C struct with same type name as variable name?

Question

I am working on a project where there is a .h file that contains the following lines:

File1.h

typedef struct {
int a; 
} MyData;

typedef struct {
  MyData MyData;
} MyDataContainer; 

This is compiled using gnu99 standard without any issues. However, if i include File1.h in a C++ file compiled using gcc standard gnu++17, i get errors related to the type name MyData and the instance MyData having the same name. I am not really used to working in C. Is there a reason to have the same type name as the instance name? I cannot change the C file, are there workarounds to #include File1.h in a C++ file?

Thank you in advance for your help.

File1.h compiles with no errors. When i link the library compiled using gnu99 in a library compiled in C++, it throws errors.

Answer 1

Preamble: In C++, the code in the question is ill-formed, no diagnostic required; see Variable with same name as type - which compiler is right? for Standard references.

---

If you cannot modify the C file then there are no seamless, well-defined workarounds .

It may be possible to disable the error message, in which case the behaviour of the program will be formally undefined, but is likely to work correctly:

• in g++ 13, use -Wno-changes-meaning.
• use -fms-extensions, but that has other effects.

---

Failing that, you will have to make an intermediate layer between the C code and the C++ code, with a new function to wrap every C function the C++ code needed to call with a MyData argument; for example:

// MyKludge.h
typedef struct {
  Type1 myVar1;
  Type2 myVar2;
} MyData;

typedef struct {
    MyData foo;
    TypeA myVarA; 
    TypeB myVarB; 
} MyDataContainer2; 

void File1Func(MyDataContainer2 *x);

// MyKludge.c
#include "File1.h"
#include "MyKludge.h"

void File1FuncWrapper (MyDataContainer2 *x)
{
    // Technically undefined behaviour but will probably work
    File1Func( (MyDataContainer *)x );

    // Definitely well-defined but could be inefficient depending on compiler
    MyDataContainer y;
    y.MyData = x->foo;
    y.MyVarA = x->MyVarA;
    y.MyVarB = x->MyVarB;
    File1Func( &y );
    x->foo = y.MyData;   // If func might change object
    x->MyVarA = y.MyVarA;
    x->MyVarB = y.MyVarB;
}