.. _lua-funcs-debug:

Debug Library
==============

Original document, see: http://www.lua.org/manual/5.1/manual.html

This library provides the functionality of the debug interface to Lua programs.
You should exert care when using this library. The functions provided here should
be used exclusively for debugging and similar tasks, such as profiling. Please
resist the temptation to use them as a usual programming tool: they can be very
slow. Moreover, several of these functions violate some assumptions about Lua
code (e.g., that variables local to a function cannot be accessed from outside or
that userdata metatables cannot be changed by Lua code) and therefore can
compromise otherwise secure code.

All functions in this library are provided inside the ``debug`` table. All
functions that operate over a thread have an optional first argument which is the
thread to operate over. The default is always the current thread.

.. index:: debug.debug (Lua)

.. _lua-func-debug.debug:

debug.debug
-----------------

.. function:: debug.debug ()

    Enters an interactive mode with the user, running each string that the user
    enters. Using simple commands and other debug facilities, the user can
    inspect global and local variables, change their values, evaluate expressions,
    and so on.
    A line containing only the word ``cont`` finishes this function, so that the
    caller continues its execution.

    Note that commands for ``debug.debug`` are not lexically nested  within any
    function, and so have no direct access to local variables.

.. index:: debug.getfenv (Lua)

.. _lua-func-debug.getfenv:

debug.getfenv
-----------------

.. function:: debug.getfenv (o)

    Returns the environment of object ``o``.

.. index:: debug.gethook (Lua)	

.. _lua-func-debug.gethook:

debug.gethook
-----------------

.. function:: debug.gethook ([thread])

    Returns the current hook settings of the thread, as three values: the current
    hook function, the current hook mask, and the current hook count (as set by
    the :ref:`lua-func-debug.sethook` function).
 
.. index:: debug.getinfo (Lua)	
 
.. _lua-func-debug.getinfo:

debug.getinfo
-----------------

.. function:: debug.getinfo ([thread,] function [, what])

    Returns a table with information about a function.
    You can give the function directly, or you can give a number as the value
    of ``function``, which means the function running at level ``function`` of
    the call stack of the given thread:
    level 0 is the current function (``getinfo`` itself);
    level 1 is the function that called ``getinfo``;
    and so on.
    If ``function`` is a number larger than the number of active functions,
    then ``getinfo`` returns **nil**.

    The returned table can contain all the fields returned by ``lua_getinfo``,
    with the string ``what`` describing which fields to fill in.
    The default for ``what`` is to get all information available,
    except the table of valid lines.
    If present,
    the option '``f``'
    adds a field named ``func`` with the function itself.
    If present,
    the option '``L``'
    adds a field named ``activelines`` with the table of
    valid lines.

    For instance, the expression ``debug.getinfo(1,"n").name`` returns
    a table with a name for the current function,
    if a reasonable name can be found,
    and the expression ``debug.getinfo(print)``
    returns a table with all available information
    about the :ref:`lua-func-print` function.

.. index:: debug.getlocal (Lua)	

.. _lua-func-debug.getlocal:

debug.getlocal
-----------------

.. function:: debug.getlocal ([thread,] level, local)

    This function returns the name and the value of the local variable
    with index ``local`` of the function at level ``level`` of the stack.
    (The first parameter or local variable has index 1, and so on,
    until the last active local variable.)
    The function returns **nil** if there is no local
    variable with the given index,
    and raises an error when called with a ``level`` out of range.
    (You can call :ref:`lua-func-debug.getinfo` to check whether the level is valid.)

    Variable names starting with '``(``' (open parentheses)
    represent internal variables
    (loop control variables, temporaries, and C function locals).

.. index:: debug.getmetatable (Lua)	

.. _lua-func-debug.getmetatable:

debug.getmetatable
-------------------

.. function:: debug.getmetatable (object)

    Returns the metatable of the given ``object`` or **nil** if it does not have
    a metatable.

.. index:: debug.getregistry (Lua)

.. _lua-func-debug.getregistry:

debug.getregistry
-----------------

.. function:: debug.getregistry ()

    Returns the registry table.

.. index:: debug.getupvalue (Lua)

.. _lua-func-debug.getupvalue:

debug.getupvalue
-----------------

.. function:: debug.getupvalue (func, up)

    This function returns the name and the value of the upvalue
    with index ``up`` of the function ``func``.
    The function returns **nil** if there is no upvalue with the given index.

.. index:: debug.setfenv (Lua)	

.. _lua-func-debug.setfenv:

debug.setfenv
-----------------

.. function:: debug.setfenv (object, table)

    Sets the environment of the given ``object`` to the given ``table``.
    Returns ``object``.

.. index:: debug.sethook (Lua)	

.. _lua-func-debug.sethook:

debug.sethook
-----------------

.. function:: debug.sethook ([thread,] hook, mask [, count])

    Sets the given function as a hook.
    The string ``mask`` and the number ``count`` describe
    when the hook will be called.
    The string mask may have the following characters,
    with the given meaning:

    * **``"c"``:** the hook is called every time Lua calls a function;
    * **``"r"``:** the hook is called every time Lua returns from a function;
    * **``"l"``:** the hook is called every time Lua enters a new line of code.

    With a ``count`` different from zero, the hook is called after every ``count``
    instructions.

    When called without arguments, :ref:`lua-func-debug.sethook` turns off the hook.

    When the hook is called, its first parameter is a string
    describing the event that has triggered its call:
    ``"call"``, ``"return"`` (or ``"tail return"``,
    when simulating a return from a tail call),
    ``"line"``, and ``"count"``.
    For line events,
    the hook also gets the new line number as its second parameter.
    Inside a hook,
    you can call ``getinfo`` with level 2 to get more information about
    the running function
    (level 0 is the ``getinfo`` function,
    and level 1 is the hook function),
    unless the event is ``"tail return"``.
    In this case, Lua is only simulating the return,
    and a call to ``getinfo`` will return invalid data.
    
.. index:: debug.setlocal (Lua)	
    
.. _lua-func-debug.setlocal:

debug.setlocal
-----------------

.. function:: debug.setlocal ([thread,] level, local, value)

    This function assigns the value ``value`` to the local variable
    with index ``local`` of the function at level ``level`` of the stack.
    The function returns **nil** if there is no local
    variable with the given index,
    and raises an error when called with a ``level`` out of range.
    (You can call ``getinfo`` to check whether the level is valid.)
    Otherwise, it returns the name of the local variable.

.. index:: debug.setmetatable (Lua)	

.. _lua-func-debug.setmetatable:

debug.setmetatable
-------------------

.. function:: debug.setmetatable (object, table)

    Sets the metatable for the given ``object`` to the given ``table``
    (which can be **nil**).

.. index:: debug.setupvalue (Lua)

.. _lua-func-debug.setupvalue:

debug.setupvalue
-----------------

.. function:: debug.setupvalue (func, up, value)

    This function assigns the value ``value`` to the upvalue
    with index ``up`` of the function ``func``.
    The function returns **nil** if there is no upvalue
    with the given index.
    Otherwise, it returns the name of the upvalue.

.. index:: debug.traceback (Lua)

.. _lua-func-debug.traceback:

debug.traceback
-----------------

.. function:: debug.traceback ([thread,] [message [, level]])

    Returns a string with a traceback of the call stack.
    An optional ``message`` string is appended
    at the beginning of the traceback.
    An optional ``level`` number tells at which level
    to start the traceback
    (default is 1, the function calling ``traceback``).

:sub:`id-165485`