If the lib is added explicitly, you're right -- it probably won't break anything.
However, there are actually three CRTs. libc (single-threaded static), libcmt (multi-threaded static), and msvcrt (multi-threaded DLL). libc is no longer supported (there is no longer any such thing as a single-threaded Windows app because things like signals can come in on separate threads). So adding a nodefaultlib for msvcrt is not just like the nodefaultlib for libc. It would be like a nodefaultlib for libcmt. Lib conflicts are scary. They work only because you are lucky and because the Microsoft CRT developers worked very hard to make things work ok most of the time. However, there are some functions that don't work ok, and the list of functions that don't work ok is subject to change at any time. And sometimes you might be using a function that mostly works ok except for some strange edge cases. Better to just avoid the whole issue if possible. As for "allowing" multiple CRTs, I was referring to the warning. It warns when you link with multiple CRTs at the same time. In your case, the conflict looks scary because you have linked with _dup but not with free... You should only use one CRT in an EXE or DLL. Any time you use more than one within the same executable, you're in undefined territory and while things may work, things could go wrong at any time. There's nothing wrong with msvcr71.dll or msvcr80.dll. In fact, they have many bug fixes and performance improvements over msvcrt.dll. However, if you link against one of them, it has to be installed on the target machine or the EXE/DLL won't load, while msvcrt.dll is always present on every copy of Windows. That said, you might run into an old versions of msvcrt.dll that is missing functions you need (each new version of Windows has added new functions to msvcrt.dll), while you pretty much know what you are getting when you use msvcr71 or msvcr80. -----Original Message----- From: Yongwei Wu [mailto:[EMAIL PROTECTED] Sent: Thursday, May 17, 2007 7:15 AM To: Doug Cook Cc: Bram Moolenaar; Vim-dev mailing list Subject: Re: MSVC build option about default library MSVCRT Hi Doug, On 17/05/07, Doug Cook <[EMAIL PROTECTED]> wrote: > Bram is wise. No objection here ;-). > Adding a nodefaultlib:msvcrt could potentially break things if you set > USE_MSVCRT=1 to use the CRT DLL instead of statically linking the CRT. The > problem is that you're linking a static-CRT version of Vim with DLL-CRT > versions of ActiveState components. The problem is not with Vim's makefile. Adding /nodefaultlib:msvcrt does not affect USE_MSVCRT=1, which will add the NON-default library msvcrt.lib explicitly. In fact, I think /nodefaultlib:msvcrt is really symmetrical with the current setting. We already have /nodefaultlib:libc, which disables the default static libc. Why should we allow default dynamic libc while disabling default static libc? > Generally, if you have lib conflicts, it means you've done something wrong. > In this case, you have one OBJ that was compiled for use with the static > CRT, and another OBJ that was compiled for use with the dynamically-linked > CRT. Each of them tell the linker "you should probably link me with this > particular CRT". Luckily, the linker is smart enough to only allow one CRT > at a time. Lib conflicts are something wrong, but not necessarily serious. It is a serious problem only if one does some foolish things like malloc in one CRT and free in another. Also, the linker does allow two CRTs at the same time, and which occurred to me, if I did not add /nodefaultlib:msvcrt. LibcMT will be linked, but the following five functions are imported from MSVCR71.dll: _fileno _chdir _fdopen _dup _putenv _stat _dup2 > For a standalone program, statically linking with the CRT is generally the > way to go, so Vim defaults to doing this. Using the CRT DLL saves about 150k > in disk space, but the CRT DLL is 400-800k, depending on which version of > Visual C++ you're using. The CRT is potentially already in memory in another > process, so this may or may not save memory at runtime. > > For a program that interacts with other DLLs (such as loading Perl, Python, > Ruby, etc. DLLs at runtime), the CRT DLL starts to make more sense. In > addition to saving disk space (one CRT DLL instead of 150k of static CRT in > each executable), you save memory (one CRT DLL loaded, and all modules share > the same heap) and in some cases you avoid bugs (only one CRT so you don't > have conflicting CRT settings like locale). However, you now have to > redistribute the CRT with your product, and starting with VC 8.0, you have > to get the CRT's manifest correctly embedded into your EXE and DLLs. Another problem with CRT DLL is that different MSVC versions will make the resulting executable dependent on different CRT DLLs. Linking with MSVCRT.LIB in MSVC 7.1 results in the dependency on MSVCR71.DLL instead of MSVCRT.DLL. This is not something we like, I suppose. Best regards, Yongwei -- Wu Yongwei URL: http://wyw.dcweb.cn/
