Article: Q64686
Product(s): Microsoft C Compiler
Version(s): 1.0,1.5,2.0,4.0,4.1,4.2,5.0,6.0
Operating System(s):
Keyword(s): kbcode kbCompiler kbVC100 kbVC150 kbVC200 kbVC400 kbVC410 kbVC420 kbVC500 kbVC600
Last Modified: 27-NOV-2001
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The information in this article applies to:
- Microsoft C for MS-DOS
- Microsoft C for OS/2
- Microsoft C/C++ for MS-DOS
- Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5
- Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 4.0, 4.1, 4.2, 5.0, 6.0
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SYMPTOMS
========
In Microsoft C, using a nameless structure as a member of a structure causes a
compiler error if the two structures both have members with the same name. C
versions 6.x generate the error:
C2030: 'varname': struct/union member redefinition.
In C/C++ versions 7.0 and later, the error is:
error C2020: 'varname' : 'struct' member redefinition
The code sample below, when built as a C source file, reproduces the error. The
same sample, built as a C++ source file, will not display this behavior.
CAUSE
=====
This is expected behavior, not a bug. When a nameless structure is used within
another structure, the members of the nameless structure become members of the
new structure. In the C language, the member names must be unique.
MORE INFORMATION
================
Sample Code
-----------
/* compile options needed: none /Tc */
void main(void)
{
struct s1
{
int a,b,c;
};
struct s2
{
struct s1; /* nameless struct */
float z;
char a[10]; /* error occurs here */
} *p_s2;
}
The second structure (s2) is effectively the following:
struct s2
{
int a,b,c; /* Was nameless struct s1 */
float z;
char a[10]; /* Error occurs here */
} *p_s2;
This illustrates that the member variable "a" is being redefined. Correctly used
nameless structures can provide a good technique for building structures with
similar data structure without having the complexity of truly nested structures.
Additional query words: 8.0 8.0c 9.0 10.0 11.0 /Tp
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Keywords : kbcode kbCompiler kbVC100 kbVC150 kbVC200 kbVC400 kbVC410 kbVC420 kbVC500 kbVC600
Technology : kbVCsearch kbVC400 kbAudDeveloper kbZNotKeyword8 kbvc150 kbvc100 kbCCompSearch kbZNotKeyword3 kbVC410 kbVC420 kbVC500 kbVC600 kbVC200 kbVC32bitSearch kbVC16bitSearch kbVC500Search
Version : :1.0,1.5,2.0,4.0,4.1,4.2,5.0,6.0
Issue type : kbprb
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