رسالة خطأ..لم افهمها

السلام عليكم

ظهرت لي رسالة خطأ أثناء كتابة برنامج لم اعرف ما المشكلة الذي سبب الخطأ..

ارجوكم وضحوا لي ما هو الخطأ من خلال هذه الرسالة

و دمتم بحفظ الله

------ Build started: Project: sheet3, Configuration: Debug Win32 ------
Linking...
main.obj : error LNK2019: unresolved external symbol "public: __thiscall list<struct book,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >::~list<struct book,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >(void)" (??1?$list@Ubook@@V?$basic_string@DU?$char_traits@D@std@@V?$
allocator@D@2@@std@@@@QAE@XZ) referenced in function _main

main.obj : error LNK2019: unresolved external symbol "public: __thiscall list<struct book,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >::list<struct book,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >(void)" (??0?$list@Ubook@@V?$basic_string@DU?$char_traits@D@std@@V?
$allocator@D@2@@std@@@@QAE@XZ) referenced in function _main

C:\Documents and Settings\user\My Documents\Visual Studio 2008\Projects\sheet3\Debug\sheet3.exe : fatal error LNK1120: 2 unresolved externals
Build log was saved at "file://c:\Documents and Settings\user\My Documents\Visual Studio 2008\Projects\sheet3\sheet3\Debug\BuildLog.htm"
sheet3 - 3 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========