Problem on mixing C and C++ with a const struct (GCC compiler)

[slaindevil]

Hey ppl,

I got a little problem :/

I got the following C code in a header file and I am not allowed to change it:

const structTemp tmp = {.x = 5};

The code just works fine for GCC.

Now I got a project made with the Eclipse IDE in C++. And I am linking to the header file. Then I get the following error:
"expected primary-expression before '.' token"

What can I do to handle this problem? :(
I just tried to make a extern "C" {} around the header, but it does not work :(

Anyone got some help for me? :(

Greets

[arnaudk]

I don't believe you. Firstly, because you are omitting the keyword 'struct': in C++, you are allowed to omit the struct keyword, but then you compile it with a C++ compiler like g++ not a C compiler like gcc.

Secondly, because this is not standard C or C++ syntax. You initialize a struct thus:

struct structTemp 
{
  int x;
  char c;
}; // definition
 
structTemp tmp1 = {5,'A'};        // initialization (in C++)
struct structTemp tmp2 = {5,'A'}; // initialization (in C/C++)
struct structTemp tmp3;           // delcaration (C/C++)
tmp3.x = 5;                       // initialization
tmp3.c = 'A';
 

[slaindevil]

The struct is defined by something like:
SORRY, I now found the correct definition, and its not only struct, it looks like this:

typedef union
{
    struct
    {
         int h;
         int l;
    } x1;
    unsigned int x;
} structTemp;
 

Then I got this code

const structTemp tmp = {.x = 5};

It compiles great with

gcc main.c -o main

where main.c links the header file with all this code in it.

When I link the header into my Eclipse project C++ code, I got the error from my first post.

[arnaudk]

In that case the answer is simple: while some C compilers support this method of initializing unions, pre-C99 and C++ does not. You'll have to use assignment instead of initialization.

[slaindevil]

In that case the answer is simple: while some C compilers support this method of initializing unions, pre-C99 and C++ does not. You'll have to use assignment instead of initialization.

Damn :( Ok, thanks :(

And how to assign a const variable? :(

[Banfa]

You can't assign to a const variable, only initialise it but you could initialise in either of these 2 ways to get the same effect as your original code that is usable everywhere.

const structTemp tmp = {5, 0};
 
const structTemp tmp = {5};
 

[slaindevil]

You can't assign to a const variable, only initialise it but you could initialise in either of these 2 ways to get the same effect as your original code that is usable everywhere.

const structTemp tmp = {5, 0};
 
const structTemp tmp = {5};
 

Yeah, thats a good idea. Ill do it this way.

But when the structTemp looks like this:

typedef union
{    
           struct    
           {    
                int h;    
                int l;    
           } x1;    
           unsigned int x;    
} structTemp;
 

Wouldnt be

const structTemp tmp = {0, 5};

be the right way?

I know they are union, but how should the compiler know, that the 5 is meant for variable x?

Greets,

Edit:
And what how could I initialize x1.h and x1.l?

Edit2:
Ok, I tried it out by myself:
const structTemp tmp = {5}; is right for making x = 5.
And:
const structTemp tmp = {{10, 5}}; is right for making h = 10 and l = 5.

Thx anyway :)

[slaindevil]

Ok, one last question about mixing C and C++.

If I got a variable called "delete" in my C code, is there a way to make the C++ ignore it?

Its C, but the C++ Compiler gives me an error cos delete is a keyword in C++.
With extern "C" {}; I can't solve the problem :(

[Banfa]

If I got a variable called "delete" in my C code, is there a way to make the C++ ignore it?

If it is C then compile it with a C compiler.

If it is C++ then you can't use the keyword delete as a variable name.

If you are using a C++ compiler to compile it then it isn't C although it might be code that is compatible with both C and C++ compilers, which is in fact a subset of both languages which still would include not using C++ keywords as variable names.

[slaindevil]

If it is C then compile it with a C compiler.

If it is C++ then you can't use the keyword delete as a variable name.

If you are using a C++ compiler to compile it then it isn't C although it might be code that is compatible with both C and C++ compilers, which is in fact a subset of both languages which still would include not using C++ keywords as variable names.

Ok. Then I have to rename it. Thanks!