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| author | upstream source tree <ports@midipix.org> | 2015-03-15 20:14:05 -0400 |
|---|---|---|
| committer | upstream source tree <ports@midipix.org> | 2015-03-15 20:14:05 -0400 |
| commit | 554fd8c5195424bdbcabf5de30fdc183aba391bd (patch) | |
| tree | 976dc5ab7fddf506dadce60ae936f43f58787092 /libstdc++-v3/doc/html/manual/containers_and_c.html | |
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Diffstat (limited to 'libstdc++-v3/doc/html/manual/containers_and_c.html')
| -rw-r--r-- | libstdc++-v3/doc/html/manual/containers_and_c.html | 90 |
1 files changed, 90 insertions, 0 deletions
diff --git a/libstdc++-v3/doc/html/manual/containers_and_c.html b/libstdc++-v3/doc/html/manual/containers_and_c.html new file mode 100644 index 000000000..3e612aa5a --- /dev/null +++ b/libstdc++-v3/doc/html/manual/containers_and_c.html @@ -0,0 +1,90 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Interacting with C</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.76.1"/><meta name="keywords" content=" ISO C++ , library "/><link rel="home" href="../spine.html" title="The GNU C++ Library"/><link rel="up" href="containers.html" title="Chapter 9. Containers"/><link rel="prev" href="associative.html" title="Associative"/><link rel="next" href="iterators.html" title="Chapter 10. Iterators"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Interacting with C</th></tr><tr><td align="left"><a accesskey="p" href="associative.html">Prev</a> </td><th width="60%" align="center">Chapter 9. + Containers + +</th><td align="right"> <a accesskey="n" href="iterators.html">Next</a></td></tr></table><hr/></div><div class="section" title="Interacting with C"><div class="titlepage"><div><div><h2 class="title"><a id="std.containers.c"/>Interacting with C</h2></div></div></div><div class="section" title="Containers vs. Arrays"><div class="titlepage"><div><div><h3 class="title"><a id="containers.c.vs_array"/>Containers vs. Arrays</h3></div></div></div><p> + You're writing some code and can't decide whether to use builtin + arrays or some kind of container. There are compelling reasons + to use one of the container classes, but you're afraid that + you'll eventually run into difficulties, change everything back + to arrays, and then have to change all the code that uses those + data types to keep up with the change. + </p><p> + If your code makes use of the standard algorithms, this isn't as + scary as it sounds. The algorithms don't know, nor care, about + the kind of <span class="quote">“<span class="quote">container</span>”</span> on which they work, since + the algorithms are only given endpoints to work with. For the + container classes, these are iterators (usually + <code class="code">begin()</code> and <code class="code">end()</code>, but not always). + For builtin arrays, these are the address of the first element + and the <a class="link" href="iterators.html#iterators.predefined.end" title="One Past the End">past-the-end</a> element. + </p><p> + Some very simple wrapper functions can hide all of that from the + rest of the code. For example, a pair of functions called + <code class="code">beginof</code> can be written, one that takes an array, + another that takes a vector. The first returns a pointer to the + first element, and the second returns the vector's + <code class="code">begin()</code> iterator. + </p><p> + The functions should be made template functions, and should also + be declared inline. As pointed out in the comments in the code + below, this can lead to <code class="code">beginof</code> being optimized out + of existence, so you pay absolutely nothing in terms of increased + code size or execution time. + </p><p> + The result is that if all your algorithm calls look like + </p><pre class="programlisting"> + std::transform(beginof(foo), endof(foo), beginof(foo), SomeFunction); + </pre><p> + then the type of foo can change from an array of ints to a vector + of ints to a deque of ints and back again, without ever changing + any client code. + </p><pre class="programlisting"> +// beginof +template<typename T> + inline typename vector<T>::iterator + beginof(vector<T> &v) + { return v.begin(); } + +template<typename T, unsigned int sz> + inline T* + beginof(T (&array)[sz]) { return array; } + +// endof +template<typename T> + inline typename vector<T>::iterator + endof(vector<T> &v) + { return v.end(); } + +template<typename T, unsigned int sz> + inline T* + endof(T (&array)[sz]) { return array + sz; } + +// lengthof +template<typename T> + inline typename vector<T>::size_type + lengthof(vector<T> &v) + { return v.size(); } + +template<typename T, unsigned int sz> + inline unsigned int + lengthof(T (&)[sz]) { return sz; } +</pre><p> + Astute readers will notice two things at once: first, that the + container class is still a <code class="code">vector<T></code> instead + of a more general <code class="code">Container<T></code>. This would + mean that three functions for <code class="code">deque</code> would have to be + added, another three for <code class="code">list</code>, and so on. This is + due to problems with getting template resolution correct; I find + it easier just to give the extra three lines and avoid confusion. + </p><p> + Second, the line + </p><pre class="programlisting"> + inline unsigned int lengthof (T (&)[sz]) { return sz; } + </pre><p> + looks just weird! Hint: unused parameters can be left nameless. + </p></div></div><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td align="left"><a accesskey="p" href="associative.html">Prev</a> </td><td align="center"><a accesskey="u" href="containers.html">Up</a></td><td align="right"> <a accesskey="n" href="iterators.html">Next</a></td></tr><tr><td align="left" valign="top">Associative </td><td align="center"><a accesskey="h" href="../spine.html">Home</a></td><td align="right" valign="top"> Chapter 10. + Iterators + +</td></tr></table></div></body></html> |