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

• The Microsoft C/C++ Compiler (CL.EXE) included with: - Microsoft C/C++ for MS-DOS, version 7.0 - Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51, 1.52 - Microsoft Visual C++, 32-bit Edition, versions 1.0, 2.0, 2.1, 4.0,

       4.1, 4.2, 5.0
  

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

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));