unresolved external symbol imp fprintf and imp iob func SDL2

Question

Could someone explain what the        imp  fprintf   and       imp    iob func   unresolved external means   Because I get these errors when I m trying to compile   1 gt SDL2main lib SDL windows main obj    error LNK2019  unresolved external symbol   imp  fprintf referenced in function  ShowError 1 gt SDL2main lib SDL windows main obj    error LNK2019  unresolved external symbol   imp    iob func referenced in function  ShowError 1 gt E  Documents Visual Studio 2015 Projects SDL2 Test Debug SDL2 Test exe   fatal error LNK1120  2 unresolved externals   I can already say that the problem is not from linking wrong  I have linked everything up correctly  but for some reason it won t compile   I m trying to use SDL2   I m using Visual Studio 2015 as compiler   I have linked to SDL2 lib and SDL2main lib in Linker -  Input -  Additional Dependencies and I have made sure that the VC   Directories are correct

User · Accepted Answer

I have finally figured out why this is happening !

In visual studio 2015, stdin, stderr, stdout are defined as follow :

#define stdin  (__acrt_iob_func(0))
#define stdout (__acrt_iob_func(1))
#define stderr (__acrt_iob_func(2))

But previously, they were defined as:

#define stdin  (&__iob_func()[0])
#define stdout (&__iob_func()[1])
#define stderr (&__iob_func()[2])

So now __iob_func is not defined anymore which leads to a link error when using a .lib file compiled with previous versions of visual studio.

To solve the issue, you can try defining __iob_func() yourself which should return an array containing {*stdin,*stdout,*stderr}.

Regarding the other link errors about stdio functions (in my case it was sprintf()), you can add legacy_stdio_definitions.lib to your linker options.

User · Answer

Microsoft has a special note on this  https   msdn microsoft com en-us library bb531344 aspx BK CRT       The printf and scanf family of functions are now defined inline       The definitions of all of the printf and scanf functions have been   moved inline into stdio h  conio h  and other CRT headers    This is a breaking change that leads to a linker error  LNK2019    unresolved external symbol  for any programs that declared these   functions locally without including the appropriate CRT headers  If   possible  you should update the code to include the CRT headers  that   is  add  include   and the inline functions  but if you do   not want to modify your code to include these header files  an   alternative solution is to add an additional library to your linker   input  legacy stdio definitions lib       To add this library to your linker input in the IDE  open the context   menu for the project node  choose Properties  then in the Project   Properties dialog box  choose Linker  and edit the Linker Input to add   legacy stdio definitions lib to the semi-colon-separated list       If your project links with static libraries that were compiled with a   release of Visual C   earlier than 2015  the linker might report an   unresolved external symbol  These errors might reference internal   stdio definitions for  iob   iob func  or related imports for   certain stdio functions in the form of   imp    Microsoft   recommends that you recompile all static libraries with the latest   version of the Visual C   compiler and libraries when you upgrade a   project  If the library is a third-party library for which source is   not available  you should either request an updated binary from the   third party or encapsulate your usage of that library into a separate   DLL that you compile with the older version of the Visual C   compiler   and libraries

User · Answer

I don t know why but    ifdef main  undef main  endif   After the includes but before your main should fix it from my experience

User · Answer

To bring more confusion in this already rich thread  I happened to bump in the same unresolved external on fprintf  main obj   error LNK2019  unresolved external symbol   imp  fprintf referenced in function  GenerateInfoFile   Even if in my case it was in a rather different context   under Visual Studio 2005  Visual Studio 8 0  and the error was happening in my own code  the very same I was compiling   not a third party   It happened that this error was triggered by  MD option in my compiler flags  Switching to  MT removed the issue  This is weird because usually  linking statically  MT  raises more problem than dynamically  MD     but just in case it serves other  I put it there

User · Answer

In my case  this error comes from my trial to remove dependencies to MSVC-version dependent runtime library DLL  msvcr10 dll or so  and or remove static runtime library too  to remove excess fat from my executables   So I use  NODEFAULTLIB linker switch  my self-made  msvcrt-light lib   google for it when you need   and mainCRTStartup     WinMainCRTStartup   entries   It is IMHO since Visual Studio 2015  so I stuck to older compilers   However  defining symbol  NO CRT STDIO INLINE removes all hassle  and a simple  Hello World  application is again 3 KB small and doesn t depend to unusual DLLs  Tested in Visual Studio 2017

User · Answer

To link means not to work properly  Digging into stdio h of VS2012 and VS2015 the following worked for me  Alas  you have to decide if it should work for one of   stdin  stdout  stderr    never more than one   extern  C  FILE    cdecl   iob func         struct  iobuf VS2012          Microsoft Visual Studio 11 0 VC include stdio h  56         char   ptr          int    cnt          char   base          int    flag          int    file          int    charbuf          int    bufsiz          char   tmpfname            VS2015 has only FILE   struct  void        int const count   sizeof  iobuf VS2012    sizeof FILE             stdout       return  FILE    amp    acrt iob func 1 - gt  Placeholder  - count           stderr     return  FILE    amp    acrt iob func 2 - gt  Placeholder  - 2   count

User · Answer

I had the same issue in VS2015  I have solved it by compiling the SDL2 sources in VS2015    Go to http   libsdl org download-2 0 php and download SDL 2 source code  Open SDL VS2013 sln in VS2015  You will be asked to convert the projects  Do it  Compile SDL2 project  Compile SDL2main project  Use the new generated output files SDL2main lib  SDL2 lib and SDL2 dll in your SDL 2 project in VS2015

User · Answer

I managed to fix the problem    The source of the error was this line of code  that can be found in the SDLmain source code   fprintf stderr    s   s n   title  message     So what I did was to edit the source code in SDLmain of that line too   fprintf   s   s n   title  message     And then I built the SDLmain and copied and replaced the old SDLmain lib in my SDL2 library directory with the newly built and edited    Then when I ran my program with SDL2 no error messages came up and to code ran smoothly   I don t know if this will bite me later  but so for everything is going great

User · Answer

Paste this code in any of your source files and re-build  Worked for me     include stdio h  FILE  iob 3    FILE    cdecl   iob func void      iob 0     stdin    iob 0     stdout    iob 0     stderr   return  iob

User · Answer

Maybe this might help you  I added Shell32 lib to my Linker -- gt  Input -- gt  Additional Dependencies and it stopped this error  I found out about it from this post  https   discourse libsdl org t windows-build-fails-with-missing-symbol-imp-commandlinetoargvw 27256 3

User · Answer

This can happen when you link to msvcrt dll instead of msvcr10 dll  or similar   which is a good plan  Because it will free you up to redistribute your Visual Studio s runtime library inside your final software package   That workaround helps me  at Visual Studio 2008     if  MSC VER  gt   1400  undef stdin  undef stdout  undef stderr extern  C   CRTIMP extern FILE  iob     define stdin    iob  define stdout    iob 1   define stderr    iob 2   endif   This snippet is not needed for Visual Studio 6 and its compiler  Therefore the  ifdef

User · Answer

To Milan Babu  kov  IMO  this is exactly what the replacement function should look like  -   FILE  iob       stdin   stdout   stderr    extern  C  FILE     cdecl   iob func void        return  iob

User · Answer

Use the pre-compiled SDL2main lib and SDL lib for your VS2015 project s library   https   buildbot libsdl org sdl-builds sdl-visualstudio sdl-visualstudio-2225 zip

User · Answer

My advice is to not  try to  implement   iob func   While fixing these errors   libpngd v110 lib pngrutil obj    error LNK2001  unresolved external symbol    iob func curllib v110 lib mprintf obj    error LNK2001  unresolved external symbol    iob func  I tried the other answers  solutions  but in the end  returning a FILE  C-array doesn t match up with an array of Windows  internal IOB structs   Volker is right that it ll never work for more than one of stdin  stdout or stderr   If a library actually USES one of those streams  it will crash  As long as your program doesn t cause the lib to use them  you ll never know  For example  png default error writes to stderr when the CRC doesn t match in the PNG s metadata   Normally not a crash-worthy issue   Conclusion  It s not possible to mix VS2012  Platform Toolset v110 v110 xp  and VS2015  libraries  if they use stdin  stdout and or stderr   Solution  Recompile your libraries that have   iob func unresolved symbols with your current version of VS and a matching Platform Toolset

User · Answer

For anyone who is still looking for an answer where the above tricks didn t work  Static linking is the way to solve this problem  Change your Runtime library settings as below  Project properties -- gt  C C   -- gt  Code generation -- gt  Runtime Library -- gt  Multi-threaded Debug   MTd  instead of  MDd

User · Answer

As answered above  the right answer is to compile everything with VS2015  but for interest the following is my analysis of the problem   This symbol does not appear to be defined in any static library provided by Microsoft as part of VS2015  which is rather peculiar since all others are  To discover why  we need to look at the declaration of that function and  more importantly  how it s used   Here s a snippet from the Visual Studio 2008 headers    CRTIMP FILE     cdecl   iob func void    define stdin   amp   iob func   0    define stdout   amp   iob func   1    define stderr   amp   iob func   2     So we can see that the job of the function is to return the start of an array of FILE objects  not handles  the  FILE    is the handle  FILE is the underlying opaque data structure storing the important state goodies   The users of this function are the three macros stdin  stdout and stderr which are used for various fscanf  fprintf style calls   Now let s take a look at how Visual Studio 2015 defines the same things    ACRTIMP ALT FILE    cdecl   acrt iob func unsigned    define stdin    acrt iob func 0    define stdout    acrt iob func 1    define stderr    acrt iob func 2     So the approach has changed for the replacement function to now return the file handle rather than the address of the array of file objects  and the macros have changed to simply call the function passing in an identifying number   So why can t they we provide a compatible API  There are two key rules which Microsoft can t contravene in terms of their original implementation via   iob func    There must be an array of three FILE structures which can be indexed in the same manner as before  The structural layout of FILE cannot change    Any change in either of the above would mean existing compiled code linked against that would go badly wrong if that API is called   Let s take a look at how FILE was is defined   First the VS2008 FILE definition   struct  iobuf           char   ptr          int    cnt          char   base          int    flag          int    file          int    charbuf          int    bufsiz          char   tmpfname             typedef struct  iobuf FILE    And now the VS2015 FILE definition   typedef struct  iobuf       void   Placeholder    FILE    So there is the crux of it  the structure has changed shape  Existing compiled code referring to   iob func relies upon the fact that the data returned is both an array that can be indexed and that in that array the elements are the same distance apart   The possible solutions mentioned in the answers above along these lines would not work  if called  for a few reasons   FILE  iob       stdin   stdout   stderr    extern  C  FILE     cdecl   iob func void        return  iob      The FILE array  iob would be compiled with VS2015 and so it would be laid out as a block of structures containing a void   Assuming 32-bit alignment  these elements would be 4 bytes apart  So  iob 0  is at offset 0   iob 1  is at offset 4 and  iob 2  is at offset 8  The calling code will instead expect FILE to be much longer  aligned at 32 bytes on my system  and so it will take the address of the returned array and add 0 bytes to get to element zero  that one is okay   but for  iob 1  it will deduce that it needs to add 32 bytes and for  iob 2  it will deduce that it needs to add 64-bytes  because that s how it looked in the VS2008 headers   And indeed the disassembled code for VS2008 demonstrates this   A secondary issue with the above solution is that it copies the content of the FILE structure   stdin   not the FILE   handle  So any VS2008 code would be looking at a different underlying structure to VS2015  This might work if the structure only contained pointers  but that s a big risk  In any case the first issue renders this irrelevant   The only hack I ve been able to dream up is one in which   iob func walks the call stack to work out which actual file handle they are looking for  based on the offset added to the returned address  and returns a computed value such that it gives the right answer  This is every bit as insane as it sounds  but the prototype for x86 only  not x64  is listed below for your amusement  It worked okay in my experiments  but your mileage may vary - not recommended for production use    include  lt windows h gt   include  lt stdio h gt   include  lt dbghelp h gt       define LOG      if defined  M IX86    define GET CURRENT CONTEXT c  contextFlags      do         c ContextFlags   contextFlags          asm    call x         asm x  pop eax         asm    mov c Eip  eax         asm    mov c Ebp  ebp         asm    mov c Esp  esp       while 0     else     This should work for 64-bit apps  but doesn t     define GET CURRENT CONTEXT c  contextFlags      do         c ContextFlags   contextFlags        RtlCaptureContext  amp c       while 0     endif  FILE     cdecl   iob func void        CONTEXT c     0        STACKFRAME64 s     0        DWORD imageType      HANDLE hThread   GetCurrentThread        HANDLE hProcess   GetCurrentProcess         GET CURRENT CONTEXT c  CONTEXT FULL     ifdef  M IX86     imageType   IMAGE FILE MACHINE I386      s AddrPC Offset   c Eip      s AddrPC Mode   AddrModeFlat      s AddrFrame Offset   c Ebp      s AddrFrame Mode   AddrModeFlat      s AddrStack Offset   c Esp      s AddrStack Mode   AddrModeFlat   elif  M X64     imageType   IMAGE FILE MACHINE AMD64      s AddrPC Offset   c Rip      s AddrPC Mode   AddrModeFlat      s AddrFrame Offset   c Rsp      s AddrFrame Mode   AddrModeFlat      s AddrStack Offset   c Rsp      s AddrStack Mode   AddrModeFlat   elif  M IA64     imageType   IMAGE FILE MACHINE IA64      s AddrPC Offset   c StIIP      s AddrPC Mode   AddrModeFlat      s AddrFrame Offset   c IntSp      s AddrFrame Mode   AddrModeFlat      s AddrBStore Offset   c RsBSP      s AddrBStore Mode   AddrModeFlat      s AddrStack Offset   c IntSp      s AddrStack Mode   AddrModeFlat   else  error  Platform not supported    endif      if   StackWalk64 imageType  hProcess  hThread   amp s   amp c  NULL  SymFunctionTableAccess64  SymGetModuleBase64  NULL          ifdef LOG         printf  Error  0x 08X  Address   p  n   GetLastError     LPVOID s AddrPC Offset    endif         return NULL             if  s AddrReturn Offset    0                return NULL                       unsigned char const   assembly    unsigned char const    s AddrReturn Offset    ifdef LOG         printf  Code bytes proceeding call to   iob func   p   02X  02X  02X n   assembly   assembly    assembly   1     assembly   2     endif         if   assembly    0x83  amp  amp    assembly   1     0xC0  amp  amp     assembly   2     0x20      assembly   2     0x40                         if    assembly   2     32                                return  FILE    unsigned char   stdout - 32                             if    assembly   2     64                                return  FILE    unsigned char   stderr - 64                                    else                       return stdin                      return NULL

User · Answer

A more recent solution to this problem  Use the more recent sdl libs on   https   buildbot libsdl org sdl-builds sdl-visualstudio  C M O D   They seem to have fixed the problem  although it s only the 32 bit library  I think

User · Answer

I resolve this problem with following function  I use Visual Studio 2019   FILE    cdecl   iob func void        FILE  iob        stdin   stdout   stderr        return  iob      because stdin Macro defined function call    stdin  expression is cannot used global array initializer  But local array initialier is possible  sorry  I am poor at english

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