You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
100 lines
4.4 KiB
HTML
100 lines
4.4 KiB
HTML
<html lang="en">
|
|
<head>
|
|
<title>Arrays and pointers implementation - Using the GNU Compiler Collection (GCC)</title>
|
|
<meta http-equiv="Content-Type" content="text/html">
|
|
<meta name="description" content="Using the GNU Compiler Collection (GCC)">
|
|
<meta name="generator" content="makeinfo 4.13">
|
|
<link title="Top" rel="start" href="index.html#Top">
|
|
<link rel="up" href="C-Implementation.html#C-Implementation" title="C Implementation">
|
|
<link rel="prev" href="Floating-point-implementation.html#Floating-point-implementation" title="Floating point implementation">
|
|
<link rel="next" href="Hints-implementation.html#Hints-implementation" title="Hints implementation">
|
|
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
|
|
<!--
|
|
Copyright (C) 1988-2015 Free Software Foundation, Inc.
|
|
|
|
Permission is granted to copy, distribute and/or modify this document
|
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
|
any later version published by the Free Software Foundation; with the
|
|
Invariant Sections being ``Funding Free Software'', the Front-Cover
|
|
Texts being (a) (see below), and with the Back-Cover Texts being (b)
|
|
(see below). A copy of the license is included in the section entitled
|
|
``GNU Free Documentation License''.
|
|
|
|
(a) The FSF's Front-Cover Text is:
|
|
|
|
A GNU Manual
|
|
|
|
(b) The FSF's Back-Cover Text is:
|
|
|
|
You have freedom to copy and modify this GNU Manual, like GNU
|
|
software. Copies published by the Free Software Foundation raise
|
|
funds for GNU development.-->
|
|
<meta http-equiv="Content-Style-Type" content="text/css">
|
|
<style type="text/css"><!--
|
|
pre.display { font-family:inherit }
|
|
pre.format { font-family:inherit }
|
|
pre.smalldisplay { font-family:inherit; font-size:smaller }
|
|
pre.smallformat { font-family:inherit; font-size:smaller }
|
|
pre.smallexample { font-size:smaller }
|
|
pre.smalllisp { font-size:smaller }
|
|
span.sc { font-variant:small-caps }
|
|
span.roman { font-family:serif; font-weight:normal; }
|
|
span.sansserif { font-family:sans-serif; font-weight:normal; }
|
|
--></style>
|
|
</head>
|
|
<body>
|
|
<div class="node">
|
|
<a name="Arrays-and-pointers-implementation"></a>
|
|
<p>
|
|
Next: <a rel="next" accesskey="n" href="Hints-implementation.html#Hints-implementation">Hints implementation</a>,
|
|
Previous: <a rel="previous" accesskey="p" href="Floating-point-implementation.html#Floating-point-implementation">Floating point implementation</a>,
|
|
Up: <a rel="up" accesskey="u" href="C-Implementation.html#C-Implementation">C Implementation</a>
|
|
<hr>
|
|
</div>
|
|
|
|
<h3 class="section">4.7 Arrays and Pointers</h3>
|
|
|
|
<ul>
|
|
<li><cite>The result of converting a pointer to an integer or
|
|
vice versa (C90 6.3.4, C99 and C11 6.3.2.3).</cite>
|
|
|
|
<p>A cast from pointer to integer discards most-significant bits if the
|
|
pointer representation is larger than the integer type,
|
|
sign-extends<a rel="footnote" href="#fn-1" name="fnd-1"><sup>1</sup></a>
|
|
if the pointer representation is smaller than the integer type, otherwise
|
|
the bits are unchanged.
|
|
<!-- ??? We've always claimed that pointers were unsigned entities. -->
|
|
<!-- Shouldn't we therefore be doing zero-extension? If so, the bug -->
|
|
<!-- is in convert_to_integer, where we call type_for_size and request -->
|
|
<!-- a signed integral type. On the other hand, it might be most useful -->
|
|
<!-- for the target if we extend according to POINTERS_EXTEND_UNSIGNED. -->
|
|
|
|
<p>A cast from integer to pointer discards most-significant bits if the
|
|
pointer representation is smaller than the integer type, extends according
|
|
to the signedness of the integer type if the pointer representation
|
|
is larger than the integer type, otherwise the bits are unchanged.
|
|
|
|
<p>When casting from pointer to integer and back again, the resulting
|
|
pointer must reference the same object as the original pointer, otherwise
|
|
the behavior is undefined. That is, one may not use integer arithmetic to
|
|
avoid the undefined behavior of pointer arithmetic as proscribed in
|
|
C99 and C11 6.5.6/8.
|
|
|
|
<li><cite>The size of the result of subtracting two pointers to elements
|
|
of the same array (C90 6.3.6, C99 and C11 6.5.6).</cite>
|
|
|
|
<p>The value is as specified in the standard and the type is determined
|
|
by the ABI.
|
|
|
|
</ul>
|
|
|
|
<div class="footnote">
|
|
<hr>
|
|
<h4>Footnotes</h4><p class="footnote"><small>[<a name="fn-1" href="#fnd-1">1</a>]</small> Future versions of GCC may zero-extend, or use
|
|
a target-defined <code>ptr_extend</code> pattern. Do not rely on sign extension.</p>
|
|
|
|
<hr></div>
|
|
|
|
</body></html>
|
|
|