diff options
Diffstat (limited to 'gcc-4.4.3/libstdc++-v3/doc/html/manual/bk01pt08ch19s02.html')
| -rw-r--r-- | gcc-4.4.3/libstdc++-v3/doc/html/manual/bk01pt08ch19s02.html | 86 |
1 files changed, 0 insertions, 86 deletions
diff --git a/gcc-4.4.3/libstdc++-v3/doc/html/manual/bk01pt08ch19s02.html b/gcc-4.4.3/libstdc++-v3/doc/html/manual/bk01pt08ch19s02.html deleted file mode 100644 index ba36e2fd5..000000000 --- a/gcc-4.4.3/libstdc++-v3/doc/html/manual/bk01pt08ch19s02.html +++ /dev/null @@ -1,86 +0,0 @@ -<?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>One Past the End</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="bk01pt08ch19.html" title="Chapter 19. Predefined" /><link rel="prev" href="bk01pt08ch19.html" title="Chapter 19. Predefined" /><link rel="next" href="algorithms.html" title="Part IX. Algorithms" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">One Past the End</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="bk01pt08ch19.html">Prev</a> </td><th width="60%" align="center">Chapter 19. Predefined</th><td width="20%" align="right"> <a accesskey="n" href="algorithms.html">Next</a></td></tr></table><hr /></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="iterators.predefined.end"></a>One Past the End</h2></div></div></div><p>This starts off sounding complicated, but is actually very easy, - especially towards the end. Trust me. - </p><p>Beginners usually have a little trouble understand the whole - 'past-the-end' thing, until they remember their early algebra classes - (see, they <span class="emphasis"><em>told</em></span> you that stuff would come in handy!) and - the concept of half-open ranges. - </p><p>First, some history, and a reminder of some of the funkier rules in - C and C++ for builtin arrays. The following rules have always been - true for both languages: - </p><div class="orderedlist"><ol type="1"><li><p>You can point anywhere in the array, <span class="emphasis"><em>or to the first element - past the end of the array</em></span>. A pointer that points to one - past the end of the array is guaranteed to be as unique as a - pointer to somewhere inside the array, so that you can compare - such pointers safely. - </p></li><li><p>You can only dereference a pointer that points into an array. - If your array pointer points outside the array -- even to just - one past the end -- and you dereference it, Bad Things happen. - </p></li><li><p>Strictly speaking, simply pointing anywhere else invokes - undefined behavior. Most programs won't puke until such a - pointer is actually dereferenced, but the standards leave that - up to the platform. - </p></li></ol></div><p>The reason this past-the-end addressing was allowed is to make it - easy to write a loop to go over an entire array, e.g., - while (*d++ = *s++);. - </p><p>So, when you think of two pointers delimiting an array, don't think - of them as indexing 0 through n-1. Think of them as <span class="emphasis"><em>boundary - markers</em></span>: - </p><pre class="programlisting"> - - beginning end - | | - | | This is bad. Always having to - | | remember to add or subtract one. - | | Off-by-one bugs very common here. - V V - array of N elements - |---|---|--...--|---|---| - | 0 | 1 | ... |N-2|N-1| - |---|---|--...--|---|---| - - ^ ^ - | | - | | This is good. This is safe. This - | | is guaranteed to work. Just don't - | | dereference 'end'. - beginning end - - </pre><p>See? Everything between the boundary markers is part of the array. - Simple. - </p><p>Now think back to your junior-high school algebra course, when you - were learning how to draw graphs. Remember that a graph terminating - with a solid dot meant, "Everything up through this point," - and a graph terminating with an open dot meant, "Everything up - to, but not including, this point," respectively called closed - and open ranges? Remember how closed ranges were written with - brackets, <span class="emphasis"><em>[a,b]</em></span>, and open ranges were written with parentheses, - <span class="emphasis"><em>(a,b)</em></span>? - </p><p>The boundary markers for arrays describe a <span class="emphasis"><em>half-open range</em></span>, - starting with (and including) the first element, and ending with (but - not including) the last element: <span class="emphasis"><em>[beginning,end)</em></span>. See, I - told you it would be simple in the end. - </p><p>Iterators, and everything working with iterators, follows this same - time-honored tradition. A container's <code class="code">begin()</code> method returns - an iterator referring to the first element, and its <code class="code">end()</code> - method returns a past-the-end iterator, which is guaranteed to be - unique and comparable against any other iterator pointing into the - middle of the container. - </p><p>Container constructors, container methods, and algorithms, all take - pairs of iterators describing a range of values on which to operate. - All of these ranges are half-open ranges, so you pass the beginning - iterator as the starting parameter, and the one-past-the-end iterator - as the finishing parameter. - </p><p>This generalizes very well. You can operate on sub-ranges quite - easily this way; functions accepting a <span class="emphasis"><em>[first,last)</em></span> range - don't know or care whether they are the boundaries of an entire {array, - sequence, container, whatever}, or whether they only enclose a few - elements from the center. This approach also makes zero-length - sequences very simple to recognize: if the two endpoints compare - equal, then the {array, sequence, container, whatever} is empty. - </p><p>Just don't dereference <code class="code">end()</code>. - </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="bk01pt08ch19.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="bk01pt08ch19.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="algorithms.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 19. Predefined </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> Part IX. - Algorithms - -</td></tr></table></div></body></html> |