Reinterpret cast can fail on a structure with char array inside it =

[tonnot]

I have the typical code to save a structure .

const char* buffer;
  buffer = reinterpret_cast<const char*> (&value);}

const char* buffer;
  buffer = reinterpret_cast<const char*> (&value);}

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It fails when the structure (value) I pass to it has a fixed char array inside it (in example char title[200]).
Any idea ?

[mcosta]

post an example code please

[tonnot]

Thanks Here you are

struct W__header {
    int          number; 
    char          title [200];
    double       inicial, final;
    int           num;
    float         interval;
};

struct W__header {
    int          number; 
    char          title [200];
    double       inicial, final;
    int           num;
    float         interval;
};

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To set the title I have ( I think here is the problem :

void set_title(std::string txt) {
   strncpy(title,texto.c_str(),200) ;  }

void set_title(std::string txt) {
   strncpy(title,texto.c_str(),200) ;  }

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And my 'put' function :

template <class TTput_stream>
void W_inpout::W_stream::put (TTput_stream &value) {    
                 loc+= sizeof value;                   it works fine
                 lof=loc;
                 const char * buffer ;
                 buffer = reinterpret_cast<const char*> (&value);
}

template <class TTput_stream>
void W_inpout::W_stream::put (TTput_stream &value) {    
                 loc+= sizeof value;                   it works fine
                 lof=loc;
                 const char * buffer ;
                 buffer = reinterpret_cast<const char*> (&value);
}

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I user put(my_class->header);

The buffer and the function works fine with my other structures.
At debugger I see title filled with the std::text passed to ser_title an a lot of \0 until the end of var

Maybe reinterpret_cast does not work becase the structure has the char 'title' inside it ?


Any help would be appreciated.

[tonnot]

I have fix the problem.

If you want a generic function so save to a byte array any class using templates, you cannot use std:string inside your classes, because inside this generic type template function you cannot know the real size of the class you want to store.

That is to say, if you want to use std::string into a class, you need a custom function to can compute the size of the string and so, can to know the right number of bytes of your instance.

So, you have to use char[] and strcpy the std::string to the char . Its a pitty, because then you need to include stdio.h.

Good weekend