base (version 3.6.0)

traceback: 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 deparsed 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("deparse.max.lines"))
.traceback(x = NULL)

Arguments

x

NULL (default, meaning .Traceback), or an integer count of calls to skip in the current stack, or a list or pairlist of deparsed calls. See the details.

max.lines

The maximum number of lines to be printed per call. The default is unlimited.

Value

traceback() prints the deparsed call stack deepest call first, and returns it invisibly. The calls may print on more than one line, and the first line for each call is labelled by the frame number. The number of lines printed per call can be limited via max.lines.

Warning

It is undocumented where .Traceback is stored nor that it is visible, and this is subject to change.

Details

The default display is of the stack of the last uncaught error as stored as a list of deparsed calls in .Traceback, which traceback prints in a user-friendly format. The stack of deparsed 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(2)) will print the stack at the time of the error, skipping the call to traceback() and the error function that called it.

Otherwise, x is assumed to be a list or pairlist of deparsed calls and will be displayed in the same way.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

Examples

# NOT RUN {
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()
# }
# NOT RUN {
<!-- %dont -->
# }
# 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(2))
# }