1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml"> 4 <head> 5 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 6 <title>Replacing Records Using Cursors</title> 7 <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> 8 <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> 9 <link rel="start" href="index.html" title="Getting Started with Berkeley DB" /> 10 <link rel="up" href="Cursors.html" title="Chapter��4.��Using Cursors" /> 11 <link rel="prev" href="DeleteEntryWCursor.html" title="Deleting Records Using Cursors" /> 12 <link rel="next" href="CoreCursorUsage.html" title="Cursor Example" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">Replacing Records Using Cursors</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="DeleteEntryWCursor.html">Prev</a>��</td> 22 <th width="60%" align="center">Chapter��4.��Using Cursors</th> 23 <td width="20%" align="right">��<a accesskey="n" href="CoreCursorUsage.html">Next</a></td> 24 </tr> 25 </table> 26 <hr /> 27 </div> 28 <div class="sect1" lang="en" xml:lang="en"> 29 <div class="titlepage"> 30 <div> 31 <div> 32 <h2 class="title" style="clear: both"><a id="ReplacingEntryWCursor"></a>Replacing Records Using Cursors</h2> 33 </div> 34 </div> 35 </div> 36 <p> 37 You replace the data for a database record by using 38 39 40 41 42 <span> 43 44 <code class="methodname">Dbc::put()</code> 45 with the <code class="literal">DB_CURRENT</code> flag. 46 </span> 47 48 </p> 49 <a id="cxx_cursor9"></a> 50 <pre class="programlisting">#include <db_cxx.h> 51#include <string.h> 52 53... 54 55Db my_database(NULL, 0); 56Dbc *cursorp; 57 58int ret; 59char *key1str = "My first string"; 60char *replacement_data = "replace me"; 61 62try { 63 // Database open omitted 64 65 // Get the cursor 66 my_database.cursor(NULL, &cursorp, 0); 67 68 // Set up our DBTs 69 Dbt key(key1str, strlen(key1str) + 1); 70 Dbt data; 71 72 // Position the cursor */ 73 ret = cursorp->get(&key, &data, DB_SET); 74 if (ret == 0) { 75 data.set_data(replacement_data); 76 data.set_size(strlen(replacement_data) + 1); 77 cursorp->put(&key, &data, DB_CURRENT); 78 } 79} catch(DbException &e) { 80 my_database.err(e.get_errno(), "Error!"); 81} catch(std::exception &e) { 82 my_database.errx("Error! %s", e.what()); 83} 84 85// Cursors must be closed 86if (cursorp != NULL) 87 cursorp->close(); 88 89my_database.close(0);</pre> 90 <p> 91 Note that you cannot change a record's key using this method; the key 92 parameter is always ignored when you replace a record. 93 </p> 94 <p> 95 When replacing the data portion of a record, if you are replacing a 96 record that is a member of a sorted duplicates set, then the replacement 97 will be successful only if the new record sorts identically to the old 98 record. This means that if you are replacing a record that is a member 99 of a sorted duplicates set, and if you are using the default 100 lexicographic sort, then the replacement will fail due to violating the 101 sort order. However, if you 102 provide a custom sort routine that, for example, sorts based on just a 103 few bytes out of the data item, then potentially you can perform 104 a direct replacement and still not violate the restrictions described 105 here. 106 </p> 107 <p> 108 <span>Under these circumstances, if</span> 109 110 you want to replace the data contained by a duplicate record, 111 <span> 112 and you are not using a custom sort routine, then 113 </span> 114 delete the record and create a new record with the desired key and data. 115 </p> 116 </div> 117 <div class="navfooter"> 118 <hr /> 119 <table width="100%" summary="Navigation footer"> 120 <tr> 121 <td width="40%" align="left"><a accesskey="p" href="DeleteEntryWCursor.html">Prev</a>��</td> 122 <td width="20%" align="center"> 123 <a accesskey="u" href="Cursors.html">Up</a> 124 </td> 125 <td width="40%" align="right">��<a accesskey="n" href="CoreCursorUsage.html">Next</a></td> 126 </tr> 127 <tr> 128 <td width="40%" align="left" valign="top">Deleting Records Using Cursors��</td> 129 <td width="20%" align="center"> 130 <a accesskey="h" href="index.html">Home</a> 131 </td> 132 <td width="40%" align="right" valign="top">��Cursor Example</td> 133 </tr> 134 </table> 135 </div> 136 </body> 137</html> 138