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.
debug.debug¶
- 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.
debug.getfenv¶
- debug.getfenv(o)¶
Returns the environment of object
o
.
debug.gethook¶
- 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 debug.sethook function).
debug.getinfo¶
- 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 levelfunction
of the call stack of the given thread: level 0 is the current function (getinfo
itself); level 1 is the function that calledgetinfo
; and so on. Iffunction
is a number larger than the number of active functions, thengetinfo
returns nil.The returned table can contain all the fields returned by
lua_getinfo
, with the stringwhat
describing which fields to fill in. The default forwhat
is to get all information available, except the table of valid lines. If present, the option ‘f
’ adds a field namedfunc
with the function itself. If present, the option ‘L
’ adds a field namedactivelines
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 expressiondebug.getinfo(print)
returns a table with all available information about the print function.
debug.getlocal¶
- debug.getlocal([thread, ]level, local)¶
This function returns the name and the value of the local variable with index
local
of the function at levellevel
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 alevel
out of range. (You can call 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).
debug.getmetatable¶
- debug.getmetatable(object)¶
Returns the metatable of the given
object
or nil if it does not have a metatable.
debug.getregistry¶
- debug.getregistry()¶
Returns the registry table.
debug.getupvalue¶
- debug.getupvalue(func, up)¶
This function returns the name and the value of the upvalue with index
up
of the functionfunc
. The function returns nil if there is no upvalue with the given index.
debug.setfenv¶
- debug.setfenv(object, table)¶
Sets the environment of the given
object
to the giventable
. Returnsobject
.
debug.sethook¶
- debug.sethook([thread, ]hook, mask[, count])¶
Sets the given function as a hook. The string
mask
and the numbercount
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 everycount
instructions.When called without arguments, 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 callgetinfo
with level 2 to get more information about the running function (level 0 is thegetinfo
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 togetinfo
will return invalid data.
debug.setlocal¶
- debug.setlocal([thread, ]level, local, value)¶
This function assigns the value
value
to the local variable with indexlocal
of the function at levellevel
of the stack. The function returns nil if there is no local variable with the given index, and raises an error when called with alevel
out of range. (You can callgetinfo
to check whether the level is valid.) Otherwise, it returns the name of the local variable.
debug.setmetatable¶
- debug.setmetatable(object, table)¶
Sets the metatable for the given
object
to the giventable
(which can be nil).
debug.setupvalue¶
- debug.setupvalue(func, up, value)¶
This function assigns the value
value
to the upvalue with indexup
of the functionfunc
. The function returns nil if there is no upvalue with the given index. Otherwise, it returns the name of the upvalue.
debug.traceback¶
- 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 optionallevel
number tells at which level to start the traceback (default is 1, the function callingtraceback
).
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