輸出時緩沖區(qū)疑惑

vinian

Mastering Perl 上的一個例子

1. 
   
2. #!/usr/bin/perl
   
3. use Devel::Size qw(size);
   
4. my $n;
   
5. print_message( "Before I do anything" );
   
6. print "Size is ", size( \$n );
   
7. print_message( "After I assign a string" );
   
8. $n = '1';
   
9. print "Size is ", size( \$n );
   
10. print_message( "After I use it as a number" );
    
11. my $m = $n + 1;
    
12. print "Size is ", size( \$n );
    
13. sub print_message { print "\n", "-" x 50, "\n$_[0]\n", "-" x 50, "\n" }
    

復制代碼

輸出：
--------------------------------------------------
Before I do anything
--------------------------------------------------
Size is 24
--------------------------------------------------
After I assign a string
--------------------------------------------------
Size is 56
--------------------------------------------------
After I use it as a number
--------------------------------------------------
Size is 64

因為好幾個地方都用到print_message,每次復制粘貼比較麻煩，就把它作成一個小的模塊

1. 
   
2. #Print.pm
   
3. package Print;
   
4. 
   
5. require     Exporter;
   
6. 
   
7. our @ISA            = qw(Exporter);
   
8. our @EXPORT         = qw(print_message);
   
9. our @EXPORT_OK      = qw();
   
10. our $VERSION        = 1.00;
    
11. 
    
12. sub print_message {
    
13.         print STDERR "\n", "-" x 50,
    
14.         "\n$_[0]\n", "-" x 50, "\n";
    
15. }
    
16. 
    
17. 1
    
18. 
    
19. #size.plx
    
20. #!/usr/bin/perl
    
21. 
    
22. use strict;
    
23. use warnings;
    
24. use Devel::Size qw/size/;
    
25. use Print;
    
26. 
    
27. my $n;
    
28. 
    
29. print_message("Before I do anything");
    
30. print "Size is ", size(\$n);
    
31. 
    
32. print_message("After I do something");
    
33. $n = '1';
    
34. print "Size is ", size(\$n);
    
35. 
    
36. print_message("After I do anything");
    
37. my $m = $n + 1;
    
38. print "Size is ", size(\$n);
    
39. 
    

復制代碼

輸出變成這樣了:
--------------------------------------------------
Before I do anything
--------------------------------------------------

--------------------------------------------------
After I do something
--------------------------------------------------

--------------------------------------------------
After I do anything
--------------------------------------------------
Size is 24Size is 56Size is 64

我的解決方法有兩個：
1. 在size.plx 文件開始設置 local $| = 1;
2. 在

1. print "Size is ", size(\$n);

復制代碼

后面添加換行符
即

1. print "Size is ", size(\$n), "\n";

復制代碼

但對第二個文件的錯誤輸出還是不太理解，請那位大俠解釋下，謝謝了

jason680

回復 1# vinian

你把print_message寫到模組時
變成 print STDERR ....
STDERR跟 STDOUT是不一樣的

vinian

回復  vinian

你把print_message寫到模組時
變成 print STDERR ....
STDERR跟 STDOUT是不一樣的
jason680 發(fā)表于 2010-11-14 23:01

謝了，一直就只盯著輸出，倒把這給忘檢查了...