VC下 Runtime 版本不同原因引起的一個編譯問題案例
Background
MSDN中對於在不同的配置下Link的LIB作了說明：
C Runtime Library：
|
開關 |
對應的庫 |
版本 |
|
/MD |
MSVCRT.LIB |
多執行緒DLL的Release版本 |
|
/MDd |
MSVCRTD.LIB |
多執行緒DLL的Debug版本 |
|
/MT |
LIBCMT.LIB |
多執行緒靜態連結的Release版本 |
|
/MTd |
LIBCMTD.LIB |
多執行緒靜態連結的Debug版本 |
|
/clr |
MSVCMRT.LIB |
託管程式碼和非託管程式碼混合 |
|
/clr:pure |
MSVCURT.LIB |
純託管程式碼 |
C++ Standard Library：
|
開關 |
對應的庫 |
版本 |
|
/MD |
MSVCPRT.LIB |
多執行緒DLL的Release版本 |
|
/MDd |
MSVCPRTD.LIB |
多執行緒DLL的Debug版本 |
|
/MT |
LIBCPMT.LIB |
多執行緒靜態連結的Release版本 |
|
/MTd |
LIBCPMTD.LIB |
多執行緒靜態連結的Debug版本 |
編譯器會自動根據編譯選項，選擇對應的LIB檔案。一般情況下這不會出現問題。
然而，在部分情況下，一旦你的程式的各個部分（LIB, OBJ…）並非由相同的編譯選項編譯出，而Link在一起的話，會出現各種各樣的看似很難解決的問題，這類問題主要以重複定義的錯誤形式存在，通常的解決方法也很簡單，就是選擇同樣的編譯選項進行編譯之後再Link。
Case Study
之前剛下載了ANTLR，在準備編譯它的Example的時候發現了下面的Build錯誤（我自己為這個例子建立了VS的專案，當前配置為動態連結Runtime庫，Debug版）：
|
1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: __thiscall std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >::~basic_string<char,struct std::char_traits<char>,class std::allocator<char> >(void)" (??1?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@QAE@XZ) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > & __thiscall std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >::replace(unsigned int,unsigned int,char const *,unsigned int)" (?replace@?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@QAEAAV12@IIPBDI@Z) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: void __thiscall std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >::reserve(unsigned int)" (?reserve@?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@QAEXI@Z) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: unsigned int __thiscall std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >::length(void)const " (?length@?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@QBEIXZ) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > & __thiscall std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >::operator+=(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &)" (??Y?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@QAEAAV01@ABV01@@Z) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: __thiscall std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &)" (??0?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@QAE@ABV01@@Z) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: char const & __thiscall std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >::operator[](unsigned int)const " (??A?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@QBEABDI@Z) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > & __thiscall std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >::operator=(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &)" (??4?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@QAEAAV01@ABV01@@Z) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > & __thiscall std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >::operator=(char const *)" (??4?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@QAEAAV01@PBD@Z) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: __thiscall std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >(char const *)" (??0?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@QAE@PBD@Z) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > __cdecl std::operator+<char,struct std::char_traits<char>,class std::allocator<char> >(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &)" (??$?HDU?$char_traits@D@std@@V?$allocator@D@1@@std@@YA?AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@0@ABV10@0@Z) already defined in antlr.lib(MismatchedCharException.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: char const * __thiscall std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >::c_str(void)const " (?c_str@?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@QBEPBDXZ) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "bool __cdecl std::operator<<char,struct std::char_traits<char>,class std::allocator<char> >(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &)" (??$?MDU?$char_traits@D@std@@V?$allocator@D@1@@std@@YA_NABV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@0@0@Z) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: class std::basic_ostream<char,struct std::char_traits<char> > & __thiscall std::basic_ostream<char,struct std::char_traits<char> >::operator<<(class std::basic_ostream<char,struct std::char_traits<char> > & (__cdecl*)(class std::basic_ostream<char,struct std::char_traits<char> > &))" (??6?$basic_ostream@DU?$char_traits@D@std@@@std@@QAEAAV01@P6AAAV01@AAV01@@Z@Z) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: class std::basic_ostream<char,struct std::char_traits<char> > & __thiscall std::basic_ostream<char,struct std::char_traits<char> >::operator<<(int)" (??6?$basic_ostream@DU?$char_traits@D@std@@@std@@QAEAAV01@H@Z) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "class std::basic_ostream<char,struct std::char_traits<char> > & __cdecl std::endl(class std::basic_ostream<char,struct std::char_traits<char> > &)" (?endl@std@@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@1@AAV21@@Z) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: void __thiscall std::basic_ios<char,struct std::char_traits<char> >::setstate(int,bool)" (?setstate@?$basic_ios@DU?$char_traits@D@std@@@std@@QAEXH_N@Z) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: int __thiscall std::ios_base::width(int)" (?width@ios_base@std@@QAEHH@Z) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: int __thiscall std::basic_streambuf<char,struct std::char_traits<char> >::sputn(char const *,int)" (?sputn@?$basic_streambuf@DU?$char_traits@D@std@@@std@@QAEHPBDH@Z) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: static bool __cdecl std::char_traits<char>::eq_int_type(int const &,int const &)" (?eq_int_type@?$char_traits@D@std@@SA_NABH0@Z) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: static int __cdecl std::char_traits<char>::eof(void)" (?eof@?$char_traits@D@std@@SAHXZ) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: int __thiscall std::basic_streambuf<char,struct std::char_traits<char> >::sputc(char)" (?sputc@?$basic_streambuf@DU?$char_traits@D@std@@@std@@QAEHD@Z) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: class std::basic_streambuf<char,struct std::char_traits<char> > * __thiscall std::basic_ios<char,struct std::char_traits<char> >::rdbuf(void)const " (?rdbuf@?$basic_ios@DU?$char_traits@D@std@@@std@@QBEPAV?$basic_streambuf@DU?$char_traits@D@std@@@2@XZ) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: char __thiscall std::basic_ios<char,struct std::char_traits<char> >::fill(void)const " (?fill@?$basic_ios@DU?$char_traits@D@std@@@std@@QBEDXZ) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: int __thiscall std::ios_base::flags(void)const " (?flags@ios_base@std@@QBEHXZ) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: int __thiscall std::ios_base::width(void)const " (?width@ios_base@std@@QBEHXZ) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: static unsigned int __cdecl std::char_traits<char>::length(char const *)" (?length@?$char_traits@D@std@@SAIPBD@Z) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: class std::basic_ostream<char,struct std::char_traits<char> > & __thiscall std::basic_ostream<char,struct std::char_traits<char> >::flush(void)" (?flush@?$basic_ostream@DU?$char_traits@D@std@@@std@@QAEAAV12@XZ) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: class std::basic_ostream<char,struct std::char_traits<char> > * __thiscall std::basic_ios<char,struct std::char_traits<char> >::tie(void)const " (?tie@?$basic_ios@DU?$char_traits@D@std@@@std@@QBEPAV?$basic_ostream@DU?$char_traits@D@std@@@2@XZ) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: bool __thiscall std::ios_base::good(void)const " (?good@ios_base@std@@QBE_NXZ) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: void __thiscall std::basic_ostream<char,struct std::char_traits<char> >::_Osfx(void)" (?_Osfx@?$basic_ostream@DU?$char_traits@D@std@@@std@@QAEXXZ) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: void __thiscall std::basic_streambuf<char,struct std::char_traits<char> >::_Lock(void)" (?_Lock@?$basic_streambuf@DU?$char_traits@D@std@@@std@@QAEXXZ) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "public: void __thiscall std::basic_streambuf<char,struct std::char_traits<char> >::_Unlock(void)" (?_Unlock@?$basic_streambuf@DU?$char_traits@D@std@@@std@@QAEXXZ) already defined in antlr.lib(CharScanner.obj) 1>msvcprtd.lib(MSVCP80D.dll) : error LNK2005: "class std::basic_ostream<char,struct std::char_traits<char> > & __cdecl std::operator<<<char,struct std::char_traits<char>,class std::allocator<char> >(class std::basic_ostream<char,struct std::char_traits<char> > &,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &)" (??$?6DU?$char_traits@D@std@@V?$allocator@D@1@@std@@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@0@AAV10@ABV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@0@@Z) already defined in antlr.lib(LLkParser.obj) 1>libcpmt.lib(locale0.obj) : error LNK2005: "private: static class std::locale::_Locimp * __cdecl std::locale::_Getgloballocale(void)" (?_Getgloballocale@locale@std@@CAPAV_Locimp@12@XZ) already defined in msvcprtd.lib(MSVCP80D.dll) 1>libcpmt.lib(locale0.obj) : error LNK2005: "private: static void __cdecl std::locale::facet::facet_Register(class std::locale::facet *)" (?facet_Register@facet@locale@std@@CAXPAV123@@Z) already defined in msvcprtd.lib(MSVCP80D.dll) 1>libcpmt.lib(locale0.obj) : error LNK2005: "public: static void __cdecl std::_Locinfo::_Locinfo_dtor(class std::_Locinfo *)" (?_Locinfo_dtor@_Locinfo@std@@SAXPAV12@@Z) already defined in msvcprtd.lib(MSVCP80D.dll) 1>libcpmt.lib(locale0.obj) : error LNK2005: "public: static void __cdecl std::_Locinfo::_Locinfo_ctor(class std::_Locinfo *,char const *)" (?_Locinfo_ctor@_Locinfo@std@@SAXPAV12@PBD@Z) already defined in msvcprtd.lib(MSVCP80D.dll) 1>libcpmt.lib(xmutex.obj) : error LNK2005: "public: void __thiscall std::_Mutex::_Lock(void)" (?_Lock@_Mutex@std@@QAEXXZ) already defined in msvcprtd.lib(MSVCP80D.dll) 1>libcpmt.lib(xmutex.obj) : error LNK2005: "public: void __thiscall std::_Mutex::_Unlock(void)" (?_Unlock@_Mutex@std@@QAEXXZ) already defined in msvcprtd.lib(MSVCP80D.dll) 1>libcpmt.lib(xlock.obj) : error LNK2005: "public: __thiscall std::_Lockit::_Lockit(int)" (??0_Lockit@std@@QAE@H@Z) already defined in msvcprtd.lib(MSVCP80D.dll) 1>libcpmt.lib(xlock.obj) : error LNK2005: "public: __thiscall std::_Lockit::~_Lockit(void)" (??1_Lockit@std@@QAE@XZ) already defined in msvcprtd.lib(MSVCP80D.dll) 1>LIBCMT.lib(invarg.obj) : error LNK2005: __invoke_watson already defined in MSVCRTD.lib(MSVCR80D.dll) 1>LIBCMT.lib(invarg.obj) : error LNK2005: __invalid_parameter already defined in MSVCRTD.lib(MSVCR80D.dll) 1>LIBCMT.lib(setlocal.obj) : error LNK2005: __configthreadlocale already defined in MSVCRTD.lib(MSVCR80D.dll) 1>LIBCMT.lib(tidtable.obj) : error LNK2005: __encode_pointer already defined in MSVCRTD.lib(MSVCR80D.dll) 1>LIBCMT.lib(tidtable.obj) : error LNK2005: __decode_pointer already defined in MSVCRTD.lib(MSVCR80D.dll) 1>LIBCMT.lib(tolower.obj) : error LNK2005: _tolower already defined in MSVCRTD.lib(MSVCR80D.dll) 1>LIBCMT.lib(crt0dat.obj) : error LNK2005: __amsg_exit already defined in MSVCRTD.lib(MSVCR80D.dll) 1>LIBCMT.lib(crt0dat.obj) : error LNK2005: __initterm_e already defined in MSVCRTD.lib(MSVCR80D.dll) 1>LIBCMT.lib(crt0dat.obj) : error LNK2005: _exit already defined in MSVCRTD.lib(MSVCR80D.dll) 1>LIBCMT.lib(crt0dat.obj) : error LNK2005: __exit already defined in MSVCRTD.lib(MSVCR80D.dll) 1>LIBCMT.lib(crt0dat.obj) : error LNK2005: __cexit already defined in MSVCRTD.lib(MSVCR80D.dll) 1>LIBCMT.lib(lconv.obj) : error LNK2005: _localeconv already defined in MSVCRTD.lib(MSVCR80D.dll) 1>LIBCMT.lib(mlock.obj) : error LNK2005: __unlock already defined in MSVCRTD.lib(MSVCR80D.dll) 1>LIBCMT.lib(mlock.obj) : error LNK2005: __lock already defined in MSVCRTD.lib(MSVCR80D.dll) 1>LIBCMT.lib(winxfltr.obj) : error LNK2005: __XcptFilter already defined in MSVCRTD.lib(MSVCR80D.dll) 1>LIBCMT.lib(crt0init.obj) : error LNK2005: ___xi_a already defined in MSVCRTD.lib(cinitexe.obj) 1>LIBCMT.lib(crt0init.obj) : error LNK2005: ___xi_z already defined in MSVCRTD.lib(cinitexe.obj) 1>LIBCMT.lib(crt0init.obj) : error LNK2005: ___xc_a already defined in MSVCRTD.lib(cinitexe.obj) 1>LIBCMT.lib(crt0init.obj) : error LNK2005: ___xc_z already defined in MSVCRTD.lib(cinitexe.obj) 1>LIBCMT.lib(hooks.obj) : error LNK2005: "void __cdecl terminate(void)" (?terminate@@YAXXZ) already defined in MSVCRTD.lib(MSVCR80D.dll) 1>LIBCMT.lib(crt0.obj) : error LNK2005: _mainCRTStartup already defined in MSVCRTD.lib(crtexe.obj) 1>LIBCMT.lib(errmode.obj) : error LNK2005: ___set_app_type already defined in MSVCRTD.lib(MSVCR80D.dll) 1>LIBCMT.lib(_ctype.obj) : error LNK2005: _isprint already defined in MSVCRTD.lib(MSVCR80D.dll) 1>MSVCRTD.lib(MSVCR80D.dll) : error LNK2005: __stricmp already defined in LIBCMT.lib(stricmp.obj) 1>LINK : warning LNK4098: defaultlib 'MSVCRTD' conflicts with use of other libs; use /NODEFAULTLIB:library 1>LINK : warning LNK4098: defaultlib 'LIBCMT' conflicts with use of other libs; use /NODEFAULTLIB:library 1>D:/home/doc/Visual Studio 2005/Projects/tst_antlr_3/Debug/tst_antlr_3.exe : fatal error LNK1169: one or more multiply defined symbols found |
分析一下錯誤來源，會發現：
1. 錯誤來源主要是重複定義的問題，而且重複定義的基本上都是VC Runtime和Standard C++ Library中的函式
2. LIBCMT和LIBCPMT為Release下的Lib，本來不應該出現在Debug版本的連結的Lib中
3. 重複定義的問題主要出現在：LIBCMT, LIBCPMT, MSVCPRTD, MSVCRTD
來看看出問題的LIB是那些：
1. LIBCMT：C Runtime庫的多執行緒靜態連結的Release版本
2. LIBCPMT：C++ Standard Library的多執行緒靜態連結的Release版本
3. MSVCPRTD：C++ Standard Library的多執行緒DLL的Debug版本
4. MSVCRTD：C Runtime Library的多執行緒DLL的Debug版本
當前我們的配置是多執行緒DLL的Debug版，因此3和4是應該出現在link的列表中的，不屬於多餘。而後兩者則是隻是當多執行緒靜態連結Release版中才會出現。這提示我在專案中加入的ANTLR.LIB可能是造成這個問題的根源，因為靜態庫的編譯選項很容易和主程式發生衝突，並且根據實際資訊我們可以看出ANTLR.LIB應該是用多執行緒靜態連結的Release版本來編譯的。
這樣，解決方法就很清楚了：
1. 切換到Release，因為ANTLR.LIB是在Release下面編譯的
2. 把Run Time庫的版本修改成多執行緒靜態連結
做了這兩個修改之後編譯通過。
還有一種方法是，自己用多執行緒DLL的Debug版重新編譯一次ANTLR，生成一個新的ANTLRD.LIB，再link這個Lib也可以解決這個問題。
Summary
1. 知道各個不同的LIB代表的版本資訊非常重要，可以幫助快速定位問題
2. 在程式設計的時候，一定要把所有的專案的編譯選項（是靜態連結Runtime庫還是動態連結Runtime庫，Debug/Release）配置成一樣的。如果部分LIB/OBJ是由第三方提供（OBJ情況很少見），一般情況下只能調整自己的編譯選項，除非你可以要求第三方提供其他版本的編譯好的LIB
3. 在釋出可重用的靜態LIB庫供其他人呼叫的時候，最好對應不同的編譯選項，乃至VC版本，提供不同版本的LIB。VC自己的Runtime就是最好的例子。
======================
This topic discusses the various .lib files that comprise the C run-time libraries as well as their associated compiler options and preprocessor directives.
The following libraries contain the C run-time library functions.
| C run-time library (without iostream or standard C++ library) | Characteristics | Option | Preprocessor directives |
|---|---|---|---|
| LIBC.LIB | Single-threaded, static link | /ML | |
| LIBCMT.LIB | Multithreaded, static link | /MT | _MT |
| MSVCRT.LIB | Multithreaded, dynamic link (import library for MSVCR71.DLL). Be aware that if you use the Standard C++ Library, your program will need MSVCP71.DLL to run. | /MD | _MT, _DLL |
| LIBCD.LIB | Single-threaded, static link (debug) | /MLd | _DEBUG |
| LIBCMTD.LIB | Multithreaded, static link (debug) | /MTd | _DEBUG, _MT |
| MSVCRTD.LIB | Multithreaded, dynamic link (import library for MSVCR71D.DLL) (debug) | /MDd | _DEBUG, _MT, _DLL |
If you link your program from the command line without a compiler option that specifies a C run-time library, the linker will use LIBC.LIB.
To build a debug version of your application, the _DEBUG flag must be defined and the application must be linked with a debug version of one of these libraries. For more information about using the debug versions of the library files, see CRT Debugging Techniques.
This version of Visual C++ is not conformant with the C99 standard.
Standard C++ Library
Note that starting in Visual Studio .NET 2003, Visual C++ will no longer ship the old iostream libraries. For details, see Upgrade to the Standard C++ Library and the Standard C++ Library Overview.
The new iostream functions, as well as many other new functions, exist in the Standard C++ Library:
| Standard C++ Library | Characteristics | Option | Preprocessor directives |
|---|---|---|---|
| LIBCP.LIB | Single-threaded, static link | /ML | |
| LIBCPMT.LIB | Multithreaded, static link | /MT | _MT |
| MSVCPRT.LIB | Multithreaded, dynamic link (import library for MSVCP71.dll) | /MD | _MT, _DLL |
| LIBCPD.LIB | Single-threaded, static link | /MLd | _DEBUG |
| LIBCPMTD.LIB | Multithreaded, static link | /MTd | _DEBUG, _MT |
| MSVCPRTD.LIB | Multithreaded, dynamic link (import library for MSVCP71D.DLL) | /MDd | _DEBUG, _MT, _DLL |
When you build a release version of your project, one of the basic C run-time libraries (LIBC.LIB, LIBCMT.LIB, and MSVCRT.LIB) is linked by default, depending on the compiler option you choose (single-threaded, multithreaded, or DLL). If you include a Standard C++ Library header in your code, a Standard C++ Library will be linked in automatically by Visual C++ at compile time. For example:
#include <ios>
What is the difference between msvcrt.dll and msvcr71.dll?
The msvcrt.dll is now a "known DLL," meaning that it is a system component owned and built by Windows. It is intended for future use only by system-level components. An application should use and redistribute msvcr71.dll, and it should avoid placing a copy or using an existing copy of msvcr71.dll in the system directory. Instead, the application should keep a copy of msvcr71.dll in its application directory with the program executable. Any application built with Visual C++ .NET using the /MD switch will necessarily use msvcr71.dll.
What problems exist if an application uses both msvcrt.dll and msvcr71.dll?
If you have a .lib or .obj file that needs to link to msvcrt.lib, then you should not have to recompile it to work with the new msvcrt.lib in Visual C++ .NET. The .lib or .obj file may rely on the sizes, field offsets, or member function names of various CRT classes or variables, and those should all still exist in a compatible way. When you relink against msvcrt.lib, your final EXE and DLL image will now have a dependency on msvcr71.dll instead of msvcrt.dll.
If you have more than one DLL or EXE, then you may have more than one CRT, whether or not you are using different versions of Visual C++. For example, statically linking the CRT into multiple DLLs can present the same problem. Developers encountering this problem with static CRTs have been instructed to compile with /MD to use the CRT DLL. Now that the CRT DLL has been renamed to msvcr71.dll, applications may have some components linked to msvcrt.dll and others to msvcr71.dll. If your DLLs pass CRT resources across the msvcrt.dll and msvcr71.dll boundary, you will encounter issues with mismatched CRTs and need to recompile your project with Visual C++ .NET.
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