package Carp; our $VERSION = '1.03'; =head1 NAME carp - warn of errors (from perspective of caller) cluck - warn of errors with stack backtrace (not exported by default) croak - die of errors (from perspective of caller) confess - die of errors with stack backtrace shortmess - return the message that carp and croak produce longmess - return the message that cluck and confess produce =head1 SYNOPSIS use Carp; croak "We're outta here!"; use Carp qw(cluck); cluck "This is how we got here!"; print FH Carp::shortmess("This will have caller's details added"); print FH Carp::longmess("This will have stack backtrace added"); =head1 DESCRIPTION The Carp routines are useful in your own modules because they act like die() or warn(), but with a message which is more likely to be useful to a user of your module. In the case of cluck, confess, and longmess that context is a summary of every call in the call-stack. For a shorter message you can use carp, croak or shortmess which report the error as being from where your module was called. There is no guarantee that that is where the error was, but it is a good educated guess. You can also alter the way the output and logic of C works, by changing some global variables in the C namespace. See the section on C below. Here is a more complete description of how shortmess works. What it does is search the call-stack for a function call stack where it hasn't been told that there shouldn't be an error. If every call is marked safe, it then gives up and gives a full stack backtrace instead. In other words it presumes that the first likely looking potential suspect is guilty. Its rules for telling whether a call shouldn't generate errors work as follows: =over 4 =item 1. Any call from a package to itself is safe. =item 2. Packages claim that there won't be errors on calls to or from packages explicitly marked as safe by inclusion in @CARP_NOT, or (if that array is empty) @ISA. The ability to override what @ISA says is new in 5.8. =item 3. The trust in item 2 is transitive. If A trusts B, and B trusts C, then A trusts C. So if you do not override @ISA with @CARP_NOT, then this trust relationship is identical to, "inherits from". =item 4. Any call from an internal Perl module is safe. (Nothing keeps user modules from marking themselves as internal to Perl, but this practice is discouraged.) =item 5. Any call to Carp is safe. (This rule is what keeps it from reporting the error where you call carp/croak/shortmess.) =back =head2 Forcing a Stack Trace As a debugging aid, you can force Carp to treat a croak as a confess and a carp as a cluck across I modules. In other words, force a detailed stack trace to be given. This can be very helpful when trying to understand why, or from where, a warning or error is being generated. This feature is enabled by 'importing' the non-existent symbol 'verbose'. You would typically enable it by saying perl -MCarp=verbose script.pl or by including the string C in the PERL5OPT environment variable. Alternately, you can set the global variable C<$Carp::Verbose> to true. See the C section below. =cut # This package is heavily used. Be small. Be fast. Be good. # Comments added by Andy Wardley 09-Apr-98, based on an # _almost_ complete understanding of the package. Corrections and # comments are welcome. # The members of %Internal are packages that are internal to perl. # Carp will not report errors from within these packages if it # can. The members of %CarpInternal are internal to Perl's warning # system. Carp will not report errors from within these packages # either, and will not report calls *to* these packages for carp and # croak. They replace $CarpLevel, which is deprecated. The # $Max(EvalLen|(Arg(Len|Nums)) variables are used to specify how the eval # text and function arguments should be formatted when printed. # Comments added by Jos I. Boumans 11-Aug-2004 # I can not get %CarpInternal or %Internal to work as advertised, # therefor leaving it out of the below documentation. # $CarpLevel may be decprecated according to the last comment, but # after 6 years, it's still around and in heavy use ;) =pod =head1 GLOBAL VARIABLES =head2 $Carp::CarpLevel This variable determines how many call frames are to be skipped when reporting where an error occurred on a call to one of C's functions. For example: $Carp::CarpLevel = 1; sub bar { .... or _error('Wrong input') } sub _error { Carp::carp(@_) } This would make Carp report the error as coming from C's caller, rather than from C<_error>'s caller, as it normally would. Defaults to C<0>. =head2 $Carp::MaxEvalLen This variable determines how many characters of a string-eval are to be shown in the output. Use a value of C<0> to show all text. Defaults to C<0>. =head2 $Carp::MaxArgLen This variable determines how many characters of each argument to a function to print. Use a value of C<0> to show the full length of the argument. Defaults to C<64>. =head2 $Carp::MaxArgNums This variable determines how many arguments to each function to show. Use a value of C<0> to show all arguments to a function call. Defaults to C<8>. =head2 $Carp::Verbose This variable makes C use the C function at all times. This effectively means that all calls to C become C and all calls to C become C. Note, this is analogous to using C. Defaults to C<0>. =cut $CarpInternal{Carp}++; $CarpInternal{warnings}++; $CarpLevel = 0; # How many extra package levels to skip on carp. # How many calls to skip on confess. # Reconciling these notions is hard, use # %Internal and %CarpInternal instead. $MaxEvalLen = 0; # How much eval '...text...' to show. 0 = all. $MaxArgLen = 64; # How much of each argument to print. 0 = all. $MaxArgNums = 8; # How many arguments to print. 0 = all. $Verbose = 0; # If true then make shortmess call longmess instead require Exporter; @ISA = ('Exporter'); @EXPORT = qw(confess croak carp); @EXPORT_OK = qw(cluck verbose longmess shortmess); @EXPORT_FAIL = qw(verbose); # hook to enable verbose mode =head1 BUGS The Carp routines don't handle exception objects currently. If called with a first argument that is a reference, they simply call die() or warn(), as appropriate. =cut # if the caller specifies verbose usage ("perl -MCarp=verbose script.pl") # then the following method will be called by the Exporter which knows # to do this thanks to @EXPORT_FAIL, above. $_[1] will contain the word # 'verbose'. sub export_fail { shift; $Verbose = shift if $_[0] eq 'verbose'; return @_; } # longmess() crawls all the way up the stack reporting on all the function # calls made. The error string, $error, is originally constructed from the # arguments passed into longmess() via confess(), cluck() or shortmess(). # This gets appended with the stack trace messages which are generated for # each function call on the stack. sub longmess { { local $@; # XXX fix require to not clear $@? # don't use require unless we need to (for Safe compartments) require Carp::Heavy unless $INC{"Carp/Heavy.pm"}; } # Icky backwards compatibility wrapper. :-( my $call_pack = caller(); if ($Internal{$call_pack} or $CarpInternal{$call_pack}) { return longmess_heavy(@_); } else { local $CarpLevel = $CarpLevel + 1; return longmess_heavy(@_); } } # shortmess() is called by carp() and croak() to skip all the way up to # the top-level caller's package and report the error from there. confess() # and cluck() generate a full stack trace so they call longmess() to # generate that. In verbose mode shortmess() calls longmess() so # you always get a stack trace sub shortmess { # Short-circuit &longmess if called via multiple packages { local $@; # XXX fix require to not clear $@? # don't use require unless we need to (for Safe compartments) require Carp::Heavy unless $INC{"Carp/Heavy.pm"}; } # Icky backwards compatibility wrapper. :-( my $call_pack = caller(); local @CARP_NOT = caller(); shortmess_heavy(@_); } # the following four functions call longmess() or shortmess() depending on # whether they should generate a full stack trace (confess() and cluck()) # or simply report the caller's package (croak() and carp()), respectively. # confess() and croak() die, carp() and cluck() warn. sub croak { die shortmess @_ } sub confess { die longmess @_ } sub carp { warn shortmess @_ } sub cluck { warn longmess @_ } 1;