73 lines
4.9 KiB
HTML
73 lines
4.9 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="security" content="public" />
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<meta name="Robots" content="index,follow" />
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<meta http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' />
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Literal strings in native methods" />
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<meta name="abstract" content="It is easier to encode literal strings in UTF-8 if the string is composed of characters with a 7-bit American Standard Code for Information Interchange (ASCII) representation." />
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<meta name="description" content="It is easier to encode literal strings in UTF-8 if the string is composed of characters with a 7-bit American Standard Code for Information Interchange (ASCII) representation." />
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<meta name="DC.Relation" scheme="URI" content="strings.htm" />
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<meta name="DC.Relation" scheme="URI" content="dynamic.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="literal" />
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<meta name="DC.Language" content="en-us" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Literal strings in native methods</title>
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</head>
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<body id="literal"><a name="literal"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Literal strings in native methods</h1>
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<div><p>It is easier to encode literal strings in UTF-8 if the string is
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composed of characters with a 7-bit American Standard Code for Information
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Interchange (ASCII) representation.</p>
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<p>If the string can be represented in ASCII, as most are, then the string
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can be bracketed by 'pragma' statements that change the current codepage of
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the compiler. Then, the compiler stores the string internally in the UTF-8
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form that is required by the JNI. If the string cannot be represented in ASCII,
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it is easier to treat the original extended binary-coded decimal interchange
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code (EBCDIC) string as a dynamic string, and process it using iconv() before
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passing it to the JNI. For more information on dynamic strings, see <a href="dynamic.htm">dynamic strings</a>.</p>
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<p>For example, to find the class named <samp class="codeph">java/lang/String</samp>,
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the code looks like this:</p>
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<pre> #pragma convert(819)
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myClass = (*env)->FindClass(env,"java/lang/String");
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#pragma convert(0)</pre>
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<p>The first pragma, with the number 819, informs the compiler to store all
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subsequent double-quoted strings (literal strings) in ASCII. The second pragma,
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with the number 0, tells the compiler to revert to the default code page of
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the compiler for double-quoted strings, which is usually the EBCDIC code page
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37. So, by bracketing this call with these pragmas, we satisfy the JNI requirement
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that string parameters are encoded in UTF-8.</p>
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<p><strong>Caution:</strong> Be careful with text substitutions. For example, if your
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code looks like this:</p>
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<pre> #pragma convert(819)
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#define MyString "java/lang/String"
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#pragma convert(0)
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myClass = (*env)->FindClass(env,MyString);</pre>
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<p>Then, the resulting string is EBCDIC, because the value of MyString is
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substituted into the FindClass call during compilation. At the time of this
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substitution, the pragma, number 819, is not in effect. Thus, literal strings
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are not stored in ASCII. </p>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="strings.htm" title="Many Java Native Interface (JNI) functions accept C language-style strings as parameters. For example, the FindClass() JNI function accepts a string parameter that specifies the fully-qualified name of a classfile. If the classfile is found, it is loaded by FindClass, and a reference to it is returned to the caller of FindClass.">Strings in native methods</a></div>
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</div>
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<div class="reltasks"><strong>Related tasks</strong><br />
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<div><a href="dynamic.htm" title="To manipulate string variables that are computed at run time, it may be necessary to convert strings to and from extended binary-coded decimal interchange (EBCDIC), Unicode, and UTF-8.">Convert dynamic strings to and from EBCDIC, Unicode, and UTF-8</a></div>
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</div>
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</div>
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</body>
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</html>
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