package Carp; our $VERSION = '1.07'; # this file is an utra-lightweight stub. The first time a function is # called, Carp::Heavy is loaded, and the real short/longmessmess_jmp # subs are installed our $MaxEvalLen = 0; our $Verbose = 0; our $CarpLevel = 0; our $MaxArgLen = 64; # How much of each argument to print. 0 = all. our $MaxArgNums = 8; # How many arguments to print. 0 = all. require Exporter; our @ISA = ('Exporter'); our @EXPORT = qw(confess croak carp); our @EXPORT_OK = qw(cluck verbose longmess shortmess); our @EXPORT_FAIL = qw(verbose); # hook to enable verbose mode # 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 $_[0] eq 'verbose'; @_ } # fixed hooks for stashes to point to sub longmess { goto &longmess_jmp } sub shortmess { goto &shortmess_jmp } # these two are replaced when Carp::Heavy is loaded sub longmess_jmp { local($@, $!); eval { require Carp::Heavy }; return $@ if $@; goto &longmess_real; } sub shortmess_jmp { local($@, $!); eval { require Carp::Heavy }; return $@ if $@; goto &shortmess_real; } sub croak { die shortmess @_ } sub confess { die longmess @_ } sub carp { warn shortmess @_ } sub cluck { warn longmess @_ } 1; __END__ =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 =head1 SYNOPSIS use Carp; croak "We're outta here!"; use Carp qw(cluck); cluck "This is how we got here!"; =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 C or C 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 c and c work. What they do is search the call-stack for a function call stack where they have not been told that there shouldn't be an error. If every call is marked safe, they give up and give a full stack backtrace instead. In other words they presume that the first likely looking potential suspect is guilty. Their 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 C<@CARP_NOT>, or (if that array is empty) C<@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 C<@ISA> with C<@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 Perl's warning system (eg Carp itself) is safe. (This rule is what keeps it from reporting the error at the point where you call C or C.) =item 6. C<$Carp::CarpLevel> can be set to skip a fixed number of additional call levels. Using this is not recommended because it is very difficult to get it to behave correctly. =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. =head1 GLOBAL VARIABLES =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 and C generate stack backtraces just like C and C. This is how C is implemented internally. Defaults to C<0>. =head2 %Carp::Internal This says what packages are internal to Perl. C will never report an error as being from a line in a package that is internal to Perl. For example: $Carp::Internal{ __PACKAGE__ }++; # time passes... sub foo { ... or confess("whatever") }; would give a full stack backtrace starting from the first caller outside of __PACKAGE__. (Unless that package was also internal to Perl.) =head2 %Carp::CarpInternal This says which packages are internal to Perl's warning system. For generating a full stack backtrace this is the same as being internal to Perl, the stack backtrace will not start inside packages that are listed in C<%Carp::CarpInternal>. But it is slightly different for the summary message generated by C or C. There errors will not be reported on any lines that are calling packages in C<%Carp::CarpInternal>. For example C itself is listed in C<%Carp::CarpInternal>. Therefore the full stack backtrace from C will not start inside of C, and the short message from calling C is not placed on the line where C was called. =head2 $Carp::CarpLevel This variable determines how many additional call frames are to be skipped that would not otherwise be when reporting where an error occurred on a call to one of C's functions. It is fairly easy to count these call frames on calls that generate a full stack backtrace. However it is much harder to do this accounting for calls that generate a short message. Usually people skip too many call frames. If they are lucky they skip enough that C goes all of the way through the call stack, realizes that something is wrong, and then generates a full stack backtrace. If they are unlucky then the error is reported from somewhere misleading very high in the call stack. Therefore it is best to avoid C<$Carp::CarpLevel>. Instead use C<@CARP_NOT>, C<%Carp::Internal> and %Carp::CarpInternal>. Defaults to C<0>. =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.