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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"><html><head><title>An Introduction To The SQLite C/C++ Interface</title><style type="text/css">body { margin: auto; font-family: "Verdana" "sans-serif"; padding: 8px 1%;}a { color: #45735f }a:visited { color: #734559 }.logo { position:absolute; margin:3px; }.tagline { float:right; text-align:right; font-style:italic; width:240px; margin:12px; margin-top:58px;}.toolbar { font-variant: small-caps; text-align: center; line-height: 1.6em; margin: 0; padding:1px 8px;}.toolbar a { color: white; text-decoration: none; padding: 6px 12px; }.toolbar a:visited { color: white; }.toolbar a:hover { color: #80a796; background: white; }.content { margin: 5%; }.content dt { font-weight:bold; }.content dd { margin-bottom: 25px; margin-left:20%; }.content ul { padding:0px; padding-left: 15px; margin:0px; }/* rounded corners */.se { background: url(images/se.png) 100% 100% no-repeat #80a796}.sw { background: url(images/sw.png) 0% 100% no-repeat }.ne { background: url(images/ne.png) 100% 0% no-repeat }.nw { background: url(images/nw.png) 0% 0% no-repeat }</style><meta http-equiv="content-type" content="text/html; charset=UTF-8"> </head><body><div><!-- container div to satisfy validator --><a href="index.html"><img class="logo" src="images/SQLite.gif" alt="SQLite Logo" border="0"></a><div><!-- IE hack to prevent disappearing logo--></div><div class="tagline">Small. Fast. Reliable.<br>Choose any three.</div><table width=100% style="clear:both"><tr><td> <div class="se"><div class="sw"><div class="ne"><div class="nw"> <div class="toolbar"> <a href="about.html">About</a> <a href="sitemap.html">Sitemap</a> <a href="docs.html">Documentation</a> <a href="download.html">Download</a> <a href="copyright.html">License</a> <a href="news.html">News</a> <a href="http://www.sqlite.org/cvstrac/index">Developers</a> <a href="support.html">Support</a> </div></div></div></div></div></td></tr></table> <h1> An Introduction To The SQLite C/C++ Interface</h1><p> This article provides an overview and roadmap to the C/C++ interface to SQLite.</p><p> Early versions of SQLite were very easy to learn since they only supported 5 C/C++ interfaces. But as SQLite has grown in capability new C/C++ interfaces have been added so that now there are over 150 distinct APIs. This can be overwhelming to a new programmer. Fortunately, most of the C/C++ interfaces in SQLite are very specialized and never need to be used. Despite having so many entry points, the core API is still relatively simple and easy to code to. This article aims to provide all of the background information needed to easily understand how SQLite works.</p><p> A separate document, <a href="c3ref/intro.html">The SQLite C/C++ Interface</a>, provides detailed specifications for all of the various C/C++ APIs for SQLite. Once the reader understands the basic principles of operation for SQLite, <a href="c3ref/intro.html">that document</a> should be used as a reference guide. This article is intended as introduction only and is neither a complete or authoritative reference for the SQLite API.</p><h2>1.0 Core Objects And Interfaces</h2><p> The principal function of an SQL database engine is to evaluate statements of SQL. In order to accomplish this purpose, the developer needs to know about two objects:</p><p><ul> <li> The <a href="c3ref/sqlite3.html">database connection</a> object: sqlite3 </li> <li> The <a href="c3ref/stmt.html">prepared statement</a> object: sqlite3_stmt </li></ul></p><p> Strictly speaking, the <a href="c3ref/stmt.html">prepared statement</a> object is not required since the convenience wrapper interfaces, <a href="c3ref/exec.html">sqlite3_exec</a> or <a href="c3ref/free_table.html">sqlite3_get_table</a>, that encapsulate and hide the <a href="c3ref/stmt.html">prepared statement</a> can be used instead. Nevertheless, and understanding of <a href="c3ref/stmt.html">prepared statements</a> is needed to make full use of SQLite.</p><p> The <a href="c3ref/sqlite3.html">database connection</a> and <a href="c3ref/stmt.html">prepared statement</a> objects are controlled by a small set of C/C++ interface routine listed below.</p><p><ul> <li> <a href="c3ref/open.html">sqlite3_open()</a> </li> <li> <a href="c3ref/prepare.html">sqlite3_prepare()</a> </li> <li> <a href="c3ref/step.html">sqlite3_step()</a> </li> <li> <a href="c3ref/column_blob.html">sqlite3_column()</a> </li> <li> <a href="c3ref/finalize.html">sqlite3_finalize()</a> </li> <li> <a href="c3ref/close.html">sqlite3_close()</a> </li></ul></p><p> The six C/C++ interface routines and two objects listed above form the core functionality of SQLite. The developer who understands them will have a good foundation for using SQLite.</p><p> Note that the list of routines is conceptual rather than actual. Many of these routines come in multiple versions. For example, the list above shows a single routine named <a href="c3ref/open.html">sqlite3_open()</a> when in fact there are three separate routines that accomplish the same thing in slightly different ways: <a href="c3ref/open.html">sqlite3_open()</a>, <a href="c3ref/open.html">sqlite3_open16()</a> and <a href="c3ref/open.html">sqlite3_open_v2()</a>. The list mentions <a href="c3ref/column_blob.html">sqlite3_column()</a> when in fact no such routine exists. The "sqlite3_column()" shown in the list is place holders for an entire families of routines to be used for extracting column data in various datatypes.</p><p> Here is a summary of what the core interfaces do:</p><table border="0" cellspacing="15"><tr><td valign="top" align="right"><a href="c3ref/open.html">sqlite3_open()</a></td><td valign="top"> This routine opens a connection to an SQLite database file and returns a <a href="c3ref/sqlite3.html">database connection</a> object. This is often the first SQLite API call that an application makes and is a prerequisite for most other SQLite APIs. Many SQLite interfaces require a pointer to the <a href="c3ref/sqlite3.html">database connection</a> object as their first parameter and can be thought of as methods on the <a href="c3ref/sqlite3.html">database connection</a> object. This routine is the constructor for the <a href="c3ref/sqlite3.html">database connection</a> object.</td><tr><td valign="top" align="right"><a href="c3ref/prepare.html">sqlite3_prepare()</a></td><td valign="top"> This routine converts SQL text into a <a href="c3ref/stmt.html">prepared statement</a> object and return a pointer to that object. This interface requires a <a href="c3ref/sqlite3.html">database connection</a> pointer created by a prior call to <a href="c3ref/open.html">sqlite3_open()</a> and a text string containing the SQL statement to be prepared. This API does not actually evaluate the SQL statement. It merely prepares the SQL statement for evaluation. <p>Note that the use of <a href="c3ref/prepare.html">sqlite3_prepare()</a> is not recommended for new applications. The alternative routine <a href="c3ref/prepare.html">sqlite3_prepare_v2()</a> should be used instead.</p></td><tr><td valign="top" align="right"><a href="c3ref/step.html">sqlite3_step()</a></td><td valign="top"> This routine is used to evaluate a <a href="c3ref/stmt.html">prepared statement</a> that has been previously created by the <a href="c3ref/prepare.html">sqlite3_prepare()</a> interface. The statement is evaluated up to the point where the first row of results are available. To advance to the second row of results, invoke <a href="c3ref/step.html">sqlite3_step()</a> again. Continue invoking <a href="c3ref/step.html">sqlite3_step()</a> until the statement is complete. Statements that do not return results (ex: INSERT, UPDATE, or DELETE statements) run to completion on a single call to <a href="c3ref/step.html">sqlite3_step()</a>.</td><tr><td valign="top" align="right"><a href="c3ref/column_blob.html">sqlite3_column()</a></td><td valign="top"> This routine returns a single column from the current row of a result set for a <a href="c3ref/stmt.html">prepared statement</a> that is being evaluated by <a href="c3ref/step.html">sqlite3_step()</a>. Each time <a href="c3ref/step.html">sqlite3_step()</a> stops with a new result set row, this routine can be called multiple times to find the values of all columns in that row. As noted above, there really is no such thing as a "sqlite3_column()" function in the SQLite API. Instead, what we here call "sqlite3_column()" is really a place-holder for an entire family of functions that return a value from the result set in various data types. There are also routines in this family that return the size of the result (if it is a string or BLOB) and the number of columns in the result set. <p><ul> <li> <a href="c3ref/column_blob.html">sqlite3_column_blob()</a> </li> <li> <a href="c3ref/column_blob.html">sqlite3_column_bytes()</a> </li> <li> <a href="c3ref/column_blob.html">sqlite3_column_bytes16()</a> </li>⌨️ 快捷键说明
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