streambuf and not just a streambuf? Well, + the [io]streams hold pointers (or references, depending on the + implementation) to their buffers, not the actual + buffers. This allows polymorphic behavior on the part of the buffers + as well as the streams themselves. The pointer is easily retrieved + using the <code class="code">rdbuf()</code> member function. Therefore, the easiest + way to copy the file is: + </p><pre class="programlisting"> + OUT << IN.rdbuf();</pre><p>So what <span class="emphasis"><em>was</em></span> happening with OUT<<IN? Undefined + behavior, since that particular << isn't defined by the Standard. + I have seen instances where it is implemented, but the character + extraction process removes all the whitespace, leaving you with no + blank lines and only "Thequickbrownfox...". With + libraries that do not define that operator, IN (or one of IN's + member pointers) sometimes gets converted to a void*, and the output + file then contains a perfect text representation of a hexadecimal + address (quite a big surprise). Others don't compile at all. + </p><p>Also note that none of this is specific to o<span class="emphasis"><em>*f*</em></span>streams. + The operators shown above are all defined in the parent + basic_ostream class and are therefore available with all possible + descendants. + </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="stringstreams.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="io.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="bk01pt11ch27s02.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 26. Memory Based Streams </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> Binary Input and Output</td></tr></table></div></body></html> |