a question about header file! Under Microsoft visual C++: I add a head file which include all global variables. It can be compiled. But got a lot of link errors,such as: " 5-7.obj : error LNK2001: unresolved external symbol "class std::basic_ifstream<char,struct std::char_traits<char>; >;  fin" (?fin@@3V?$basic_ifstream@DU?$char_traits@D@std@@@std@@A) error LNK2001: unresolved external symbol "int *  Rxlev" (?Rxlev@@3PAHA) Debug/5_7.exe : fatal error LNK1120: 20 unresolved externals " My head file begin with: " #if !defined(DATA_PROCESS_H) #define DATA_PROCESS_H " and .cpp file begin with: " #include "dataprocess.h" " Who can help me? Thanks in advance! a question about header file! 連接錯就是你的符號沒有定義 如函數沒定義等 另外如果文件名是.cpp的話 編譯時不會說ifstream找不到的 還有就是標題寫清楚點 這樣可以寫成VC中鏈接出錯 a question about header file! --> Thanks 無雙 But I can't understand that if without head file(when I wrote all of varibles into .cpp file, it means 定義all of 函數), the program can be link and excuted. 標題寫清楚點? So how can I check it?How to modify it? sorry, I can't inpu chinese word. a question about header file! 你的帖子上有編輯 5-7.obj : error LNK2001: unresolved external symbol "class std::basic_ifstream<char,struct std::char_traits<char>; >; fin" (?fin@@3V?$basic_ifstream@DU?$char_traits@D@std@@@std@@A) 把文件名改成.cpp看 a question about header file! It is already a .cpp file. All of errors are here: 5-7.obj : error LNK2001: unresolved external symbol "class std::map<int,int,struct std::less<int>;,class std::allocator<int>; >;  order_map" (?order_map@@3V?$map@HHU?$less@H@std@@V?$allocator@H@2@@std@@A) 5-7.obj : error LNK2001: unresolved external symbol "bool  multiname_marker" (?multiname_marker@@3_NA) 5-7.obj : error LNK2001: unresolved external symbol "class std::set<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >;,struct std::less<class std::basic_string<char,struct std::char_traits<char>;,class std::alloca tor<char>; >; >;,class std::allocator<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >; >; >;  k_Calculation" (?k_Calculation@@3V?$set@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@U?$less@V?$basic_st ring@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@V?$allocator@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@@std@@A) 5-7.obj : error LNK2001: unresolved external symbol "class std::set<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >;,struct std::less<class std::basic_string<char,struct std::char_traits<char>;,class std::alloca tor<char>; >; >;,class std::allocator<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >; >; >;  k_Filters" (?k_Filters@@3V?$set@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@U?$less@V?$basic_string@DU? $char_traits@D@std@@V?$allocator@D@2@@std@@@2@V?$allocator@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@@std@@A) 5-7.obj : error LNK2001: unresolved external symbol "class std::set<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >;,struct std::less<class std::basic_string<char,struct std::char_traits<char>;,class std::alloca tor<char>; >; >;,class std::allocator<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >; >; >;  k_ColumnMapping" (?k_ColumnMapping@@3V?$set@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@U?$less@V?$basi c_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@V?$allocator@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@@std@@A) 5-7.obj : error LNK2001: unresolved external symbol "class std::set<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >;,struct std::less<class std::basic_string<char,struct std::char_traits<char>;,class std::alloca tor<char>; >; >;,class std::allocator<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >; >; >;  k_Common" (?k_Common@@3V?$set@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@U?$less@V?$basic_string@DU?$c har_traits@D@std@@V?$allocator@D@2@@std@@@2@V?$allocator@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@@std@@A) 5-7.obj : error LNK2001: unresolved external symbol "class std::multimap<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >;,class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >;, struct std::less<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >; >;,class std::allocator<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >; >; >;  c_Calculation" (?c_Calculati on@@3V?$multimap@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@V12@U?$less@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@V?$allocator@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@@std@@A) 5-7.obj : error LNK2001: unresolved external symbol "class std::multimap<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >;,class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >;, struct std::less<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >; >;,class std::allocator<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >; >; >;  c_Filters" (?c_Filters@@3V?$ multimap@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@V12@U?$less@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@V?$allocator@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@@std@@A) 5-7.obj : error LNK2001: unresolved external symbol "class std::multimap<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >;,class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >;, struct std::less<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >; >;,class std::allocator<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >; >; >;  c_ColumnMapping" (?c_ColumnM apping@@3V?$multimap@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@V12@U?$less@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@V?$allocator@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@@std@@A) 5-7.obj : error LNK2001: unresolved external symbol "class std::multimap<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >;,class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >;, struct std::less<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >; >;,class std::allocator<class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >; >; >;  c_Common" (?c_Common@@3V?$mu ltimap@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@V12@U?$less@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@V?$allocator@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@@std@@A) 5-7.obj : error LNK2001: unresolved external symbol "class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >;  val" (?val@@3V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@A) 5-7.obj : error LNK2001: unresolved external symbol "struct std::pair<class std::_Tree<class std::basic_string<char,struct $char_traits@D@std@@V?$allocator@ D@2@@std@@@2@@std@@V123@@std@@A) 5-7.obj : error LNK2001: unresolved external symbol "class std::basic_ifstream<char,struct std::char_traits<char>; >;  fin" (?fin@@3V?$basic_ifstream@DU?$char_traits@D@std@@@std@@A) 5-7.obj : error LNK2001: unresolved external symbol "class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >;  line_tmp" (?line_tmp@@3V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@A) 5-7.obj : error LNK2001: unresolved external symbol "int *  column" (?column@@3PAHA) 5-7.obj : error LNK2001: unresolved external symbol "class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >; *  k_element" (?k_element@@3PAV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@A) 5-7.obj : error LNK2001: unresolved external symbol "class std::basic_string<char,struct std::char_traits<char>;,class std::allocator<char>; >; *  key_element" (?key_element@@3PAV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@A) 5-7.obj : error LNK2001: unresolved external symbol "class std::basic_ofstream<char,struct std::char_traits<char>; >;  d_fout" (?d_fout@@3V?$basic_ofstream@DU?$char_traits@D@std@@@std@@A) 5-7.obj : error LNK2001: unresolved external symbol "char *  keyfield" (?keyfield@@3PADA) 5-7.obj : error LNK2001: unresolved external symbol "int *  Rxlev" (?Rxlev@@3PAHA) Debug/5_7.exe : fatal error LNK1120: 20 unresolved externals Error executing link.exe. 5_7.exe - 21 error(s), 0 warning(s) [ 關閉窗口 ]