usUselesse of addition (+) in void context at ./16.pl line 7.
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如果在perl中你定义了一个子程序,并且启用了警告,子程序中的运算结果没有被存储起来,这时候perl会将其丢弃,并且报错:Useless use of addition (+) in void context at来警告你,其中的void context(空的上下文),表示运算结果没有存储到变量里,也未被任何函数使用。
例子:
[root@mysql1 perl]# cat 16.pl
#!/usr/bin/env perl
use warnings FATAL => 'all';
sub sum_of_barney_and_fred {
print "hey, you called the sum_of_barney_and_fred subroutine!\n";
$fred + $barney;
print "hey, i'm returning a value now!\n";
}
$fred = 3;
$barney = 4;
$wilma = &sum_of_barney_and_fred;
print "\$wilma is $wilma.\n";
$betty = 3 * &sum_of_barney_and_fred;
print "\$betty is $betty.\n";
[root@mysql1 perl]# ./16.pl
usUselesse of addition (+) in void context at ./16.pl line 7.
解决方法有两个:
1.禁用告警,就是注释#use warnings FATAL => 'all';
2.去掉子程序的最后的print,这样的话返回值就是两个变量的加的结果了,会被引用,就不会报错了。
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