| traceback {base} | R Documentation |
Get and Print Call Stacks
Description
By default traceback() prints the call stack of the last
uncaught error, i.e., the sequence of calls that lead to the error.
This is useful when an error occurs with an unidentifiable error
message. It can also be used to print the current stack or
arbitrary lists of calls.
.traceback() now returns the above call stack (and
traceback(x, *) can be regarded as convenience function for
printing the result of .traceback(x)).
Usage
traceback(x = NULL, max.lines = getOption("traceback.max.lines",
getOption("deparse.max.lines", -1L)))
.traceback(x = NULL, max.lines = getOption("traceback.max.lines",
getOption("deparse.max.lines", -1L)))
Arguments
x |
|
max.lines |
a number, the maximum number of lines to be printed
per call. The default is unlimited. Applies only when |
Details
The default display is of the stack of the last uncaught error as
stored as a list of calls in .Traceback, which
traceback prints in a user-friendly format. The stack of
calls always contains all function calls and all foreign
function calls (such as .Call): if profiling is in
progress it will include calls to some primitive functions. (Calls
to builtins are included, but not to specials.)
Errors which are caught via try or
tryCatch do not generate a traceback, so what is printed
is the call sequence for the last uncaught error, and not necessarily
for the last error.
If x is numeric, then the current stack is printed, skipping
x entries at the top of the stack. For example,
options(error = function() traceback(3)) will print the stack
at the time of the error, skipping the call to traceback() and
.traceback()
and the error function that called it.
Otherwise, x is assumed to be a list or pairlist of calls or
deparsed calls and will be displayed in the same way.
.traceback() and by extension traceback() may trigger
deparsing of calls. This is an expensive operation
for large calls so it may be advisable to set max.lines
to a reasonable value when such calls are on the call stack.
Value
.traceback() returns the deparsed call stack deepest call
first as a list or pairlist. The number of lines deparsed from
the call can be limited via max.lines. Calls for which
max.lines results in truncated output will gain a
"truncated" attribute.
traceback() formats, prints, and returns the call stack
produced by .traceback() invisibly.
Warning
It is undocumented where .Traceback is stored nor that it is
visible, and this is subject to change. Currently
.Traceback contains the calls as language
objects.
References
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
Examples
foo <- function(x) { print(1); bar(2) }
bar <- function(x) { x + a.variable.which.does.not.exist }
## Not run:
foo(2) # gives a strange error
traceback()
## End(Not run)
## 2: bar(2)
## 1: foo(2)
bar
## Ah, this is the culprit ...
## This will print the stack trace at the time of the error.
options(error = function() traceback(3))