Resolving LNK4098 defaultlib MSVCRT conflicts with

Question

This warning   LINK   warning LNK4098  defaultlib  MSVCRT  conflicts   with use of other libs  use  NODEFAULTLIB library   is a fairly common warning in Visual Studio  I d like to understand the exact reason for it and the right way  if at all  to handle it   This comes up in a debug build  compiled with  MDd  The project is linked to things like windows Version dll and pdh dll which themselves link with MSVCRT dll  Obviously  I don t have the debug versions of these and can t compile them     So I added  NODEFAULTLIB MSVCRT to the linker command line and it actually did remove the warning  But what does this actually do  And why is it necessary

User · Answer

There are 4 versions of the CRT link libraries present in vc\lib:

libcmt.lib: static CRT link library for a release build (/MT)
libcmtd.lib: static CRT link library for a debug build (/MTd)
msvcrt.lib: import library for the release DLL version of the CRT (/MD)
msvcrtd.lib: import library for the debug DLL version of the CRT (/MDd)

Look at the linker options, Project + Properties, Linker, Command Line. Note how these libraries are not mentioned here. The linker automatically figures out what /M switch was used by the compiler and which .lib should be linked through a #pragma comment directive. Kinda important, you'd get horrible link errors and hard to diagnose runtime errors if there was a mismatch between the /M option and the .lib you link with.

You'll see the error message you quoted when the linker is told both to link to msvcrt.lib and libcmt.lib. Which will happen if you link code that was compiled with /MT with code that was linked with /MD. There can be only one version of the CRT.

/NODEFAULTLIB tells the linker to ignore the #pragma comment directive that was generated from the /MT compiled code. This might work, although a slew of other linker errors is not uncommon. Things like errno, which is a extern int in the static CRT version but macro-ed to a function in the DLL version. Many others like that.

Well, fix this problem the Right Way, find the .obj or .lib file that you are linking that was compiled with the wrong /M option. If you have no clue then you could find it by grepping the .obj/.lib files for "/MT"

Btw: the Windows executables (like version.dll) have their own CRT version to get their job done. It is located in c:\windows\system32, you cannot reliably use it for your own programs, its CRT headers are not available anywhere. The CRT DLL used by your program has a different name (like msvcrt90.dll).

User · Answer

I get this every time I want to create an application in VC     Right-click the project  select Properties then under  Configuration properties   C C     Code Generation   select  Multi-threaded Debug   MTd   for Debug configuration   Note that this does not change the setting for your Release configuration - you ll need to go to the same location and select  Multi-threaded   MT   for Release

User · Answer

Right-click the project  select Properties then under  Configuration properties   Linker   Input   Ignore specific Library  and write msvcrtd lib

User · Answer

It means that one of the dependent dlls is compiled with a different run-time library   Project -  Properties -  C C   -  Code Generation -  Runtime Library  Go over all the libraries and see that they are compiled in the same way   More about this error in this link   warning LNK4098  defaultlib  LIBCD  conflicts with use of other libs

User · Answer

IMO this link from Yochai Timmer was very good and relevant but painful to read  I wrote a summary  Yochai  if you ever read this  please see the note at the end   For the original post read   warning LNK4098  defaultlib  quot LIBCD quot  conflicts with use of other libs Error  LINK   warning LNK4098  defaultlib  quot LIBCD quot  conflicts with use of other  libs  use  NODEFAULTLIB library  Meaning  one part of the system was compiled to use a single threaded standard  libc  library with debug information  libcd  which is statically linked while another part of the system was compiled to use a multi-threaded standard library without debug information which resides in a DLL and uses dynamic linking  How to resolve   Ignore the warning  after all it is only a warning  However  your program now contains multiple instances of the same functions   Use the linker option  NODEFAULTLIB lib  This is not a complete solution  even if you can get your program to link this way you are ignoring a warning sign  the code has been compiled for different environments  some of your code may be compiled for a single threaded model while other code is multi-threaded         trawl through all your libraries and ensure they have the correct link settings    In the latter  as it in mentioned in the original post  two common problems can arise     You have a third party library which is linked differently to your application   You have other directives embedded in your code  normally this is the MFC  If any modules in your system link against MFC all your modules must nominally link against the same version of MFC     For those cases  ensure you understand the problem and decide among the solutions   Note   I wanted to include that summary of Yochai Timmer s link into his own answer but since some people have trouble to review edits properly I had to write it in a separate answer  Sorry

[visual-studio] Resolving LNK4098: defaultlib 'MSVCRT' conflicts with

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