“printf中的冗余参数”警告
为什么我在 Perl 中收到此错误“printf 中的冗余参数”？这表示格式字符串需要的值多于包含的值。我提供的格式字符串是否正确？
输入文件：
<?xml version='1.0'?>
<playlist>
<movie>
<title>Apollo 13</title>
<director>Ron Howard</director>
<release-date>1995-06-30</release-date>
<mpaa-rating>PG</mpaa-rating>
<running-time>140</running-time>
<genre>adventure</genre>
<genre>drama</genre>
<cast>
<person name="Tom Hanks" role="Jim Lovell" />
<person name="Bill Paxton" role="Fred Haise" />
<person name="Kevin Bacon" role="Jack Swigert" />
<person name="Gary Sinise" role="Ken Mattingly" />
<person name="Ed Harris" role="Gene Kranz" />
</cast>
<imdb-info url="http://www.imdb.com/title/tt0112384/">
<synopsis>
NASA must devise a strategy to return Apollo 13 to Earth safely
after the spacecraft undergoes massive internal damage putting
the lives of the three astronauts on board in jeopardy.
</synopsis>
<score>7.6</score>
</imdb-info>
</movie>
<movie>
<title>Solaris</title>
<director>Steven Soderbergh</director>
<release-date>2002-11-27</release-date>
<mpaa-rating>PG-13</mpaa-rating>
<running-time>99</running-time>
<genre>drama</genre>
<genre>mystery</genre>
<genre>romance</genre>
<cast>
<person name="George Clooney" role="Chris Kelvin" />
<person name="Natascha McElhone" role="Rheya" />
<person name="Ulrich Tukur" role="Gibarian" />
</cast>
<imdb-info url="http://www.imdb.com/title/tt0307479/">
<synopsis>
A troubled psychologist is sent to investigate the crew of an
isolated research station orbiting a bizarre planet.
</synopsis>
<score>6.2</score>
</imdb-info>
</movie>
</playlist>
我的代码：
use warnings;
use XML::LibXML;
my $filename = 'playlist.xml';
my $dom = XML::LibXML->load_xml(location => $filename);
printf("%-20s %-35s %-10s %-10sn", "Title: ", "Director: ", "Rating: ", "Duration: ");
foreach my $movie ($dom->findnodes('//movie')) {
printf("%-20s %-35s %-10s %-10sn", # <-- This is line 7
$movie->findvalue('./title'),
$movie->findvalue('./director'),
$movie->findvalue('./mpaa-rating'),
$movie->findvalue('./running-time'),
" minutes");
}
预期输出：
Title: Director: Rating: Duration:
Apollo 13 Ron Howard PG 140
Solaris Steven Soderbergh PG-13 99
Ender's Game Gavin Hood PG-13 114
Interstellar Christopher Nolan PG-13 169
The Martian Ridley Scott PG-13 144
获取输出：
Title: Director: Rating: Duration:
Redundant argument in printf at movie.pl line 7.
Apollo 13 Ron Howard PG 140
Redundant argument in printf at movie.pl line 7.
Solaris Steven Soderbergh PG-13 99
Redundant argument in printf at movie.pl line 7.
Ender's Game Gavin Hood PG-13 114
Redundant argument in printf at movie.pl line 7.
Interstellar Christopher Nolan PG-13 169
.
.
.
为什么 Perl 会这样？
回答
这printf：
printf("%-20s %-35s %-10s %-10sn",
$movie->findvalue('./title'),
$movie->findvalue('./director'),
$movie->findvalue('./mpaa-rating'),
$movie->findvalue('./running-time'),
" minutes");
需要 4 个参数，因为它包含 4 %<something>。但是，您提供了 5 个参数。您可以minutes输入格式字符串（并将其从参数中删除）：
printf("%-20s %-35s %-10s %-10s minutesn",
$movie->findvalue('./title'),
$movie->findvalue('./director'),
$movie->findvalue('./mpaa-rating'),
$movie->findvalue('./running-time'));
或者，如果您想minutes紧挨着分钟数，请将其连接到$movie->findvalue('./running-time')：
printf("%-20s %-35s %-10s %-10sn",
$movie->findvalue('./title'),
$movie->findvalue('./director'),
$movie->findvalue('./mpaa-rating'),
$movie->findvalue('./running-time') . " minutes");
可能让您感到困惑的是，它print需要一个参数列表来打印，而printf需要一个格式字符串和一个参数列表来替换和格式化格式字符串。这样做就好了：
print($movie->findvalue('./title'),
$movie->findvalue('./director'),
$movie->findvalue('./mpaa-rating'),
$movie->findvalue('./running-time'),
" minutesn");
（尽管这不会按照您的意愿格式化输出）