哈希的典型应用

2011-02-09 wcdj

 

(1) exists函数
(2) delete函数
(3) 哈希值内插
(4) %ENV哈希
3道应用题目

(1) exists函数
用于检查哈希中是否有某个键。它能返回真或假，分别表示键存在与否，和键对应的值无关。
print "exists函数/n";my %my_hash = ( "wcdj"=>"C++","gerry"=>"Perl","yj"=>"Python" );print "each函数/n";while ( ($key, $value) = each %my_hash ) {print "$key => $value/n";}print "检查哈希中是否有某个键/n";if (exists $my_hash{"gerry"}) {print "have/n";# 输出此句} else {print "not have/n";}if (exists $my_hash{"none"}) {print "have/n";} else {print "not have/n";# 输出此句}

 

(2) delete函数
用于从哈希中删除指定的键和其相对应的值。假如没有这样的键，它就会直接结束，而不会出现任何警告或错误信息。

print "exists函数/n";my %my_hash = ( "wcdj"=>"C++","gerry"=>"Perl","yj"=>"Python" );print "each函数/n";while ( ($key, $value) = each %my_hash ) {print "$key => $value/n";}print "检查哈希中是否有某个键/n";if (exists $my_hash{"gerry"}) {print "have/n";# 输出此句} else {print "not have/n";}print "delete函数/n";my $person = "gerry";delete $my_hash{$person};# 删除$person的信息if (exists $my_hash{"gerry"}) {print "have/n";} else {print "not have/n";# 输出此句}

 

注意：执行delete之后，并不是将undef存入哈希值。在delete之后，键便不会出现在哈希之中，但是存入undef之后，键却一定会存在。

(3) 哈希值内插
注意：可以将单一哈希元素内插到双引号引起的字符串中。但是整个哈希的内插是不支持的。

(4) %ENV哈希

print "%ENV哈希/n";print "PATH is $ENV{PATH}/n";# 根据系统的设定输出如下%ENV哈希PATH is /usr/local/bin:/usr/bin:/bin:/usr/X11R6/bin:/cygdrive/c/Perl/site/bin:/cygdrive/c/Perl/bin:/cygdrive/c/Python26/Scripts:/cygdrive/c/Python26/:/cygdrive/c/Tcl/bin:/cygdrive/c/WINDOWS/system32:/cygdrive/c/WINDOWS:/cygdrive/c/WINDOWS/System32/Wbem:/cygdrive/c/Program Files/Microsoft SQL Server/90/Tools/binn/:/cygdrive/c/Python25:/cygdrive/d/Program Files/Vim:%APPDATA%/Python/Scripts:/cygdrive/c/Program Files/Microsoft Visual Studio/Common/Tools/WinNT:/cygdrive/c/Program Files/Microsoft Visual Studio/Common/MSDev98/Bin:/cygdrive/c/Program Files/Microsoft Visual Studio/Common/Tools:/cygdrive/c/Program Files/Microsoft Visual Studio/VC98/bin:/home/WCDJ/ns-allinone-2.27/bin:/home/WCDJ/ns-allinone-2.27/tcl8.4.5/unix:/home/WCDJ/ns-allinone-2.27/tk8.4.5/unix

 

【应用1】
编程读入用户指定的名字并且汇报相应的姓。
my %last_name_hash = ( "Jia"=>"Yang","Ming"=>"Li","San"=>"Zhang" );print "Please enter a first name: ";# 输入名chomp(my $name=<STDIN>);# 检查次键是否存在if (exists $last_name_hash{$name}) {#print "have/n"; print "That's $name $last_name_hash{$name}"; } else {print "not have/n";}

 

【应用2】
编程读取一系列单词，每行一个直到文件结束，然后打印每个单词出现次数的列表。

my(@words, %count, $word);# 声明变量(可以省略)chomp(@words=<STDIN>);# UNIX下，按Ctrl-D结束输入# 记录foreach $word (@words) {$count{$word} += 1;}# 输出foreach $word (sort keys %count) {print "$word was seen $count{$word} times./n";}

 

【应用3】
编程输出%ENV哈希所有的键/值对，输出按照ASCII编码排序，分两列打印（让打印结果纵向对齐）。

my $longest=0;# 记录最长的字符串foreach my $key (keys %ENV) {my $key_length=length($key);$longest=$key_length if $key_length>$longest;}# 输出foreach my $key (sort keys %ENV) {printf "%-${longest}s %s/n", $key, $ENV{$key};# 向左对齐}

输出：

!C: C:/Documents and Settings/WCDJ/桌面!G: G:/CrossPlatform/ns2_tcl/LEACH/Do_Myself/binALLUSERSPROFILE C:/Documents and Settings/All UsersAPPDATA C:/Documents and Settings/WCDJ/Application DataCLIENTNAME ConsoleCOLINUX C:/coLinuxCOMMONPROGRAMFILES C:/Program Files/Common FilesCOMPUTERNAME WCDJ_PCCOMSPEC C:/WINDOWS/system32/cmd.exeCVS_RSH /bin/sshDEFLOGDIR C:/Documents and Settings/All Users/Application Data/McAfee/DesktopProtectionFP_NO_HOST_CHECK NOHOME /home/WCDJHOMEDRIVE C:HOMEPATH /Documents and Settings/WCDJHOSTNAME WCDJ_PCINCLUDE C:/Program Files/Microsoft Visual Studio/VC98/atl/include;C:/Program Files/Microsoft Visual Studio/VC98/mfc/include;C:/Program Files/Microsoft Visual Studio/VC98/includeINFOPATH /usr/local/info:/usr/info:/usr/share/info:/usr/autotool/devel/info:/usr/autotool/stable/info:LANG zh_CNLD_LIBRARY_PATH /home/WCDJ/ns-allinone-2.27/otcl-1.8:/home/WCDJ/ns-allinone-2.27/lib:/usr/X11R6/lib:/usr/local/libLIB C:/Program Files/Microsoft Visual Studio/VC98/mfc/lib;C:/Program Files/Microsoft Visual Studio/VC98/libLOGONSERVER //WCDJ_PCMAKE_MODE unixMANPATH /usr/local/man:/usr/man:/usr/share/man:/usr/autotool/devel/man::/usr/ssl/manMSDEVDIR C:/Program Files/Microsoft Visual Studio/Common/MSDev98NUMBER_OF_PROCESSORS 2OLDPWD /home/WCDJOS Windows_NTPATH /usr/local/bin:/usr/bin:/bin:/usr/X11R6/bin:/cygdrive/c/Perl/site/bin:/cygdrive/c/Perl/bin:/cygdrive/c/Python26/Scripts:/cygdrive/c/Python26/:/cygdrive/c/Tcl/bin:/cygdrive/c/WINDOWS/system32:/cygdrive/c/WINDOWS:/cygdrive/c/WINDOWS/System32/Wbem:/cygdrive/c/Program Files/Microsoft SQL Server/90/Tools/binn/:/cygdrive/c/Python25:/cygdrive/d/Program Files/Vim:%APPDATA%/Python/Scripts:/cygdrive/c/Program Files/Microsoft Visual Studio/Common/Tools/WinNT:/cygdrive/c/Program Files/Microsoft Visual Studio/Common/MSDev98/Bin:/cygdrive/c/Program Files/Microsoft Visual Studio/Common/Tools:/cygdrive/c/Program Files/Microsoft Visual Studio/VC98/bin:/home/WCDJ/ns-allinone-2.27/bin:/home/WCDJ/ns-allinone-2.27/tcl8.4.5/unix:/home/WCDJ/ns-allinone-2.27/tk8.4.5/unixPATHEXT .COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.tcl;.py;.pywPKG_CONFIG_PATH :/usr/X11R6/lib/pkgconfigPROCESSOR_ARCHITECTURE x86PROCESSOR_IDENTIFIER x86 Family 6 Model 15 Stepping 13, GenuineIntelPROCESSOR_LEVEL 6PROCESSOR_REVISION 0f0dPROGRAMFILES C:/Program FilesPROMPT $P$GPS1 /[/033]0;/w/007/033[32m/]/u@/h /[/033[33m/w/033[0m/]$ PWD /home/WCDJ/perl_testRCA_LIBRARY /home/WCDJ/ns-allinone-2.27/ns-2.27/mit/rcaSESSIONNAME ConsoleSHLVL 1SYSTEMDRIVE C:SYSTEMROOT C:/WINDOWSTCL_LIBRARY /home/WCDJ/ns-allinone-2.27/tcl8.4.5/library:/usr/libTEMP /cygdrive/c/DOCUME~1/WCDJ/LOCALS~1/TempTERM cygwinTMP /cygdrive/c/DOCUME~1/WCDJ/LOCALS~1/TempUSER WCDJUSERDOMAIN WCDJ_PCUSERNAME WCDJUSERPROFILE C:/Documents and Settings/WCDJVS90COMNTOOLS C:/Program Files/Microsoft Visual Studio 9.0/Common7/Tools/VSEDEFLOGDIR C:/Documents and Settings/All Users/Application Data/McAfee/DesktopProtectionWINDIR C:/WINDOWS_ ./hashuAMPS_LIBRARY /home/WCDJ/ns-allinone-2.27/ns-2.27/mit/uAMPS