365 lines
14 KiB
Tcl
365 lines
14 KiB
Tcl
set rcsid {$Id: capi3.tcl,v 1.1 2004/05/31 18:22:26 drh Exp $}
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source common.tcl
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header {C/C++ Interface For SQLite Version 3}
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puts {
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<h2>C/C++ Interface For SQLite Version 3</h2>
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<h3>1.0 Overview</h3>
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<p>
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SQLite version 3.0 will be a new version of SQLite, derived from
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the SQLite 2.8.13 code base, but with an incompatible file format
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and API.
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SQLite version 3.0 is intended to answer the increasing demand
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for the following features:
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</p>
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<ul>
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<li>Support for UTF-16.</li>
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<li>User-definable text collating sequences.</li>
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<li>The ability to store BLOBs in indexed columns.</li>
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</ul>
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<p>
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It became necessary to move to version 3.0
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to implement these features because each
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requires incompatible changes to the database file format. Other
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incompatible changes, such as a cleanup of the API, were introduced
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at the same time under the theory that it is best to get your
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incompatible changes out of the way all at once.
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<p>
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The API for version 3.0 is similar to the version 2.X API,
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but with some important changes. Most noticeably, the "<tt>sqlite_</tt>"
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prefix that occurs on the beginning of all API functions and data
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structures will be changed to "<tt>sqlite3_</tt>".
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This will avoid confusion between the two APIs and allow
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linking against both SQLite 2.X and SQLite 3.0 at the same time,
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if desired.
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</p>
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<p>
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There is no agreement on what the C datatype for a UTF-16
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string should be. Therefore, SQLite uses a generic type of void*
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to refer to UTF-16 strings.
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Client software can cast the void*
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to whatever datatype is appropriate for their system.
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</p>
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<h3>2.0 C/C++ Interface</h3>
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<h4>2.1 Opening and closing a database</h4>
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<blockquote><pre>
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typedef struct sqlite3 sqlite3;
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int sqlite3_open(const char*, sqlite3**, const char**);
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int sqlite3_open16(const void*, sqlite3**, const char**);
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int sqlite3_close(sqlite3*);
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const char *sqlite3_errmsg(sqlite3*);
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const void *sqlite3_errmsg16(sqlite3*);
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int sqlite3_errcode(sqlite3*);
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</pre></blockquote>
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<p>
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The sqlite3_open() routine returns an integer error code rather than
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a pointer to the sqlite3 structure. The difference between sqlite3_open()
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and sqlite3_open16() is that sqlite3_open16() takes UTF-16 (in host native
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byte order) for the name of the database file. If a new database file
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needs to be created, then sqlite3_open16() will set the internal text
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representation to UTF-16 whereas sqlite3_open() will set the text
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representation to UTF-8.
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</p>
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<p>
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The third "const char**" argument to sqlite3_open() is a NULL-terminated
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list of keyword/value pairs that define options to apply to the open
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request. The third argument may be NULL if there are no options.
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This extra argument provides an expandable way of supporting new features
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in future releases. For example, a future release may contain an
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option to define an encryption/decryption key.
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</p>
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<p>
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The sqlite3_errcode() routine will return the result code for the most
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recent major API call. sqlite3_errmsg() will return an English-language
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text error message for the most recent error. The error message will
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be represented in UTF-8 and will be ephemeral - it could disappear on
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the next call to any SQLite API function. sqlite3_errmsg16() works like
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sqlite3_errmsg() except that it returns the error message represented
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as UTF-16 in host native byte order.
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</p>
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<h4>2.2 Executing SQL statements</h4>
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<blockquote><pre>
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typedef struct sqlite3_stmt sqlite3_stmt;
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int sqlite3_prepare(sqlite3*, const char*, sqlite3_stmt**, const char**);
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int sqlite3_prepare16(sqlite3*, const void*, sqlite3_stmt**, const void**);
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int sqlite3_finalize(sqlite3_stmt*);
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int sqlite3_reset(sqlite3_stmt*);
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</pre></blockquote>
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<p>
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The non-callback API is now the preferred way of accessing the database.
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Wrapper functions that emulate the older callback API may (or may not)
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be provided.
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</p>
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<p>
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The sqlite3_prepare() function compiles an single SQL statement.
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The statement may contain tokens of the form "?" or "?nnn" or ":nnn:"
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where "nnn" is an integer. Such tokens represent unspecified literal values
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(or wildcard) to be filled in later by the sqlite3_bind() API.
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Each wildcard as an associated number given
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by the "nnn" that follows the "?". If the "?" is not followed by an
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integer, then its number one more than the number of prior wildcards
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in the same SQL statement. It is allowed for the same wildcard
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to occur more than once in the same SQL statement, in which case
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all instance of that wildcard will be filled in with the same value.
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Unbound wildcards have a value of NULL.
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</p>
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<p>The SQL statement is a UTF-8 string for sqlite3_prepare().
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The sqlite3_prepare16() works the same way except
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that it expects a UTF-16 string as SQL input.
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Only the first SQL statement in the input string is compiled.
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The fourth parameter is filled in with a pointer to the next (uncompiled)
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SQLite statement in the input string, if any.
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The sqlite3_finalize() routine deallocates a prepared SQL statement.
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The sqlite3_reset() routine resets a prepared SQL statement so that it
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can be executed again.
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</p>
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<blockquote><pre>
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int sqlite3_bind_blob(sqlite3_stmt*, int, const void*, int n, int eCopy);
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int sqlite3_bind_double(sqlite3_stmt*, int, double);
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int sqlite3_bind_int(sqlite3_stmt*, int, int);
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int sqlite3_bind_int64(sqlite3_stmt*, int, long long int);
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int sqlite3_bind_null(sqlite3_stmt*, int);
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int sqlite3_bind_text(sqlite3_stmt*, int, const char*, int n, int eCopy);
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int sqlite3_bind_text16(sqlite3_stmt*, int, const void*, int n, int eCopy);
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int sqlite3_bind_value(sqlite3_stmt*, int, const sqlite3_value*);
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</pre></blockquote>
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<p>
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There is an assortment of sqlite3_bind routines used to assign values
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to wildcards in a prepared SQL statement. Unbound wildcards
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are interpreted as NULLs. Bindings are not reset by sqlite3_reset().
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But wildcards can be rebound to new values after an sqlite3_reset().
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</p>
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<p>
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After an SQL statement has been prepared (and optionally bound), it
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is executed using:
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</p>
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<blockquote><pre>
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int sqlite3_step(sqlite3_stmt*);
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</pre></blockquote>
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<p>
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The sqlite3_step() routine return SQLITE3_ROW if it is returning a single
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row of the result set, or SQLITE3_DONE if execution has completed, either
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normally or due to an error. It might also return SQLITE3_BUSY if it is
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unable to open the database file. If the return value is SQLITE3_ROW, then
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the following routines can be used to extract information about that row
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of the result set:
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</p>
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<blockquote><pre>
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int sqlite3_column_count(sqlite3_stmt*);
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int sqlite3_column_type(sqlite3_stmt*,int);
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const char *sqlite3_column_decltype(sqlite3_stmt *, int i);
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const char *sqlite3_column_decltype16(sqlite3_stmt *, int i);
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const char *sqlite3_column_name(sqlite3_stmt*,int);
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const void *sqlite3_column_name16(sqlite3_stmt*,int);
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const void *sqlite3_column_blob(sqlite3_stmt*, int iCol);
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int sqlite3_column_bytes(sqlite3_stmt*, int iCol);
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int sqlite3_column_bytes16(sqlite3_stmt*, int iCol);
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double sqlite3_column_double(sqlite3_stmt*, int iCol);
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int sqlite3_column_int(sqlite3_stmt*, int iCol);
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long long int sqlite3_column_int64(sqlite3_stmt*, int iCol);
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const unsigned char *sqlite3_column_text(sqlite3_stmt*, int iCol);
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const void *sqlite3_column_text16(sqlite3_stmt*, int iCol);
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int sqlite3_column_type(sqlite3_stmt*, int iCol);
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</pre></blockquote>
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<p>
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The sqlite3_column_count() function returns the number of columns in
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the results set. The sqlite3_column_type() function returns the
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datatype for the value in the Nth column. The return value is one
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of these:
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</p>
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<blockquote><pre>
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#define SQLITE3_INTEGER 1
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#define SQLITE3_FLOAT 2
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#define SQLITE3_TEXT 3
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#define SQLITE3_BLOB 4
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#define SQLITE3_NULL 5
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</pre></blockquote>
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<p>
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The sqlite3_column_decltype() routine returns text which is the
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declared type of the column in the CREATE TABLE statement. For an
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expression, the return type is an empty string. sqlite3_column_name()
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returns the name of the Nth column. sqlite3_column_bytes() returns
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the number of bytes in a column that has type BLOB or the number of bytes
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in a TEXT string with UTF-8 encoding. sqlite3_column_bytes16() returns
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the same value for BLOBs but for TEXT strings returns the number of bytes
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in a UTF-16 encoding.
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sqlite3_column_blob() return BLOB data.
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sqlite3_column_text() return TEXT data as UTF-8.
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sqlite3_column_text16() return TEXT data as UTF-16.
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sqlite3_column_int() return INTEGER data in the host machines native
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integer format.
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sqlite3_column_int64() returns 64-bit INTEGER data.
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Finally, sqlite3_column_double() return floating point data.
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</p>
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<h4>2.3 User-defined functions</h4>
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<p>
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User defined functions can be created using the following routine:
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</p>
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<blockquote><pre>
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typedef struct sqlite3_value sqlite3_value;
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int sqlite3_create_function(
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sqlite3 *,
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const char *zFunctionName,
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int nArg,
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int eTextRep,
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int iCollateArg,
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void*,
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void (*xFunc)(sqlite3_context*,int,sqlite3_value**),
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void (*xStep)(sqlite3_context*,int,sqlite3_value**),
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void (*xFinal)(sqlite3_context*)
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);
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int sqlite3_create_function16(
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sqlite3*,
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const void *zFunctionName,
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int nArg,
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int eTextRep,
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int iCollateArg,
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void*,
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void (*xFunc)(sqlite3_context*,int,sqlite3_value**),
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void (*xStep)(sqlite3_context*,int,sqlite3_value**),
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void (*xFinal)(sqlite3_context*)
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);
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#define SQLITE3_UTF8 1
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#define SQLITE3_UTF16LE 2
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#define SQLITE3_UTF16BE 3
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#define SQLITE3_ANY 4
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</pre></blockquote>
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<p>
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The nArg parameter specifies the number of arguments to the function.
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A value of 0 indicates that any number of arguments is allowed. The
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eTextRep parameter specifies what representation text values are expected
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to be in for arguments to this function. The value of this parameter should
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be one of the parameters defined above. SQLite version 3 allows multiple
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implementations of the same function using different text representations.
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The database engine chooses the function that minimization the number
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of text conversions required.
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The iCollateArg parameter indicates that the collating sequence for the
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result is to be the same as the collating sequence of the iCollateArg-th
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parameter.
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</p>
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<p>
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Normal functions specify only xFunc and leave xStep and xFinal set to NULL.
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Aggregate functions specify xStep and xFinal and leave xFunc set to NULL.
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There is no separate sqlite3_create_aggregate() API.
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</p>
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<p>
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The function name is specified in UTF-8. A separate sqlite3_create_function16()
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API works the same as sqlite_create_function()
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except that the function name is specified in UTF-16 host byte order.
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</p>
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<p>
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Notice that the parameters to functions are now pointers to sqlite3_value
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structures instead of pointers to strings as in SQLite version 2.X.
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The following routines are used to extract useful information from these
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"values":
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</p>
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<blockquote><pre>
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const void *sqlite3_value_blob(sqlite3_value*);
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int sqlite3_value_bytes(sqlite3_value*);
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int sqlite3_value_bytes16(sqlite3_value*);
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double sqlite3_value_double(sqlite3_value*);
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int sqlite3_value_int(sqlite3_value*);
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long long int sqlite3_value_int64(sqlite3_value*);
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const unsigned char *sqlite3_value_text(sqlite3_value*);
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const void *sqlite3_value_text16(sqlite3_value*);
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int sqlite3_value_type(sqlite3_value*);
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</pre></blockquote>
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<p>
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Function implementations use the following APIs to acquire context and
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to report results:
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</p>
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<blockquote><pre>
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void *sqlite3_aggregate_context(sqlite3_context*, int nbyte);
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void *sqlite3_user_data(sqlite3_context*);
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void sqlite3_result_blob(sqlite3_context*, const void*, int n, int eCopy);
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void sqlite3_result_double(sqlite3_context*, double);
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void sqlite3_result_error(sqlite3_context*, const char*, int);
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void sqlite3_result_error16(sqlite3_context*, const void*, int);
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void sqlite3_result_int(sqlite3_context*, int);
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void sqlite3_result_int64(sqlite3_context*, long long int);
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void sqlite3_result_null(sqlite3_context*);
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void sqlite3_result_text(sqlite3_context*, const char*, int n, int eCopy);
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void sqlite3_result_text16(sqlite3_context*, const void*, int n, int eCopy);
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void sqlite3_result_value(sqlite3_context*, sqlite3_value*);
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void *sqlite3_get_auxdata(sqlite3_context*, int);
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void sqlite3_set_auxdata(sqlite3_context*, int, void*, void (*)(void*));
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</pre></blockquote>
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<h4>2.4 User-defined collating sequences</h4>
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<p>
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The following routines are used to implement user-defined
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collating sequences:
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</p>
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<blockquote><pre>
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sqlite3_create_collation(sqlite3*, const char *zName, int eTextRep, void*,
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int(*xCompare)(void*,int,const void*,int,const void*));
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sqlite3_create_collation16(sqlite3*, const void *zName, int eTextRep, void*,
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int(*xCompare)(void*,int,const void*,int,const void*));
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sqlite3_collation_needed(sqlite3*, void*,
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void(*)(void*,sqlite3*,int eTextRep,const char*));
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sqlite3_collation_needed16(sqlite3*, void*,
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void(*)(void*,sqlite3*,int eTextRep,const void*));
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</pre></blockquote>
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<p>
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The sqlite3_create_collation() function specifies a collating sequence name
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and a comparison function to implement that collating sequence. The
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comparison function is only used for comparing text values. The eTextRep
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parameter is one of SQLITE3_UTF8, SQLITE3_UTF16LE, SQLITE3_UTF16BE, or
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SQLITE3_ANY to specify which text representation to comparison function works
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with. Separate comparison functions can exist for the same collating
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sequence for each of the UTF-8, UTF-16LE and UTF-16BE text representations.
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The sqlite3_create_collation16() works like sqlite3_create_collation() except
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that the collation name is specified in UTF-16 host byte order instead of
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in UTF-8.
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</p>
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<p>
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The sqlite3_collation_needed() routine registers a callback which the
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database engine will invoke if it encounters an unknown collating sequence.
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The callback can lookup an appropriate comparison function and invoke
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sqlite_3_create_collation() as needed. The fourth parameter to the callback
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is the name of the collating sequence in UTF-8. For sqlite3_collation_need16()
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the callback sends the collating sequence name in UTF-16 host byte order.
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</p>
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}
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footer $rcsid
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