visus
/
toolchain-gcc-arm-embedded
Vērot 1
Pievienot zvaigznīti 0
Atdalīts 0
Kods Problēmas 0 Izmaiņu pieprasījumi 0 Laidieni 0 Vikivietne Aktivitāte
Nevar pievienot vairāk kā 25 tēmas Tēmai ir jāsākas ar burtu vai ciparu, tā var saturēt domu zīmes ('-') un var būt līdz 35 simboliem gara.
2 Revīzijas
1 Atzars
Koks: 898a39b5ab
Atzari Tagi
${ item.name }
Izveidot atzaru ${ searchTerm }
no '898a39b5ab'
${ noResults }
toolchain-gcc-arm-embedded/share/doc/gcc-arm-none-eabi/html/gcc/Qualifiers-implementation.html

131 rinda
6.2KB
Neapstrādāts Vainot Vēsture 

  1. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

  2. <html>

  3. <!-- Copyright (C) 1988-2020 Free Software Foundation, Inc.

  4. 

  5. Permission is granted to copy, distribute and/or modify this document

  6. under the terms of the GNU Free Documentation License, Version 1.3 or

  7. any later version published by the Free Software Foundation; with the

  8. Invariant Sections being "Funding Free Software", the Front-Cover

  9. Texts being (a) (see below), and with the Back-Cover Texts being (b)

  10. (see below).  A copy of the license is included in the section entitled

  11. "GNU Free Documentation License".

  12. 

  13. (a) The FSF's Front-Cover Text is:

  14. 

  15. A GNU Manual

  16. 

  17. (b) The FSF's Back-Cover Text is:

  18. 

  19. You have freedom to copy and modify this GNU Manual, like GNU

  20.      software.  Copies published by the Free Software Foundation raise

  21.      funds for GNU development. -->

  22. <!-- Created by GNU Texinfo 6.5, http://www.gnu.org/software/texinfo/ -->

  23. <head>

  24. <meta http-equiv="Content-Type" content="text/html; charset=utf-8">

  25. <title>Qualifiers implementation (Using the GNU Compiler Collection (GCC))</title>

  26. 

  27. <meta name="description" content="Qualifiers implementation (Using the GNU Compiler Collection (GCC))">

  28. <meta name="keywords" content="Qualifiers implementation (Using the GNU Compiler Collection (GCC))">

  29. <meta name="resource-type" content="document">

  30. <meta name="distribution" content="global">

  31. <meta name="Generator" content="makeinfo">

  32. <link href="index.html#Top" rel="start" title="Top">

  33. <link href="Option-Index.html#Option-Index" rel="index" title="Option Index">

  34. <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">

  35. <link href="C-Implementation.html#C-Implementation" rel="up" title="C Implementation">

  36. <link href="Declarators-implementation.html#Declarators-implementation" rel="next" title="Declarators implementation">

  37. <link href="Structures-unions-enumerations-and-bit_002dfields-implementation.html#Structures-unions-enumerations-and-bit_002dfields-implementation" rel="prev" title="Structures unions enumerations and bit-fields implementation">

  38. <style type="text/css">

  39. <!--

  40. a.summary-letter {text-decoration: none}

  41. blockquote.indentedblock {margin-right: 0em}

  42. blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}

  43. blockquote.smallquotation {font-size: smaller}

  44. div.display {margin-left: 3.2em}

  45. div.example {margin-left: 3.2em}

  46. div.lisp {margin-left: 3.2em}

  47. div.smalldisplay {margin-left: 3.2em}

  48. div.smallexample {margin-left: 3.2em}

  49. div.smalllisp {margin-left: 3.2em}

  50. kbd {font-style: oblique}

  51. pre.display {font-family: inherit}

  52. pre.format {font-family: inherit}

  53. pre.menu-comment {font-family: serif}

  54. pre.menu-preformatted {font-family: serif}

  55. pre.smalldisplay {font-family: inherit; font-size: smaller}

  56. pre.smallexample {font-size: smaller}

  57. pre.smallformat {font-family: inherit; font-size: smaller}

  58. pre.smalllisp {font-size: smaller}

  59. span.nolinebreak {white-space: nowrap}

  60. span.roman {font-family: initial; font-weight: normal}

  61. span.sansserif {font-family: sans-serif; font-weight: normal}

  62. ul.no-bullet {list-style: none}

  63. -->

  64. </style>

  65. 

  66. 

  67. </head>

  68. 

  69. <body lang="en">

  70. <a name="Qualifiers-implementation"></a>

  71. <div class="header">

  72. <p>

  73. Next: <a href="Declarators-implementation.html#Declarators-implementation" accesskey="n" rel="next">Declarators implementation</a>, Previous: <a href="Structures-unions-enumerations-and-bit_002dfields-implementation.html#Structures-unions-enumerations-and-bit_002dfields-implementation" accesskey="p" rel="prev">Structures unions enumerations and bit-fields implementation</a>, Up: <a href="C-Implementation.html#C-Implementation" accesskey="u" rel="up">C Implementation</a> &nbsp; [<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>

  74. </div>

  75. <hr>

  76. <a name="Qualifiers"></a>

  77. <h3 class="section">4.10 Qualifiers</h3>

  78. 

  79. <ul>

  80. <li> <cite>What constitutes an access to an object that has volatile-qualified

  81. type (C90 6.5.3, C99 and C11 6.7.3).</cite>

  82. 

  83. <p>Such an object is normally accessed by pointers and used for accessing

  84. hardware.  In most expressions, it is intuitively obvious what is a read

  85. and what is a write.  For example

  86. </p>

  87. <div class="smallexample">

  88. <pre class="smallexample">volatile int *dst = <var>somevalue</var>;

  89. volatile int *src = <var>someothervalue</var>;

  90. *dst = *src;

  91. </pre></div>

  92. 

  93. <p>will cause a read of the volatile object pointed to by <var>src</var> and store the

  94. value into the volatile object pointed to by <var>dst</var>.  There is no

  95. guarantee that these reads and writes are atomic, especially for objects

  96. larger than <code>int</code>.

  97. </p>

  98. <p>However, if the volatile storage is not being modified, and the value of

  99. the volatile storage is not used, then the situation is less obvious.

  100. For example

  101. </p>

  102. <div class="smallexample">

  103. <pre class="smallexample">volatile int *src = <var>somevalue</var>;

  104. *src;

  105. </pre></div>

  106. 

  107. <p>According to the C standard, such an expression is an rvalue whose type

  108. is the unqualified version of its original type, i.e. <code>int</code>.  Whether

  109. GCC interprets this as a read of the volatile object being pointed to or

  110. only as a request to evaluate the expression for its side effects depends

  111. on this type.

  112. </p>

  113. <p>If it is a scalar type, or on most targets an aggregate type whose only

  114. member object is of a scalar type, or a union type whose member objects

  115. are of scalar types, the expression is interpreted by GCC as a read of

  116. the volatile object; in the other cases, the expression is only evaluated

  117. for its side effects.

  118. </p>

  119. </li></ul>

  120. 

  121. <hr>

  122. <div class="header">

  123. <p>

  124. Next: <a href="Declarators-implementation.html#Declarators-implementation" accesskey="n" rel="next">Declarators implementation</a>, Previous: <a href="Structures-unions-enumerations-and-bit_002dfields-implementation.html#Structures-unions-enumerations-and-bit_002dfields-implementation" accesskey="p" rel="prev">Structures unions enumerations and bit-fields implementation</a>, Up: <a href="C-Implementation.html#C-Implementation" accesskey="u" rel="up">C Implementation</a> &nbsp; [<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>

  125. </div>

  126. 

  127. 

  128. 

  129. </body>

  130. </html>