1package Carp; 2 3our $VERSION = '1.04'; 4 5=head1 NAME 6 7carp - warn of errors (from perspective of caller) 8 9cluck - warn of errors with stack backtrace 10 (not exported by default) 11 12croak - die of errors (from perspective of caller) 13 14confess - die of errors with stack backtrace 15 16shortmess - return the message that carp and croak produce 17 18longmess - return the message that cluck and confess produce 19 20=head1 SYNOPSIS 21 22 use Carp; 23 croak "We're outta here!"; 24 25 use Carp qw(cluck); 26 cluck "This is how we got here!"; 27 28 print FH Carp::shortmess("This will have caller's details added"); 29 print FH Carp::longmess("This will have stack backtrace added"); 30 31=head1 DESCRIPTION 32 33The Carp routines are useful in your own modules because 34they act like die() or warn(), but with a message which is more 35likely to be useful to a user of your module. In the case of 36cluck, confess, and longmess that context is a summary of every 37call in the call-stack. For a shorter message you can use carp, 38croak or shortmess which report the error as being from where 39your module was called. There is no guarantee that that is where 40the error was, but it is a good educated guess. 41 42You can also alter the way the output and logic of C<Carp> works, by 43changing some global variables in the C<Carp> namespace. See the 44section on C<GLOBAL VARIABLES> below. 45 46Here is a more complete description of how shortmess works. What 47it does is search the call-stack for a function call stack where 48it hasn't been told that there shouldn't be an error. If every 49call is marked safe, it then gives up and gives a full stack 50backtrace instead. In other words it presumes that the first likely 51looking potential suspect is guilty. Its rules for telling whether 52a call shouldn't generate errors work as follows: 53 54=over 4 55 56=item 1. 57 58Any call from a package to itself is safe. 59 60=item 2. 61 62Packages claim that there won't be errors on calls to or from 63packages explicitly marked as safe by inclusion in @CARP_NOT, or 64(if that array is empty) @ISA. The ability to override what 65@ISA says is new in 5.8. 66 67=item 3. 68 69The trust in item 2 is transitive. If A trusts B, and B 70trusts C, then A trusts C. So if you do not override @ISA 71with @CARP_NOT, then this trust relationship is identical to, 72"inherits from". 73 74=item 4. 75 76Any call from an internal Perl module is safe. (Nothing keeps 77user modules from marking themselves as internal to Perl, but 78this practice is discouraged.) 79 80=item 5. 81 82Any call to Carp is safe. (This rule is what keeps it from 83reporting the error where you call carp/croak/shortmess.) 84 85=back 86 87=head2 Forcing a Stack Trace 88 89As a debugging aid, you can force Carp to treat a croak as a confess 90and a carp as a cluck across I<all> modules. In other words, force a 91detailed stack trace to be given. This can be very helpful when trying 92to understand why, or from where, a warning or error is being generated. 93 94This feature is enabled by 'importing' the non-existent symbol 95'verbose'. You would typically enable it by saying 96 97 perl -MCarp=verbose script.pl 98 99or by including the string C<MCarp=verbose> in the PERL5OPT 100environment variable. 101 102Alternately, you can set the global variable C<$Carp::Verbose> to true. 103See the C<GLOBAL VARIABLES> section below. 104 105=cut 106 107# This package is heavily used. Be small. Be fast. Be good. 108 109# Comments added by Andy Wardley <abw@kfs.org> 09-Apr-98, based on an 110# _almost_ complete understanding of the package. Corrections and 111# comments are welcome. 112 113# The members of %Internal are packages that are internal to perl. 114# Carp will not report errors from within these packages if it 115# can. The members of %CarpInternal are internal to Perl's warning 116# system. Carp will not report errors from within these packages 117# either, and will not report calls *to* these packages for carp and 118# croak. They replace $CarpLevel, which is deprecated. The 119# $Max(EvalLen|(Arg(Len|Nums)) variables are used to specify how the eval 120# text and function arguments should be formatted when printed. 121 122# Comments added by Jos I. Boumans <kane@dwim.org> 11-Aug-2004 123# I can not get %CarpInternal or %Internal to work as advertised, 124# therefor leaving it out of the below documentation. 125# $CarpLevel may be decprecated according to the last comment, but 126# after 6 years, it's still around and in heavy use ;) 127 128=pod 129 130=head1 GLOBAL VARIABLES 131 132=head2 $Carp::CarpLevel 133 134This variable determines how many call frames are to be skipped when 135reporting where an error occurred on a call to one of C<Carp>'s 136functions. For example: 137 138 $Carp::CarpLevel = 1; 139 sub bar { .... or _error('Wrong input') } 140 sub _error { Carp::carp(@_) } 141 142This would make Carp report the error as coming from C<bar>'s caller, 143rather than from C<_error>'s caller, as it normally would. 144 145Defaults to C<0>. 146 147=head2 $Carp::MaxEvalLen 148 149This variable determines how many characters of a string-eval are to 150be shown in the output. Use a value of C<0> to show all text. 151 152Defaults to C<0>. 153 154=head2 $Carp::MaxArgLen 155 156This variable determines how many characters of each argument to a 157function to print. Use a value of C<0> to show the full length of the 158argument. 159 160Defaults to C<64>. 161 162=head2 $Carp::MaxArgNums 163 164This variable determines how many arguments to each function to show. 165Use a value of C<0> to show all arguments to a function call. 166 167Defaults to C<8>. 168 169=head2 $Carp::Verbose 170 171This variable makes C<Carp> use the C<longmess> function at all times. 172This effectively means that all calls to C<carp> become C<cluck> and 173all calls to C<croak> become C<confess>. 174 175Note, this is analogous to using C<use Carp 'verbose'>. 176 177Defaults to C<0>. 178 179=cut 180 181 182$CarpInternal{Carp}++; 183$CarpInternal{warnings}++; 184$CarpLevel = 0; # How many extra package levels to skip on carp. 185 # How many calls to skip on confess. 186 # Reconciling these notions is hard, use 187 # %Internal and %CarpInternal instead. 188$MaxEvalLen = 0; # How much eval '...text...' to show. 0 = all. 189$MaxArgLen = 64; # How much of each argument to print. 0 = all. 190$MaxArgNums = 8; # How many arguments to print. 0 = all. 191$Verbose = 0; # If true then make shortmess call longmess instead 192 193require Exporter; 194@ISA = ('Exporter'); 195@EXPORT = qw(confess croak carp); 196@EXPORT_OK = qw(cluck verbose longmess shortmess); 197@EXPORT_FAIL = qw(verbose); # hook to enable verbose mode 198 199=head1 BUGS 200 201The Carp routines don't handle exception objects currently. 202If called with a first argument that is a reference, they simply 203call die() or warn(), as appropriate. 204 205=cut 206 207# if the caller specifies verbose usage ("perl -MCarp=verbose script.pl") 208# then the following method will be called by the Exporter which knows 209# to do this thanks to @EXPORT_FAIL, above. $_[1] will contain the word 210# 'verbose'. 211 212sub export_fail { 213 shift; 214 $Verbose = shift if $_[0] eq 'verbose'; 215 return @_; 216} 217 218 219# longmess() crawls all the way up the stack reporting on all the function 220# calls made. The error string, $error, is originally constructed from the 221# arguments passed into longmess() via confess(), cluck() or shortmess(). 222# This gets appended with the stack trace messages which are generated for 223# each function call on the stack. 224 225sub longmess { 226 { 227 local($@, $!); 228 # XXX fix require to not clear $@ or $!? 229 # don't use require unless we need to (for Safe compartments) 230 require Carp::Heavy unless $INC{"Carp/Heavy.pm"}; 231 } 232 # Icky backwards compatibility wrapper. :-( 233 my $call_pack = caller(); 234 if ($Internal{$call_pack} or $CarpInternal{$call_pack}) { 235 return longmess_heavy(@_); 236 } 237 else { 238 local $CarpLevel = $CarpLevel + 1; 239 return longmess_heavy(@_); 240 } 241} 242 243 244# shortmess() is called by carp() and croak() to skip all the way up to 245# the top-level caller's package and report the error from there. confess() 246# and cluck() generate a full stack trace so they call longmess() to 247# generate that. In verbose mode shortmess() calls longmess() so 248# you always get a stack trace 249 250sub shortmess { # Short-circuit &longmess if called via multiple packages 251 { 252 local($@, $!); 253 # XXX fix require to not clear $@ or $!? 254 # don't use require unless we need to (for Safe compartments) 255 require Carp::Heavy unless $INC{"Carp/Heavy.pm"}; 256 } 257 # Icky backwards compatibility wrapper. :-( 258 my $call_pack = caller(); 259 local @CARP_NOT = caller(); 260 shortmess_heavy(@_); 261} 262 263 264# the following four functions call longmess() or shortmess() depending on 265# whether they should generate a full stack trace (confess() and cluck()) 266# or simply report the caller's package (croak() and carp()), respectively. 267# confess() and croak() die, carp() and cluck() warn. 268 269sub croak { die shortmess @_ } 270sub confess { die longmess @_ } 271sub carp { warn shortmess @_ } 272sub cluck { warn longmess @_ } 273 2741; 275