INFO: Visual C++ 5.0 Readme, Compiler, Linker and Utilities

ID: Q165687

The information in this article applies to:

Microsoft Visual C++, 32-bit Editions, version 5.0

SUMMARY

Compiler, Linker, Debugger, and MIDL Compiler Issues

Windbg Cannot Use Visual C++ 5.0 Debugging Information.

_declspec(novtable)

_ATL_MIN_CRT and Link Error "unresolved external symbol _main"

DCOM95 Available for Distributed Applications

/WS:AGGRESSIVE (Aggressively Trim Process Memory)

/FD (Generate File Dependencies)

_MSC_EXTENSIONS Compiler Macro

Option Precedence and the CL Environment Variable

/Zm (Specify Memory Allocation Limit)

Compiler Now Documents Type Library Dependencies

Keywords _emul and _emulu Not Documented

New Linker Error: Linker Tools Error LNK1189

Benefit of Using the Linker's /OPT:ICF Option

Debugging Windows API Functions with NT Symbols Loaded

If Screen Flashes During Build or the Wrong Code Page Is Used When

Debugging a Console Application

Incorrect Documentation for the Clean Menu Command

MIDL2020: error generating type library: save all changes failed

Error RC2104 : undefined keyword or key name: MFT_STRING

Error Command Line Warning MIDL1009:unknown argument ignored

Additional Information on the C2065 Compiler Error

Documentation for Error C2712 Incomplete

Compiler Warning (level 4) C2498

Compiler Warning (level 4) C4238

Compiler Warning (level 3) C4800

Compiler Warning (level 1) C4804

Compiler Warning (level 1) C4805

Compiler Warning (level 1) C4806

Compiler Warning (level 1) C4807

Compiler Warnings (level 1) C4808

Compiler Warning (level 1) C4809

MORE INFORMATION

Windbg Cannot Use Visual C++ 5.0 Debugging Information

Because of changes to the format of debugging information in Visual C++ 5.0, you will not be able to use any version of Windbg prior to 5.0.1719. The Windbg debugger (distributed in the Win32 SDK) to do source level debugging of programs created with Visual C++ 5.0.

_declspec(novtable)

This form of _declspec can be applied to any class declaration, but should only be applied to pure interface classes, i.e. classes that will never be instantiated on their own. The _declspec stops the compiler from generating code to initialize the vfptr in the constructor(s) and destructor of the class. In many cases, this removes the only references to the vtable that are associated with the class and, thus, the linker will remove it. Using this form of _declspec can result in a significant reduction in code size.

_ATL_MIN_CRT and Link Error "unresolved external symbol _main"

When you build a Release version of an ATL project, you can get the following link error:

LIBCMT.LIB(crt0.obj) : error LNK2001: unresolved external symbol _main

This error occurs if you are using CRT functions that require CRT startup code. The Release configuration defines _ATL_MIN_CRT, which excludes CRT startup code from your EXE or DLL.

To avoid this error, do one of the following:

Remove _ATL_MIN_CRT from the list of preprocessor defines to allow CRT startup code to be included. On the Project menu, click Settings. In the Settings For: drop down list, choose Multiple Configurations. In the Select project configuration(s) to modify dialog box that appears, click the check boxes for all Release versions, and then click OK. On the C/C++ tab, choose the General category. Remove _ATL_MIN_CRT from the Preprocessor definitions edit box.

If possible, remove calls to CRT functions that require CRT startup code. Instead, use their Win32 equivalents. For example, use lstrcmp instead of strcmp. Known functions that require CRT startup code are some of the string and floating point functions.

DCOM95 Available for Distributed Applications

The Microsoft Distributed COM (DCOM) files for Windows 95 are useful for creating distributed applications. Some Visual C++ 5.0 samples require DCOM. You can find DCOM95 in the \dcom95 directory on the disc that includes "Microsoft Visual C++" on the label. (Disc 1 if you purchased Visual C++; Disc 3 if you purchased Visual Studio.) Check out the Visual C++ 5.0 Compiler COM support and Active Template Library ( ATL) with DCOM95.

/WS:AGGRESSIVE (Aggressively Trim Process Memory)

Use this linker option to add the WS_AGGRESSIVE attribute to your application's image. The Windows NT 4.0 loader will recognize this attribute and aggressively trim the working set of the process when it is not active. Using this option is similar to adding the following call throughout your application:


   SetProcessWorkingSetSize(hThisProcess, -1, -1)

/WS:AGGRESSIVE can be used for applications that must have a low impact on the system's memory pool.

If the speed of your application is important, do not use /WS:AGGRESSIVE without testing the resulting performance implications. Ideal candidates are processes that tend to operate in the background, such as services and screen savers.

/FD (Generate File Dependencies)

The development environment's build system uses the /FD option to ensure that the most reliable dependency information is used when it builds your project.

_MSC_EXTENSIONS Compiler Macro

This macro is defined unless you compile with /Za for ANSI compatibility. Its value, when defined, is 1.

Option Precedence and the CL Environment Variable

Compiler options are processed "left to right", and when a conflict is detected, the last (right-most) option wins. The CL environment variable is processed before the command line, so in any conflicts between CL and the command line, the command line takes precedence.

/Zm (Specify Memory Allocation Limit)

The compiler uses a number of discrete heaps, each of which has a finite limit. The total of the size limits for all heaps is about 105 MB, but when any one heap is exhausted, the compiler cannot continue. Memory is allocated only as needed; the 105 MB limit is just to keep from using too much memory. Exceeding any one of the discrete-heap size limits occurs only in rare circumstances involving very large or very complex programs. Should your program exceed one of these limits, use /Zm to scale the total size of all the limits. For example, when /Zm200 is specified, the total of all heap size limits is 210MB.

Compiler Now Documents Type Library Dependencies

The compiler provides the full path to any typelib dependency required by the typelib it is currently processing. The path is written, in the form of comments, into the typelib header (.TLH) that the compiler generates for each processed typelib.

If a typelib includes references to types defined in other typelibs, then the .TLH file will include comments of the following sort:


   // 

   // Cross-referenced type libraries:

   // 

   //  #import "c:\path\typelib0.tlb"

   //

The actual filename in the #import comment is the full path of the cross- referenced typelib, as stored in the registry. If you encounter errors that are due to missing type definitions, check the comments at the head of the .TLH to see which dependent typelibs may need to be imported first. Likely errors are syntax errors (e.g. C2143, C2146, C2321), C2501 (missing decl- specifiers), or C2433 ('inline' not permitted on data declaration) while compiling the .TLI file.

You must determine which of the dependency comments are not otherwise provided for by system headers and then provide an #import directive at some point before the #import directive of the dependent typelib in order to resolve the errors.

Keywords _emul and _emulu Not Documented

Syntax:


   _int64 _emul(long, long);


   unsigned _int64 _emulu(unsigned long, unsigned long);

Use these keywords to efficiently multiply two 32-bit integer numbers, which return a 64-bit result.

New Linker Error: Linker Tools Error LNK1189


   LIBTOOMANYMEMBERS:: library limit of number objects exceeded

The limit of 65535 objects or members in a library has been exceeded.

Benefit of Using the Linker's /OPT:ICF Option

The /OPT:ICF[,iterations] option removes identical COMDAT records in order to reduce the size of the executable produced by the linker. The iterations value specifies the number of times to repeat the search for identical COMDAT records. If /OPT:REF is specified, /OPT:ICF is on by default unless you specify /OPT:NOICF as well.

Debugging Windows API functions with NT Symbols Loaded

If you have the NT symbols loaded and you want to debug Windows API functions, you need to enter the decorated name of the function while setting a breakpoint on the function. For example, if you want to set breakpoint on the MessageBeep function, use the decorated name _MessageBeep@4. The decorated name can be obtained in the map file created through linker options.

If Screen Flashes During Build or the Wrong Code Page is used When Debugging a Console Application

If you are using Windows 95, delete any of the following files from your computer:

_DEFAULT.PIF

DEFAULT.PIF

CONAGENT.PIF

These files were used by Windows 3.x, and are not needed by Windows 95. If they are used, while you are debugging a console application, the country settings associated with the PIF files will be used, and could result in the wrong code page being loaded. A result of their use on Windows 95 may be screen flashing during a Build, if you have specified console windows to be full screen.

Incorrect Documentation for the Clean Menu Command

The Clean command is incorrectly documented in the "Remove Intermediate Files" topic as follows:

You can remove all files from the intermediate directories in any
project configuration in your project workspace.

In actuality, the Clean command will not remove precompiled header (.PCH) files. This is by design, as the initial generation of .PCH files is time consuming. If the project is a server project that has been registered on the system, the registry entries will not be cleaned up. The final result of the of using the Clean command is to delete all executable (.EXE), dynamic link library (.DLL), and Control (.OCX) files.

MIDL2020: error generating type library: save all changes failed

This error can result if the path to the .IDL file is longer than 126 characters, which is because oleaut32.dll does not currently support path names that are greater than 126 characters. The workaround is to reduce the path to the .IDL file so that it is less than 126 characters.

Error RC2104 : undefined keyword or key name: MFT_STRING

If you encounter this error, open MCL\MFC\Include\AfxRes.h and add the following include directive:


   #include <winresrc.h>

Error Command Line Warning MIDL1009 : unknown argument ignored

MIDL.exe version 3.01.75 generates this error if its arguments are passed in a response file and one of the arguments is an MBCS-character file name that contains a space.

Workarounds:

Use a batch file to invoke MIDL with its arguments.

Delete the space from the MBCS file name.

Additional Information on the C2065 Compiler Error

The following information belongs in the tips section of the C2065 compiler error:

Make sure you're using proper namespace scope. For example, in order to properly resolve ANSI C++ Standard Library functions and operators, you must state that you're using the std namespace with the using directive.

For example, unless the using directive is uncommented, the following sample will fail to compile because the cout stream is defined in the std namespace:


   #include <iostream>

   // using namespace std;

   void main()

   {
     cout << "Hello" >> endl;
   }

Documentation for Error C2712 Incomplete

The documentation for this error should also contain the following information:

The error can be avoided when using the /GX option by not having local variables or parameters with types that have destructors in a function that uses structured exception handling (SEH). Furthermore, SEH cannot be used in constructors or destructors if using /GX. Code that requires SEH can also be moved to another function in order to avoid the error.

Compiler Warning C2498

C2498 : "%$S' 'novtable' can only be applied to class declarations"

For example, using __declspec(novtable) with a function, as follows, is illegal:


   void __declspec(novtable) f() {
   }

Compiler Warning (level 4) C4238

nonstandard extension used : class rvalue used as lvalue

This error occurs when you are using Microsoft language extensions (/Ze) and use a class type as is an rvalue in a context that implicitly or explicitly takes its address. For example:


   struct C
   {
     C();
   };

   C * pC = &C(); // yields C4238

This usage is not permitted by the C++ Working Paper, and in some cases (such as the example above) can be quite dangerous. This usage is being permitted under /Ze for compatibility with previous versions of the compiler, which did not flag this error. This usage is not permitted under /Za.

Compiler Warning (level 3) C4800

'type' : forcing value to bool 'true' or 'false' (performance warning)

This warning is generated when some non-bool value is assigned or coerced into type bool. Typically, this message is caused by assigning int variables to bool variables where the int variable contains only values true and false, and could be redeclared as type bool. If you can't rewrite the expression to use type bool, then you can add "!=0" to the expression, which gives the expression type bool. Casting the expression to type bool will not disable the warning, which is by design.

Compiler Warning (level 1) C4804

'%$L' : unsafe use of type 'bool' in operation

This warning is for unary operations and is generated when you used a bool variable or value in an unexpected way. For example, if you use operators such as the negative unary operator (-) or the complement operator (~).

Compiler Warning (level 1) C4805

'%$L' : unsafe mix of type 'type' and type 'type' in operation

This message is similar to C4804, and it is limited to binary operations. It is generated for operations such as b &= i, b+=i, b/=b, b%=i, etc., where b and i are bool and int respectively .

Compiler Warning (level 1) C4806

'%$L' : unsafe operation: no value of type 'type' promoted to type
'type' can equal the given constant

This message warns against serious errors such as b == 3, where b has type bool. The promotion rules cause bool to be promoted to int. This is legal according to the ANSI C++ Working Paper, but it can never be true.

Compiler Warning (level 1) C4807

'%$L' : unsafe mix of type 'type' and signed bitfield of type 'type'

This warning is generated when comparing a one-bit signed bit field to a bool variable. Since a one-bit signed bit field can only contain the values -1 or 0, it is dangerous to compare it to bool. No warnings are generated about mixing bool and one-bit unsigned bitfields since they are identical to bool and can only hold 0 or 1.

Compiler Warnings (level 1) C4808

case '%d' is not a valid value for switch condition of type 'bool'

This warning occurs if a switch condition is of type bool and one of the case values is outside the range of bool (that is, true and false). Only true, false, 1, 0, and default are valid case values if the switch condition is of type bool.

Compiler Warning (level 1) C4809

switch statement has redundant 'default' label; all possible 'case'
labels are given

This message is generated in places where you have both 'true' and 'false' cases in addition to a default label.

Keywords :
Version : winnt:5.0
Platform : winnt
Issue type :