113 lines
6.9 KiB
HTML
113 lines
6.9 KiB
HTML
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<title>Strings - Using as</title>
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<!--
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This file documents the GNU Assembler "as".
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Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002,
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2006, 2007 Free Software Foundation, Inc.
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<a name="Strings"></a>Next: <a rel="next" accesskey="n" href="Chars.html#Chars">Chars</a>,
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Up: <a rel="up" accesskey="u" href="Characters.html#Characters">Characters</a>
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<hr><br>
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</div>
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<h5 class="subsubsection">3.6.1.1 Strings</h5>
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<p><a name="index-string-constants-142"></a><a name="index-constants_002c-string-143"></a>A <dfn>string</dfn> is written between double-quotes. It may contain
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double-quotes or null characters. The way to get special characters
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into a string is to <dfn>escape</dfn> these characters: precede them with
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a backslash <span class="samp">\</span> character. For example <span class="samp">\\</span> represents
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one backslash: the first <code>\</code> is an escape which tells
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<span class="command">as</span> to interpret the second character literally as a backslash
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(which prevents <span class="command">as</span> from recognizing the second <code>\</code> as an
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escape character). The complete list of escapes follows.
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<p><a name="index-escape-codes_002c-character-144"></a><a name="index-character-escape-codes-145"></a>
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<dl>
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<!-- @item \a -->
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<!-- Mnemonic for ACKnowledge; for ASCII this is octal code 007. -->
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<a name="index-_0040code_007b_005cb_007d-_0028backspace-character_0029-146"></a><a name="index-backspace-_0028_0040code_007b_005cb_007d_0029-147"></a><dt><kbd>\b</kbd><dd>Mnemonic for backspace; for ASCII this is octal code 010.
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<!-- @item \e -->
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<!-- Mnemonic for EOText; for ASCII this is octal code 004. -->
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<p><a name="index-_0040code_007b_005cf_007d-_0028formfeed-character_0029-148"></a><a name="index-formfeed-_0028_0040code_007b_005cf_007d_0029-149"></a><br><dt><kbd>\f</kbd><dd>Mnemonic for FormFeed; for ASCII this is octal code 014.
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<p><a name="index-_0040code_007b_005cn_007d-_0028newline-character_0029-150"></a><a name="index-newline-_0028_0040code_007b_005cn_007d_0029-151"></a><br><dt><kbd>\n</kbd><dd>Mnemonic for newline; for ASCII this is octal code 012.
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<!-- @item \p -->
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<!-- Mnemonic for prefix; for ASCII this is octal code 033, usually known as @code{escape}. -->
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<p><a name="index-_0040code_007b_005cr_007d-_0028carriage-return-character_0029-152"></a><a name="index-carriage-return-_0028_0040code_007b_005cr_007d_0029-153"></a><br><dt><kbd>\r</kbd><dd>Mnemonic for carriage-Return; for ASCII this is octal code 015.
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<!-- @item \s -->
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<!-- Mnemonic for space; for ASCII this is octal code 040. Included for compliance with -->
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<!-- other assemblers. -->
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<p><a name="index-_0040code_007b_005ct_007d-_0028tab_0029-154"></a><a name="index-tab-_0028_0040code_007b_005ct_007d_0029-155"></a><br><dt><kbd>\t</kbd><dd>Mnemonic for horizontal Tab; for ASCII this is octal code 011.
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<!-- @item \v -->
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<!-- Mnemonic for Vertical tab; for ASCII this is octal code 013. -->
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<!-- @item \x @var{digit} @var{digit} @var{digit} -->
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<!-- A hexadecimal character code. The numeric code is 3 hexadecimal digits. -->
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<p><a name="index-_0040code_007b_005c_0040var_007bddd_007d_007d-_0028octal-character-code_0029-156"></a><a name="index-octal-character-code-_0028_0040code_007b_005c_0040var_007bddd_007d_007d_0029-157"></a><br><dt><kbd>\ </kbd><var>digit</var> <var>digit</var> <var>digit</var><dd>An octal character code. The numeric code is 3 octal digits.
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For compatibility with other Unix systems, 8 and 9 are accepted as digits:
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for example, <code>\008</code> has the value 010, and <code>\009</code> the value 011.
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<p><a name="index-_0040code_007b_005c_0040var_007bxd_002e_002e_002e_007d_007d-_0028hex-character-code_0029-158"></a><a name="index-hex-character-code-_0028_0040code_007b_005c_0040var_007bxd_002e_002e_002e_007d_007d_0029-159"></a><br><dt><kbd>\</kbd><code>x</code> <var>hex-digits...</var><dd>A hex character code. All trailing hex digits are combined. Either upper or
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lower case <code>x</code> works.
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<p><a name="index-_0040code_007b_005c_005c_007d-_0028_0040samp_007b_005c_007d-character_0029-160"></a><a name="index-backslash-_0028_0040code_007b_005c_005c_007d_0029-161"></a><br><dt><kbd>\\</kbd><dd>Represents one <span class="samp">\</span> character.
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<!-- @item \' -->
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<!-- Represents one @samp{'} (accent acute) character. -->
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<!-- This is needed in single character literals -->
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<!-- (@xref{Characters,,Character Constants}.) to represent -->
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<!-- a @samp{'}. -->
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<p><a name="index-_0040code_007b_005c_0022_007d-_0028doublequote-character_0029-162"></a><a name="index-doublequote-_0028_0040code_007b_005c_0022_007d_0029-163"></a><br><dt><kbd>\"</kbd><dd>Represents one <span class="samp">"</span> character. Needed in strings to represent
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this character, because an unescaped <span class="samp">"</span> would end the string.
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<br><dt><kbd>\ </kbd><var>anything-else</var><dd>Any other character when escaped by <kbd>\</kbd> gives a warning, but
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assembles as if the <span class="samp">\</span> was not present. The idea is that if
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you used an escape sequence you clearly didn't want the literal
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interpretation of the following character. However <span class="command">as</span> has no
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other interpretation, so <span class="command">as</span> knows it is giving you the wrong
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code and warns you of the fact.
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</dl>
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<p>Which characters are escapable, and what those escapes represent,
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varies widely among assemblers. The current set is what we think
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the BSD 4.2 assembler recognizes, and is a subset of what most C
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compilers recognize. If you are in doubt, do not use an escape
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sequence.
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</body></html>
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