| Current Path : /proc/3/task/3/root/proc/2/cwd/usr/share/perl5/ |
| Current File : //proc/3/task/3/root/proc/2/cwd/usr/share/perl5/Carp.pm |
package Carp;
our $VERSION = '1.11';
# 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<carp>
or C<croak> 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<Carp> works, by
changing some global variables in the C<Carp> namespace. See the
section on C<GLOBAL VARIABLES> below.
Here is a more complete description of how C<carp> and C<croak> 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<carp> or C<croak>.)
=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<all> 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<-MCarp=verbose> in the PERL5OPT
environment variable.
Alternately, you can set the global variable C<$Carp::Verbose> to true.
See the C<GLOBAL VARIABLES> 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<carp> and C<cluck> generate stack backtraces
just like C<cluck> and C<confess>. This is how C<use Carp 'verbose'>
is implemented internally.
Defaults to C<0>.
=head2 %Carp::Internal
This says what packages are internal to Perl. C<Carp> 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<carp> or C<croak>. There errors
will not be reported on any lines that are calling packages in
C<%Carp::CarpInternal>.
For example C<Carp> itself is listed in C<%Carp::CarpInternal>.
Therefore the full stack backtrace from C<confess> will not start
inside of C<Carp>, and the short message from calling C<croak> is
not placed on the line where C<croak> was called.
=head2 $Carp::CarpLevel
This variable determines how many additional call frames are to be
skipped that would not otherwise be when reporting where an error
occurred on a call to one of C<Carp>'s functions. It is fairly easy
to count these call frames on calls that generate a full stack
backtrace. However it is much harder to do this accounting for calls
that generate a short message. Usually people skip too many call
frames. If they are lucky they skip enough that C<Carp> goes all of
the way through the call stack, realizes that something is wrong, and
then generates a full stack backtrace. If they are unlucky then the
error is reported from somewhere misleading very high in the call
stack.
Therefore it is best to avoid C<$Carp::CarpLevel>. Instead use
C<@CARP_NOT>, C<%Carp::Internal> and C<%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.
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