INFO: Pointer to Undeclared Structure Does Not Generate Error

• The Microsoft C/C++ Compiler (CL.EXE) included with: - Microsoft C for MS-DOS, versions 5.1, 6.0, 6.0a, 6.0ax - Microsoft C for OS/2, versions 5.1, 6.0, 6.0a - Microsoft C/C++ for MS-DOS, version 7.0 - Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51 - Microsoft Visual C++ 32-bit Edition, versions 1.0, 2.0, 2.1, 4.0, 5.0

SUMMARY

Code that declares a pointer to a nonexistent structure compiles without warning or error. This is correct behavior.

Note that dereferencing a pointer to an undefined structure, or attempting to use a field, will produce errors. In general, you are allowed to make a reference to an undefined struct as long as the operation doesn't need to know the size of that struct or the names of its fields. This method of declaration is commonly used in linked lists.

Sample Code

   void main (void)
   {
      struct non_existent *ptr;         // legal
      struct x
      {
       struct x *previous;      // legal, note that struct x is
       struct x *next;          // not yet defined
      };
   }