2000-05-29 22:20:15 +04:00
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#
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# Run this Tcl script to generate the sqlite.html file.
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#
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2000-06-06 22:24:42 +04:00
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set rcsid {$Id: c_interface.tcl,v 1.4 2000/06/06 18:24:42 drh Exp $}
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2000-05-29 22:20:15 +04:00
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puts {<html>
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<head>
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<title>The C language interface to the SQLite library</title>
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</head>
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<body bgcolor=white>
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<h1 align=center>
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The C language interface to the SQLite library
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</h1>}
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puts "<p align=center>
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(This page was last modified on [lrange $rcsid 3 4] GMT)
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</p>"
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puts {
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<p>The SQLite library is designed to be very easy to use from
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a C or C++ program. This document gives an overview of the C/C++
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programming interface.</p>
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2000-05-29 22:32:16 +04:00
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<h2>The API</h2>
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2000-06-02 17:27:59 +04:00
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<p>The interface to the SQLite library consists of 4 functions,
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one opaque data structure, and some constants used as return
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values from sqlite_exec():</p>
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2000-05-29 22:20:15 +04:00
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<blockquote><pre>
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typedef struct sqlite sqlite;
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2000-05-29 22:20:15 +04:00
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sqlite *sqlite_open(const char *filename, int mode, char **errmsg);
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2000-05-29 22:32:16 +04:00
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void sqlite_close(sqlite*);
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int sqlite_exec(
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sqlite*,
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char *sql,
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int (*)(void*,int,char**,char**),
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void*,
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char **errmsg
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);
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2000-05-29 22:20:15 +04:00
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int sqlite_complete(const char *sql);
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#define SQLITE_OK 0 /* Successful result */
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#define SQLITE_INTERNAL 1 /* An internal logic error in SQLite */
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#define SQLITE_ERROR 2 /* SQL error or missing database */
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#define SQLITE_PERM 3 /* Access permission denied */
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#define SQLITE_ABORT 4 /* Callback routine requested an abort */
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#define SQLITE_BUSY 5 /* One or more database files are locked */
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#define SQLITE_NOMEM 6 /* A malloc() failed */
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#define SQLITE_READONLY 7 /* Attempt to write a readonly database */
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2000-05-29 22:20:15 +04:00
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</pre></blockquote>
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<p>All of the above definitions are included in the "sqlite.h"
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header file that comes in the source tree.</p>
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<h2>Opening a database</h2>
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2000-06-02 17:27:59 +04:00
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<p>Use the <b>sqlite_open()</b> function to open an existing SQLite
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database or to create a new SQLite database. The first argument
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is the database name. The second argument is a constant 0666 to
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open the database for reading and writing and 0444 to open the
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database read only. The third argument is a pointer to a string
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pointer. If the third argument is not NULL and an error occurs
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while trying to open the database, then an error message will be
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written to memory obtained from malloc() and *errmsg will be made
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to point to this error message. The calling function is responsible
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for freeing the memory when it has finished with it.</p>
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<p>An SQLite database is just a directory containing a collection of
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GDBM files. There is one GDBM file for each table and index in the
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database. All GDBM files end with the ".tbl" suffix. Every SQLite
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database also contains a special database table named <b>sqlite_master</b>
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stored in its own GDBM file. This special table records the database
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schema.</p>
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<p>To create a new SQLite database, all you have to do is call
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<b>sqlite_open()</b> with the first parameter set to the name of
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an empty directory and the second parameter set to 0666.</p>
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<p>The return value of the <b>sqlite_open()</b> function is a
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pointer to an opaque <b>sqlite</b> structure. This pointer will
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be the first argument to all subsequent SQLite function calls that
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deal with the same database. NULL is returned if the open fails
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for any reason.</p>
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<h2>Closing the database</h2>
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<p>To close an SQLite database, just call the <b>sqlite_close()</b>
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function passing it the sqlite structure pointer that was obtained
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from a prior call to <b>sqlite_open</b>.
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<h2>Executing SQL statements</h2>
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<p>The <b>sqlite_exec()</b> function is used to process SQL statements
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and queries. This function requires 5 parameters as follows:</p>
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<ol>
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<li><p>A pointer to the sqlite structure obtained from a prior call
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to <b>sqlite_open()</b>.</p></li>
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<li><p>A null-terminated string containing the text of one or more
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SQL statements and/or queries to be processed.</p></li>
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<li><p>A pointer to a callback function which is invoked once for each
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row in the result of a query. This argument may be NULL, in which
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case no callbacks will ever be invoked.</p></li>
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<li><p>A pointer that is forwarded to become the first argument
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to the callback function.</p></li>
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<li><p>A pointer to an error string. Error messages are written to space
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obtained from malloc() and the error string is made to point to
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the malloced space. The calling function is responsible for freeing
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this space when it has finished with it.
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This argument may be NULL, in which case error messages are not
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reported back to the calling function.</p></li>
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</ol>
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<p>
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The callback function is used to receive the results of a query. A
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prototype for the callback function is as follows:</p>
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<blockquote><pre>
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int Callback(void *pArg, int argc, char **argv, char **columnNames){
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return 0;
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}
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</pre></blockquote>
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<p>The first argument to the callback is just a copy of the fourth argument
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to <b>sqlite_exec()</b> This parameter can be used to pass arbitrary
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information through to the callback function from client code.
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The second argument is the number columns in the query result.
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The third argument is an array of pointers to strings where each string
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is a single column of the result for that record. Note that the
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callback function reports a NULL value in the database as a NULL pointer,
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which is very different from an empty string. If the i-th parameter
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is an empty string, we will get:</p>
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<blockquote><pre>
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argv[i][0] == 0
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</pre></blockquote>
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<p>But if the i-th parameter is NULL we will get:</p>
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<blockquote><pre>
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argv[i] == 0
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</pre></blockquote>
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<p>The names of the columns are contained in the fourth argument.</p>
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<p>The callback function should normally return 0. If the callback
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function returns non-zero, the query is immediately aborted and
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<b>sqlite_exec()</b> will return SQLITE_ABORT.</p>
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2000-05-29 22:20:15 +04:00
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<h2>Testing for a complete SQL statement</h2>
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<p>The last interface routine to SQLite is a convenience function used
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to test whether or not a string forms a complete SQL statement.
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If the <b>sqlite_complete()</b> function returns true when its input
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is a string, then the argument forms a complete SQL statement.
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There are no guarantees that the syntax of that statement is correct,
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but we at least know the statement is complete. If <b>sqlite_complete()</b>
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returns false, then more text is required to complete the SQL statement.</p>
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<p>For the purpose of the <b>sqlite_complete()</b> function, an SQL
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statement is complete if it ends in a semicolon.</p>
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2000-06-02 17:27:59 +04:00
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<p>The <b>sqlite</b> command-line utility uses the <b>sqlite_complete()</b>
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function to know when it needs to call <b>sqlite_exec()</b>. After each
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line of input is received, <b>sqlite</b> calls <b>sqlite_complete()</b>
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on all input in its buffer. If <b>sqlite_complete()</b> returns true,
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then <b>sqlite_exec()</b> is called and the input buffer is reset. If
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<b>sqlite_complete()</b> returns false, then the prompt is changed to
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the continuation prompt and another line of text is read and added to
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the input buffer.</p>
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2000-05-29 22:32:16 +04:00
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<h2>Usage Examples</h2>
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<p>For examples of how the SQLite C/C++ interface can be used,
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refer to the source code for the <b>sqlite</b> program in the
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file <b>src/shell.c</b> of the source tree.
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2000-06-02 17:27:59 +04:00
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Additional information about sqlite is available at
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<a href="sqlite.html">sqlite.html</a>.
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2000-05-29 22:32:16 +04:00
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See also the sources to the Tcl interface for SQLite in
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the source file <b>src/tclsqlite.c</b>.</p>
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}
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2000-05-29 22:20:15 +04:00
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puts {
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<p><hr /></p>
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<p><a href="index.html"><img src="/goback.jpg" border=0 />
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Back to the SQLite Home Page</a>
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</p>
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</body></html>}
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