Re: [Dev-C++] Crash with macro to template conversion

[Per W. <pw...@ia...>]

First of all - your create template function is declared to return void,
so why do you end it with return ptr?

Second, you send in a T* ptr parameter. Note that since C++ uses
call-by-value, this will behave like a lokal variable, i.e any assign to
ptr will not reflect back to the caller. You should change the first
parameter of create to be a reference to a pointer. That way, the assign
to ptr will reflect back to the variable obj of the caller.

/Per W

On Fri, 27 Feb 2004, David McKen wrote:

> Ok here is my problem.
>
> I want to replace:
> #define CREATE(result, type, number)                \
> do                              \
> {                               \
>     if (!((result) = (type *) calloc ((number), sizeof(type)))) \
>     {                               \
>     perror("malloc failure");               \
>     fprintf(stderr, "Malloc failure @ %s:%d\n", __FILE__, __LINE__ );
> \
>     abort();                        \
>     }                               \
> } while(0)
>
> With it's C++ equivalent.
>
> So far I have:
> #define CREATE(result, type, num)   = create<type>((result),(num))
> template<class T>
> void create(T * ptr, int number, char * f_name = __FILE__, int l_num
> =
> __LINE__)
> {
>   try {
>     ptr = new T[number];
>   }
>   catch(bad_alloc& b)
>   {
>     perror("malloc failure");
>     fprintf( stderr, "Malloc failure @ %s:%d\n", f_name, l_num );
>     abort();
>   }
>   if ( !ptr )
>   {
>     perror("malloc failure");
>     fprintf( stderr, "Malloc failure @ %s:%d\n", f_name, l_num );
>     abort();
>   }
>   return ptr;
> }
>
> But the program crashes after the function call when any attempt to
> acces
> the data occours:
> e.g.
> OBJ_DATA * obj;
> CREATE( obj , OBJ_DATA, 1 );
>
> obj->some_field = 5; //Crashes here and obj = 0x0 from gdb.
>
> Thanks in Advance
> David McKen
>
>
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