I have received several questions about a case when developers find two or more references to different versions of CRT or MFC or ALT libraries in application manifest. Usually application manifest would look similar to the following:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0">
<assemblyIdentity type="win32" name="Microsoft.VC80.CRT" version="8.0.50727.762" processorArchitecture="x86" publicKeyToken="1fc8b3b9a1e18e3b"></assemblyIdentity>
<assemblyIdentity type="win32" name="Microsoft.VC80.CRT" version="8.0.50608.0" processorArchitecture="x86" publicKeyToken="1fc8b3b9a1e18e3b"></assemblyIdentity>
Notice underlined version of assembly. This manifest tells Windows loader to load two different versions of the same assembly. The loader is going to do what it is told to. But the problem arises when it can only find one version (50608) of them. There are two cases when this may happen:
1) The oldest version of VC++ library is installed in WinSxS folder. For example, author of the application may have redistributed VS2005 RTM version of CRT library using MSMs or VCRedist.EXE, but ones parts of application were rebuilt with VS2005 SP1 and deployed to the same machine, SP1 versions of MSMs or VCRedist.EXE were not deployed to the same machine.
2) It is not possible to have two versions of a private assembly in one folder. For example, an author of an application has deployed the RTM version of CRT library as a private assembly in application’s local folder. After application is rebuilt with SP1, the author faces a challenge of having two copies of same files/folders in application local folder. If she keeps RTM version, Windows loader is going to complain about SP1 version missing. If she keeps SP1 version, Windows loaders is going to fail to find RTM version. Windows shows a message box which says :”The application has failed to start because of side-by-side configuration is incorrect,” and event viewer shows error details similar to “Activation context generation failed for "…\foo.exe".Error in manifest or policy file. A component version required by the application conflicts with another component version already active.” Bottom line, application does not start.
The root cause of the issue is that not all parts of application’s source code are built with the same version of VC++ libraries and tools. The linker catches some cases and reports errors when it tries to link objects and libraries built with different versions of compiler. However it is still possible to get pass the linker and an application may get these two dependencies in its manifest.
There is one solution to the problem and two workarounds.
The solution. To fix the problem, you must rebuild all parts of your code with the newest toolset and libraries. Make sure you have cleaned up all binaries built by the old toolset and started full rebuild of the whole source base. Also check that old versions of headers and import libraries for VC++ libraries are not on INCLUDE and LIB path and they are not used during the build.
Workaround#1: Install the newer version (8.0.50727.762 in this case) of VC++ MSMs or VCRedist.EXE on a machine where your application is going to run. Once policy for VC++ assemblies is installed on that machine they are going to redirect all loads of older versions (8.0.50608.0) to the newest version available on the machine.
Workaround#2: If you are redistributing VC++ libraries in application’s local folder, you need to add an application configuration file that redirects an attempt to load 8.0.50608.0 version to 8.0.50727.762 version. Configuration file has to have same name as the exe plus .config extension and has to be right next to exe or embedded into the EXE. Here is an example of a configuration file that one would use to resolve issue with the manifest from above:
<assemblyIdentity type="win32" name="Microsoft.VC80.CRT" processorArchitecture="x86" publicKeyToken="1fc8b3b9a1e18e3b"></assemblyIdentity>
<bindingRedirect oldVersion="8.0.41204.256-8.0.50727.762" newVersion="8.0.50727.762"/>
This file basically redirects attempts to load any version of VC CRT greater or equal to 8.0.41204.256 (VS2005 Beta 1) and less than 8.0.50727.762(VS2005 SP1) to load VS2005 SP1 version of VC CRT. It is similar to what the policy file does for a case when CRT is installed into WinSxS folder.
Overall my recommendation is to never use static libraries for which you do not have a source code. Using a static library without its source always puts a set of restrictions on build configuration of a binary that consumes it. There are ways to build a “clean” static library, but they are not well known among developers and it is very rare to find a static library that can be consumed in a code built with different versions of compiler, linker and libraries. If source code is not provided, I would only take a dependency on a DLL and only if its APIs are cleanly designed to obey rules of data exchange across DLL boundary. COM and .Net class assemblies are designed to address this problem and they are the easiest technologies to use in this scenario.