Q93401: PRB: C2279: Braces Not Valid in Function Default Argument List

Article: Q93401
Product(s): Microsoft C Compiler
Version(s): 1.0,1.5,1.51,1.52,2.0,2.1,4.0,4.1,4.2,5.0,6.0
Operating System(s): 
Keyword(s): kbCompiler kbCPPonly kbVC100 kbVC150 kbVC151 kbVC152 kbVC200 kbVC210 kbVC400 kbVC410 kb
Last Modified: 17-APR-2002

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The information in this article applies to:

- Microsoft C/C++ for MS-DOS 
- Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5, 1.51, 1.52 
- Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 4.0, 4.1, 4.2, 5.0, 6.0 
- Microsoft Visual C++.NET (2002) 
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SYMPTOMS
========

When Microsoft C/C++ compiles an application that specifies a structure in the
default arguments for a function, the compilation fails with the following error
messages:

  error C2059: syntax error : '{'
  error C2279: cannot use braces to initialize default arguments

If you are using Visual C++ .NET compiler, the following compiler errors will be
generated instead of the above two compiler errors.

  error C2143: syntax error : missing ')' before '{'
  error C2059: syntax error : ')'

CAUSE
=====

According to the C++ grammar, the default value for an argument must be an
expression. An initializer list, such as that used to initialize a structure, is
not an expression.

RESOLUTION
==========

Define a constructor to perform the required initialization.

MORE INFORMATION
================

The first code example demonstrates the errors listed above. The second code
example demonstrates the correct method to initialize the structure.

Code Sample 1
-------------

  /*
   * Compile options needed: /c
   */ 

  struct ag_type
  {
     int a;
     float b;
  };

  void func(ag_type arg = {5, 7.0});

Code Sample 2
-------------

  /*
   * Compile options needed: /c
   */ 

  struct ag_type
  {
     int a;
     float b;
     ag_type(int aa, float bb) : a(aa), b(bb) {}
  };

  void func(ag_type arg = ag_type(5, 7.0));

Additional query words: 8.00 8.00c 9.00 9.10

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Keywords          : kbCompiler kbCPPonly kbVC100 kbVC150 kbVC151 kbVC152 kbVC200 kbVC210 kbVC400 kbVC410 kbVC420 kbVC500 kbVC600 
Technology        : kbVCsearch kbVC400 kbAudDeveloper kbZNotKeyword8 kbvc150 kbvc100 kbZNotKeyword3 kbVC410 kbVC420 kbVC500 kbVC600 kbVC151 kbVC200 kbVC210 kbVC32bitSearch kbVC16bitSearch kbVC152 kbVCNET kbVC500Search
Version           : :1.0,1.5,1.51,1.52,2.0,2.1,4.0,4.1,4.2,5.0,6.0
Issue type        : kbprb

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