| <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> |
| <html> |
| <!-- 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. --> |
| <!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ --> |
| <head> |
| <title>Using the GNU Compiler Collection (GCC): Structures unions enumerations and bit-fields implementation</title> |
| |
| <meta name="description" content="Using the GNU Compiler Collection (GCC): Structures unions enumerations and bit-fields implementation"> |
| <meta name="keywords" content="Using the GNU Compiler Collection (GCC): Structures unions enumerations and bit-fields implementation"> |
| <meta name="resource-type" content="document"> |
| <meta name="distribution" content="global"> |
| <meta name="Generator" content="makeinfo"> |
| <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> |
| <link href="index.html#Top" rel="start" title="Top"> |
| <link href="Option-Index.html#Option-Index" rel="index" title="Option Index"> |
| <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> |
| <link href="C-Implementation.html#C-Implementation" rel="up" title="C Implementation"> |
| <link href="Qualifiers-implementation.html#Qualifiers-implementation" rel="next" title="Qualifiers implementation"> |
| <link href="Hints-implementation.html#Hints-implementation" rel="prev" title="Hints implementation"> |
| <style type="text/css"> |
| <!-- |
| a.summary-letter {text-decoration: none} |
| blockquote.smallquotation {font-size: smaller} |
| div.display {margin-left: 3.2em} |
| div.example {margin-left: 3.2em} |
| div.indentedblock {margin-left: 3.2em} |
| div.lisp {margin-left: 3.2em} |
| div.smalldisplay {margin-left: 3.2em} |
| div.smallexample {margin-left: 3.2em} |
| div.smallindentedblock {margin-left: 3.2em; font-size: smaller} |
| div.smalllisp {margin-left: 3.2em} |
| kbd {font-style:oblique} |
| pre.display {font-family: inherit} |
| pre.format {font-family: inherit} |
| pre.menu-comment {font-family: serif} |
| pre.menu-preformatted {font-family: serif} |
| pre.smalldisplay {font-family: inherit; font-size: smaller} |
| pre.smallexample {font-size: smaller} |
| pre.smallformat {font-family: inherit; font-size: smaller} |
| pre.smalllisp {font-size: smaller} |
| span.nocodebreak {white-space:nowrap} |
| span.nolinebreak {white-space:nowrap} |
| span.roman {font-family:serif; font-weight:normal} |
| span.sansserif {font-family:sans-serif; font-weight:normal} |
| ul.no-bullet {list-style: none} |
| --> |
| </style> |
| |
| |
| </head> |
| |
| <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> |
| <a name="Structures-unions-enumerations-and-bit_002dfields-implementation"></a> |
| <div class="header"> |
| <p> |
| Next: <a href="Qualifiers-implementation.html#Qualifiers-implementation" accesskey="n" rel="next">Qualifiers implementation</a>, Previous: <a href="Hints-implementation.html#Hints-implementation" accesskey="p" rel="prev">Hints implementation</a>, Up: <a href="C-Implementation.html#C-Implementation" accesskey="u" rel="up">C Implementation</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> |
| </div> |
| <hr> |
| <a name="Structures_002c-unions_002c-enumerations_002c-and-bit_002dfields"></a> |
| <h3 class="section">4.9 Structures, unions, enumerations, and bit-fields</h3> |
| |
| <ul> |
| <li> <cite>A member of a union object is accessed using a member of a |
| different type (C90 6.3.2.3).</cite> |
| |
| <p>The relevant bytes of the representation of the object are treated as |
| an object of the type used for the access. See <a href="Optimize-Options.html#Type_002dpunning">Type-punning</a>. This |
| may be a trap representation. |
| </p> |
| </li><li> <cite>Whether a “plain” <code>int</code> bit-field is treated as a |
| <code>signed int</code> bit-field or as an <code>unsigned int</code> bit-field |
| (C90 6.5.2, C90 6.5.2.1, C99 and C11 6.7.2, C99 and C11 6.7.2.1).</cite> |
| |
| <a name="index-funsigned_002dbitfields-1"></a> |
| <p>By default it is treated as <code>signed int</code> but this may be changed |
| by the <samp>-funsigned-bitfields</samp> option. |
| </p> |
| </li><li> <cite>Allowable bit-field types other than <code>_Bool</code>, <code>signed int</code>, |
| and <code>unsigned int</code> (C99 and C11 6.7.2.1).</cite> |
| |
| <p>Other integer types, such as <code>long int</code>, and enumerated types are |
| permitted even in strictly conforming mode. |
| </p> |
| </li><li> <cite>Whether atomic types are permitted for bit-fields (C11 6.7.2.1).</cite> |
| |
| <p>Atomic types are not permitted for bit-fields. |
| </p> |
| </li><li> <cite>Whether a bit-field can straddle a storage-unit boundary (C90 |
| 6.5.2.1, C99 and C11 6.7.2.1).</cite> |
| |
| <p>Determined by ABI. |
| </p> |
| </li><li> <cite>The order of allocation of bit-fields within a unit (C90 |
| 6.5.2.1, C99 and C11 6.7.2.1).</cite> |
| |
| <p>Determined by ABI. |
| </p> |
| </li><li> <cite>The alignment of non-bit-field members of structures (C90 |
| 6.5.2.1, C99 and C11 6.7.2.1).</cite> |
| |
| <p>Determined by ABI. |
| </p> |
| </li><li> <cite>The integer type compatible with each enumerated type (C90 |
| 6.5.2.2, C99 and C11 6.7.2.2).</cite> |
| |
| <a name="index-fshort_002denums-1"></a> |
| <p>Normally, the type is <code>unsigned int</code> if there are no negative |
| values in the enumeration, otherwise <code>int</code>. If |
| <samp>-fshort-enums</samp> is specified, then if there are negative values |
| it is the first of <code>signed char</code>, <code>short</code> and <code>int</code> |
| that can represent all the values, otherwise it is the first of |
| <code>unsigned char</code>, <code>unsigned short</code> and <code>unsigned int</code> |
| that can represent all the values. |
| </p> |
| <p>On some targets, <samp>-fshort-enums</samp> is the default; this is |
| determined by the ABI. |
| </p> |
| </li></ul> |
| |
| <hr> |
| <div class="header"> |
| <p> |
| Next: <a href="Qualifiers-implementation.html#Qualifiers-implementation" accesskey="n" rel="next">Qualifiers implementation</a>, Previous: <a href="Hints-implementation.html#Hints-implementation" accesskey="p" rel="prev">Hints implementation</a>, Up: <a href="C-Implementation.html#C-Implementation" accesskey="u" rel="up">C Implementation</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> |
| </div> |
| |
| |
| |
| </body> |
| </html> |
