今天用VS2019編譯一個在VS2008下Coding的工程的時候，VS給出了一堆鏈接錯誤信息，如下圖所示的一些錯誤：
Error 47 error LNK2019: unresolved external symbol "public: __thiscall std::_Mutex::~_Mutex(void)" (??1_Mutex@std@@QAE@XZ) referenced in function "public: void __thiscall std::ios_base::clear(int,bool)" (?clear@ios_base@std@@QAEXH_N@Z) D:\server\mysqlpp.lib(dbdriver.obj) server
Error 48 error LNK2001: unresolved external symbol "public: __thiscall std::_Mutex::~_Mutex(void)" (??1_Mutex@std@@QAE@XZ) D:\server\mysqlpp.lib(datetime.obj) server
Error 49 error LNK2001: unresolved external symbol "public: __thiscall std::_Mutex::~_Mutex(void)" (??1_Mutex@std@@QAE@XZ) D:\server\mysqlpp.lib(stadapter.obj) server
Error 50 error LNK2001: unresolved external symbol "public: __thiscall std::_Mutex::~_Mutex(void)" (??1_Mutex@std@@QAE@XZ) D:\server\mysqlpp.lib(sqlstream.obj) server
Error 51 error LNK2001: unresolved external symbol "public: __thiscall std::_Mutex::~_Mutex(void)" (??1_Mutex@std@@QAE@XZ) D:\server\mysqlpp.lib(connection.obj) server
Error 52 error LNK2001: unresolved external symbol "public: __thiscall std::_Mutex::~_Mutex(void)" (??1_Mutex@std@@QAE@XZ) D:\server\mysqlpp.lib(mystring.obj) server
Error 53 error LNK2001: unresolved external symbol "public: __thiscall std::_Mutex::~_Mutex(void)" (??1_Mutex@std@@QAE@XZ) D:\server\mysqlpp.lib(row.obj) server
Error 54 error LNK2001: unresolved external symbol "public: __thiscall std::_Mutex::~_Mutex(void)" (??1_Mutex@std@@QAE@XZ) D:\server\mysqlpp.lib(query.obj) server
Error 55 error LNK2001: unresolved external symbol "long const std::_BADOFF" (?_BADOFF@std@@3JB) D:\server\mysqlpp.lib(dbdriver.obj) server
Error 56 error LNK2001: unresolved external symbol "long const std::_BADOFF" (?_BADOFF@std@@3JB) D:\server\mysqlpp.lib(datetime.obj) server
Error 57 error LNK2001: unresolved external symbol "long const std::_BADOFF" (?_BADOFF@std@@3JB) D:\server\mysqlpp.lib(stadapter.obj) server
Error 58 error LNK2001: unresolved external symbol "long const std::_BADOFF" (?_BADOFF@std@@3JB) D:\server\mysqlpp.lib(sqlstream.obj) server
Error 59 error LNK2001: unresolved external symbol "long const std::_BADOFF" (?_BADOFF@std@@3JB) D:\server\mysqlpp.lib(connection.obj) server
Error 60 error LNK2001: unresolved external symbol "long const std::_BADOFF" (?_BADOFF@std@@3JB) D:\server\mysqlpp.lib(mystring.obj) server
Error 61 error LNK2001: unresolved external symbol "long const std::_BADOFF" (?_BADOFF@std@@3JB) D:\server\mysqlpp.lib(row.obj) server
Error 62 error LNK2001: unresolved external symbol "long const std::_BADOFF" (?_BADOFF@std@@3JB) D:\server\mysqlpp.lib(query.obj) server
Error 63 error LNK2001: unresolved external symbol "public: static void __cdecl std::_String_base::_Xran(void)" (?_Xran@_String_base@std@@SAXXZ) D:\server\mysqlpp.lib(qparms.obj) server
Error 64 error LNK2001: unresolved external symbol "public: static void __cdecl std::_String_base::_Xran(void)" (?_Xran@_String_base@std@@SAXXZ) D:\server\mysqlpp.lib(sqlstream.obj) server
Error 65 error LNK2001: unresolved external symbol "public: static void __cdecl std::_String_base::_Xran(void)" (?_Xran@_String_base@std@@SAXXZ) D:\server\mysqlpp.lib(options.obj) server
Error 66 error LNK2001: unresolved external symbol "public: static void __cdecl std::_String_base::_Xran(void)" (?_Xran@_String_base@std@@SAXXZ) D:\server\mysqlpp.lib(field_types.obj) server
Error 67 error LNK2019: unresolved external symbol "public: static void __cdecl std::_String_base::_Xran(void)" (?_Xran@_String_base@std@@SAXXZ) referenced in function "public: char __thiscall mysqlpp::SQLTypeAdapter::at(unsigned int)const " (?at@SQLTypeAdapter@mysqlpp@@QBEDI@Z) D:\server\mysqlpp.lib(stadapter.obj) server
Error 68 error LNK2001: unresolved external symbol "public: static void __cdecl std::_String_base::_Xran(void)" (?_Xran@_String_base@std@@SAXXZ) D:\server\mysqlpp.lib(manip.obj) server
Error 69 error LNK2001: unresolved external symbol "public: static void __cdecl std::_String_base::_Xran(void)" (?_Xran@_String_base@std@@SAXXZ) D:\server\mysqlpp.lib(null.obj) server
Error 70 error LNK2001: unresolved external symbol "public: static void __cdecl std::_String_base::_Xran(void)" (?_Xran@_String_base@std@@SAXXZ) D:\server\mysqlpp.lib(datetime.obj) server
Error 71 error LNK2001: unresolved external symbol "public: static void __cdecl std::_String_base::_Xran(void)" (?_Xran@_String_base@std@@SAXXZ) D:\server\mysqlpp.lib(type_info.obj) server
Error 72 error LNK2001: unresolved external symbol "public: static void __cdecl std::_String_base::_Xran(void)" (?_Xran@_String_base@std@@SAXXZ) D:\server\mysqlpp.lib(vallist.obj) server
Error 73 error LNK2001: unresolved external symbol "public: static void __cdecl std::_String_base::_Xran(void)" (?_Xran@_String_base@std@@SAXXZ) D:\server\mysqlpp.lib(field_names.obj) server
Error 74 error LNK2001: unresolved external symbol "public: static void __cdecl std::_String_base::_Xran(void)" (?_Xran@_String_base@std@@SAXXZ) D:\server\mysqlpp.lib(query.obj) server
Error 75 error LNK2001: unresolved external symbol "public: static void __cdecl std::_String_base::_Xran(void)" (?_Xran@_String_base@std@@SAXXZ) D:\server\mysqlpp.lib(dbdriver.obj) server
Error 76 error LNK2001: unresolved external symbol "public: static void __cdecl std::_String_base::_Xran(void)" (?_Xran@_String_base@std@@SAXXZ) D:\server\mysqlpp.lib(tcp_connection.obj) server
Error 82 error LNK2001: unresolved external symbol "public: static void __cdecl std::_String_base::_Xlen(void)" (?_Xlen@_String_base@std@@SAXXZ) D:\server\mysqlpp.lib(null.obj) server
問題總結：
因爲靜態鏈接庫mysqlpp.lib在舊版本IDE上編譯的，所以string類中符號被解析成形如 static void __cdecl _Xran()或static void __cdecl _Xlen()
而在高版本的VS2019上string中的_Xran與_Xlen符號則被解析成了__declspec(noreturn) void _Xran() const或__declspec(noreturn) void _Xlen() const
所以纔會在鏈接過程中出現上述開頭出現的一堆問題
#include <string>
namespace std2008
{
class _String_base_2008
{
public:
{
__declspec(dllexport) void _Xlen2008(void) const;
__declspec(dllexport) void _Xran2008(void) const;
};
};
void std2008::_String_base_2008::_Xran2008 () const
{
std::_String_base::_Xran ();
}
void std2008::_String_base_2008::_Xlen2008 () const
{
std::_String_base::_Xlen ();
}
Save this code as "compat.cpp" and compile with
cl /D_DLL_EXPORT /EHsc /LD compat.cpp /link
Now lets examine the lib file, that has been created:
dumpbin /exports compat.lib
In my case it looks like this:
Dump of file compat.lib
File Type: LIBRARY
Exports
ordinal name
?_Xlen2008@_String_base_2008@std2008@@QBEXXZ (public: void __thiscall std2008::_String_base_2008::_Xlen2008(void)const )
?_Xran2008@_String_base_2008@std2008@@QBEXXZ (public: void __thiscall std2008::_String_base_2008::_Xran2008(void)const )
When looking at the linker errors about missing symbols, you see the decoration that is required. In your case its "?_Xran@_String_base@std@@SAXXZ" and "?_Xlen@_String_base@std@@SAXXZ"
The last step is to tell the linker to create a library that maps the standard decorated names to a another name using the symbols from your linker error and the names taken from dumpbin.
Cl /EHsc /LD compat.cpp /link /export:?_Xran@_String_base@std@@SAXXZ=?_Xran2008@_String_base_2008@std2008@@QBEXXZ /export:?_Xlen@_String_base@std@@SAXXZ=?_Xlen2008@_String_base_2008@std2008@@QBEXXZ
Cl /EHsc /LD compat1.cpp /link /export:??0exception@std@@QAE@ABQBD@Z=??exception_2008@std2008@@QAEXABQBD@Z
Now add the "compat.lib" library as additional library to your project and now it should link successfully.
Compact.c代碼
#include <string>
namespace std2008
{
class _String_base_2008
{
public:
__declspec(dllexport) void _Xlen2008(void) const;
__declspec(dllexport) void _Xran2008(void) const;
};
};
void std2008::_String_base_2008::_Xran2008 () const
{
std::_String_base::_Xran ();
}
void std2008::_String_base_2008::_Xlen2008 () const
{
std::_String_base::_Xlen ();
}
生成DLL和LIB
cl /D_DLL_EXPORT /EHsc /LD compat.cpp /link
生成可用的LIB
Cl /EHsc /LD compat.cpp /link /export:?_Xran@_String_base@std@@SAXXZ=?_Xran2008@_String_base_2008@std2008@@QBEXXZ /export:?_Xlen@_String_base@std@@SAXXZ=?_Xlen2008@_String_base_2008@std2008@@QBEXXZ
Compact1.c代碼
#include <string>
namespace std2008
{
class exception_2008
{
public:
__declspec(dllexport) exception_2008(char const * const & ch);
};
};
std2008::exception_2008::exception_2008(char const * const & ch)
{
std::exception::exception (ch);
}
生成DLL和LIB
cl /D_DLL_EXPORT /EHsc /LD compat1.cpp /link
生成可用的LIB
Cl /EHsc /LD compat1.cpp /link /export:??0
exception@std@@QAE@ABQBD@Z=??exception_2008@std2008@@QAEXABQBD@Z
將生成的compat.dll和compat1.dll拷貝至EXE目錄，compat.lib和compat1.lib則拷貝至源文件與mysqlpp.lib同一目錄中，即可順利編譯了！！