SQLite

     to locate the check-in desired, click on its information page link,
     then click on the "Tarball" or "ZIP Archive" links on the information
     page.

If you do want to use Fossil to check out the source tree, 
first install Fossil version 2.0 or later.
(Source tarballs and precompiled binaries available
[here](https://www.fossil-scm.org/fossil/uv/download.html).  Fossil is
a stand-alone program.  To install, simply download or build the single 
executable file and put that file someplace on your $PATH.)
Then run commands like this:

        mkdir ~/sqlite
        cd ~/sqlite
        fossil clone https://www.sqlite.org/src sqlite.fossil
        fossil open sqlite.fossil
    

SQLite does not require [Tcl](http://www.tcl.tk/) to run, but a Tcl installation
is required by the makefiles (including those for MSVC).  SQLite contains
a lot of generated code and Tcl is used to do much of that code generation.
The makefiles also require AWK.

## Source Code Tour

Most of the core source files are in the **src/** subdirectory.  The
**src/** folder also contains files used to build the "testfixture" test
harness. The names of the source files used "by testfixture" all begin
with "test".
The **src/** also contains the "shell.c" file
which is the main program for the "sqlite3.exe"
[command-line shell](https://sqlite.org/cli.html) and
the "tclsqlite.c" file which implements the
[TCL bindings](https://sqlite.org/tclsqlite.html) for SQLite.
(Historical note:  SQLite began as a Tcl
extension and only later escaped to the wild as an independent library.)

Test scripts and programs are found in the **test/** subdirectory.
Addtional test code is found in other source repositories.
See [How SQLite Is Tested](http://www.sqlite.org/testing.html) for
additional information.


The **ext/** subdirectory contains code for extensions.  The
Full-text search engine is in **ext/fts3**.  The R-Tree engine is in
**ext/rtree**.  The **ext/misc** subdirectory contains a number of
smaller, single-file extensions, such as a REGEXP operator.

The **tool/** subdirectory contains various scripts and programs used

The "target_source" make target will create a subdirectory "tsrc/" and
fill it with all the source files needed to build SQLite, both
manually-edited files and automatically-generated files.

The SQLite interface is defined by the **sqlite3.h** header file, which is
generated from src/sqlite.h.in, ./manifest.uuid, and ./VERSION.  The
[Tcl script](http://www.tcl.tk) at tool/mksqlite3h.tcl does the conversion.
The manifest.uuid file contains the SHA3 hash of the particular check-in
and is used to generate the SQLITE\_SOURCE\_ID macro.  The VERSION file
contains the current SQLite version number.  The sqlite3.h header is really
just a copy of src/sqlite.h.in with the source-id and version number inserted
at just the right spots. Note that comment text in the sqlite3.h file is
used to generate much of the SQLite API documentation.  The Tcl scripts
used to generate that documentation are in a separate source repository.

opcode-number to opcode-name that is used for EXPLAIN output.

The **keywordhash.h** header file contains the definition of a hash table
that maps SQL language keywords (ex: "CREATE", "SELECT", "INDEX", etc.) into
the numeric codes used by the parse.c parser.  The keywordhash.h file is
generated by a C-language program at tool mkkeywordhash.c.

Th3 **pragma.h** header file contains various definitions used to parse
and implement the PRAGMA statements.  The header is generated by a
script **tool/mkpragmatab.tcl**. If you want to add a new PRAGMA, edit
the **tool/mkpragmatab.tcl** file to insert the information needed by the
parser for your new PRAGMA, then run the script to regenerate the
**pragma.h** header file.

### The Amalgamation

All of the individual C source code and header files (both manually-edited
and automatically-generated) can be combined into a single big source file
**sqlite3.c** called "the amalgamation".  The amalgamation is the recommended
way of using SQLite in a larger application.  Combining all individual
source code files into a single big source code file allows the C compiler
to perform more cross-procedure analysis and generate better code.  SQLite
runs about 5% faster when compiled from the amalgamation versus when compiled
from individual source files.

The amalgamation is generated from the tool/mksqlite3c.tcl Tcl script.
First, all of the individual source files must be gathered into the tsrc/
subdirectory (using the equivalent of "make target_source") then the
tool/mksqlite3c.tcl script is run to copy them all together in just the
right order while resolving internal "#include" references.

The amalgamation source file is more than 200K lines long.  Some symbolic
debuggers (most notably MSVC) are unable to deal with files longer than 64K
lines.  To work around this, a separate Tcl script, tool/split-sqlite3c.tcl,
can be run on the amalgamation to break it up into a single small C file
called **sqlite3-all.c** that does #include on about five other files
named **sqlite3-1.c**, **sqlite3-2.c**, ..., **sqlite3-5.c**.  In this way,
all of the source code is contained within a single translation unit so
that the compiler can do extra cross-procedure optimization, but no
individual source file exceeds 32K lines in length.

## How It All Fits Together

SQLite is modular in design.
See the [architectural description](http://www.sqlite.org/arch.html)
for details. Other documents that are useful in
(helping to understand how SQLite works include the
[file format](http://www.sqlite.org/fileformat2.html) description,
the [virtual machine](http://www.sqlite.org/opcode.html) that runs
prepared statements, the description of
[how transactions work](http://www.sqlite.org/atomiccommit.html), and
the [overview of the query planner](http://www.sqlite.org/optoverview.html).

Years of effort have gone into optimizating SQLite, both
for small size and high performance.  And optimizations tend to result in
complex code.  So there is a lot of complexity in the current SQLite
implementation.  It will not be the easiest library in the world to hack.

Key files:

  *  **sqlite.h.in** - This file defines the public interface to the SQLite
     library.  Readers will need to be familiar with this interface before
     trying to understand how the library works internally.

There are many other source files.  Each has a suscinct header comment that
describes its purpose and role within the larger system.


## Contacts

The main SQLite webpage is [http://www.sqlite.org/](http://www.sqlite.org/)
with geographically distributed backups at
[http://www2.sqlite.org/](http://www2.sqlite.org) and
[http://www3.sqlite.org/](http://www3.sqlite.org).