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However, occasionally there is a need to disable warnings or strictness for some code that may look strange , but is actually correct. The -w switch cannot enable or disable particular warnings on particular ranges of code. When a particular warning or strict checking must be disabled, the no warnings or no strict pragmas should be used in as minimal a scope as possible. They should also disable the specific warning or strictness checker that would trigger a warning or fatal error , rather than disable all checks.
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| Code Block | ||||
|---|---|---|---|---|
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use warnings;
use strict;
my %days = ("Sunday" => 'pray',
"Monday" => 'work',
"Tuesday" => 'work',
"Wednesday" => 'work',
"Thursday" => 'work',
"Friday" => 'work',
"Saturday" => 'rest');
sub what_to_do {
my $day = shift;
if ($days{$day} eq 'work') {
return 'work hard';
}
if (exists $days{$day}) {
return $days{$day};
} else {
return "do nothing";
}
}
my $task = what_to_do('tomorrow');
print "Prepare to $task\n";
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This code produces the output:
| Code Block |
|---|
Use of uninitialized value within %days in string eq at ./example.pl line 16.
Prepare to do nothing
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| Code Block | ||||
|---|---|---|---|---|
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use warnings;
use strict;
no warnings 'uninitialized';
my %days = ("Sunday" => 'pray',
# ...
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Unfortunately while , although this does code correctly suppress suppresses the warning message, it has the undesired effect of suppressing the warning message throughout the entire program . This has the likely effect of suppressing and will likely suppress the warning in other lines of code that are not known to be correct.
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| Code Block | ||||
|---|---|---|---|---|
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sub what_to_do {
my $day = shift;
no warnings 'uninitialized';
if ($days{$day} eq 'work') {
return 'work hard';
}
if (exists $days{$day}) {
return $days{$day};
} else {
return "do nothing";
}
}
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| Code Block | ||||
|---|---|---|---|---|
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use strict;
use warnings;
our $sunday = 'pray';
our $monday = 'work';
our $tuesday = 'work';
our $wednesday = 'work';
our $thursday = 'work';
our $friday = 'work';
our $saturday = 'rest';
sub what_to_do {
my $day = shift;
no warnings 'uninitialized';
if ($$day eq 'work') {
return 'work hard';
}
if (defined $$day) {
return $$day;
} else {
return "do nothing";
}
}
my $task = what_to_do('tomorrow');
print "Prepare to $task\n";
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The strict pragma catches the improper reference and aborts the program, producing the following error message:
| Code Block |
|---|
Can't use string ("tomorrow") as a SCALAR ref while "strict refs" in use at ./example.pl line 19.
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This noncompliant code example disables the strict pragma, thus producing proper output. However, strict-ness strictness is suppressed throughout the entire program.
| Code Block | ||||
|---|---|---|---|---|
| ||||
use warnings;
use strict;
no strict 'refs';
our $sunday = 'pray';
# ...
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This code produces the output:
| Code Block |
|---|
Prepare to do nothing
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This example may be considered correct, but the code works by referencing a nonexistent variable $tomorrow.
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This compliant solution suppresses the strict-ness strictness checking to as minimal a scope as possible. Because the strict checking is suppressed only inside the what_to_do subroutine, other regions of the code can still be checked for strict compliance.
| Code Block | ||||
|---|---|---|---|---|
| ||||
sub what_to_do {
my $day = shift;
no warnings 'uninitialized';
no strict 'refs';
if ($$day eq 'work') {
return 'work hard';
}
if (defined $$day) {
return $$day;
} else {
return "do nothing";
}
}
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