如何判断一个变量在 Perl 中是否有数值? [英] How do I tell if a variable has a numeric value in Perl?

问题描述

在 Perl 中是否有一种简单的方法可以让我确定给定变量是否为数字?大致如下:

Is there a simple way in Perl that will allow me to determine if a given variable is numeric? Something along the lines of:

if (is_number($x))
{ ... }

将是理想的.在使用 -w 开关时不会引发警告的技术当然是首选.

would be ideal. A technique that won't throw warnings when the -w switch is being used is certainly preferred.

推荐答案

使用 Scalar::Util::looks_like_number() 使用内部 Perl C API 的looks_like_number() 函数，这可能是最有效的方法来做到这一点.请注意，字符串inf"和infinity"被视为数字.

Use Scalar::Util::looks_like_number() which uses the internal Perl C API's looks_like_number() function, which is probably the most efficient way to do this. Note that the strings "inf" and "infinity" are treated as numbers.

#!/usr/bin/perl

use warnings;
use strict;

use Scalar::Util qw(looks_like_number);

my @exprs = qw(1 5.25 0.001 1.3e8 foo bar 1dd inf infinity);

foreach my $expr (@exprs) {
    print "$expr is", looks_like_number($expr) ? '' : ' not', " a number
";
}

给出这个输出:

1 is a number
5.25 is a number
0.001 is a number
1.3e8 is a number
foo is not a number
bar is not a number
1dd is not a number
inf is a number
infinity is a number

另见:

• perldoc Scalar::Util
• perldoc perlapi for looks_like_number

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