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141 lines
7.4 KiB
HTML
141 lines
7.4 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2019 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Free Software" and "Free Software Needs
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Free Documentation", with the Front-Cover Texts being "A GNU Manual,"
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and with the Back-Cover Texts as in (a) below.
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(a) The FSF's Back-Cover Text is: "You are free to copy and modify
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this GNU Manual. Buying copies from GNU Press supports the FSF in
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developing GNU and promoting software freedom." -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>C Constants (Debugging with GDB)</title>
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<meta name="description" content="C Constants (Debugging with GDB)">
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<meta name="keywords" content="C Constants (Debugging with GDB)">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="C.html#C" rel="up" title="C">
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<link href="C-Plus-Plus-Expressions.html#C-Plus-Plus-Expressions" rel="next" title="C Plus Plus Expressions">
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<link href="C-Operators.html#C-Operators" rel="prev" title="C Operators">
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</head>
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<body lang="en">
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<a name="C-Constants"></a>
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<div class="header">
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<p>
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Next: <a href="C-Plus-Plus-Expressions.html#C-Plus-Plus-Expressions" accesskey="n" rel="next">C Plus Plus Expressions</a>, Previous: <a href="C-Operators.html#C-Operators" accesskey="p" rel="prev">C Operators</a>, Up: <a href="C.html#C" accesskey="u" rel="up">C</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="C-and-C_002b_002b-Constants"></a>
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<h4 class="subsubsection">15.4.1.2 C and C<tt>++</tt> Constants</h4>
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<a name="index-C-and-C_002b_002b-constants"></a>
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<p><small>GDB</small> allows you to express the constants of C and C<tt>++</tt> in the
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following ways:
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</p>
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<ul>
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<li> Integer constants are a sequence of digits. Octal constants are
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specified by a leading ‘<samp>0</samp>’ (i.e. zero), and hexadecimal constants
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by a leading ‘<samp>0x</samp>’ or ‘<samp>0X</samp>’. Constants may also end with a letter
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‘<samp>l</samp>’, specifying that the constant should be treated as a
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<code>long</code> value.
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</li><li> Floating point constants are a sequence of digits, followed by a decimal
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point, followed by a sequence of digits, and optionally followed by an
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exponent. An exponent is of the form:
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‘<samp>e<span class="roman">[[</span>+<span class="roman">]|</span><span class="nolinebreak">-</span><span class="roman">]</span><var>nnn</var><!-- /@w --></samp>’, where <var>nnn</var> is another
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sequence of digits. The ‘<samp>+</samp>’ is optional for positive exponents.
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A floating-point constant may also end with a letter ‘<samp>f</samp>’ or
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‘<samp>F</samp>’, specifying that the constant should be treated as being of
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the <code>float</code> (as opposed to the default <code>double</code>) type; or with
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a letter ‘<samp>l</samp>’ or ‘<samp>L</samp>’, which specifies a <code>long double</code>
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constant.
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</li><li> Enumerated constants consist of enumerated identifiers, or their
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integral equivalents.
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</li><li> Character constants are a single character surrounded by single quotes
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(<code>'</code>), or a number—the ordinal value of the corresponding character
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(usually its <small>ASCII</small> value). Within quotes, the single character may
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be represented by a letter or by <em>escape sequences</em>, which are of
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the form ‘<samp>\<var>nnn</var></samp>’, where <var>nnn</var> is the octal representation
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of the character’s ordinal value; or of the form ‘<samp>\<var>x</var></samp>’, where
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‘<samp><var>x</var></samp>’ is a predefined special character—for example,
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‘<samp>\n</samp>’ for newline.
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<p>Wide character constants can be written by prefixing a character
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constant with ‘<samp>L</samp>’, as in C. For example, ‘<samp>L'x'</samp>’ is the wide
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form of ‘<samp>x</samp>’. The target wide character set is used when
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computing the value of this constant (see <a href="Character-Sets.html#Character-Sets">Character Sets</a>).
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</p>
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</li><li> String constants are a sequence of character constants surrounded by
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double quotes (<code>"</code>). Any valid character constant (as described
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above) may appear. Double quotes within the string must be preceded by
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a backslash, so for instance ‘<samp>"a\"b'c"</samp>’ is a string of five
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characters.
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<p>Wide string constants can be written by prefixing a string constant
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with ‘<samp>L</samp>’, as in C. The target wide character set is used when
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computing the value of this constant (see <a href="Character-Sets.html#Character-Sets">Character Sets</a>).
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</p>
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</li><li> Pointer constants are an integral value. You can also write pointers
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to constants using the C operator ‘<samp>&</samp>’.
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</li><li> Array constants are comma-separated lists surrounded by braces ‘<samp>{</samp>’
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and ‘<samp>}</samp>’; for example, ‘<samp>{1,2,3}</samp>’ is a three-element array of
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integers, ‘<samp>{{1,2}, {3,4}, {5,6}}</samp>’ is a three-by-two array,
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and ‘<samp>{&"hi", &"there", &"fred"}</samp>’ is a three-element array of pointers.
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</li></ul>
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<hr>
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<div class="header">
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<p>
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Next: <a href="C-Plus-Plus-Expressions.html#C-Plus-Plus-Expressions" accesskey="n" rel="next">C Plus Plus Expressions</a>, Previous: <a href="C-Operators.html#C-Operators" accesskey="p" rel="prev">C Operators</a>, Up: <a href="C.html#C" accesskey="u" rel="up">C</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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