Question

I have problem with void * I want to put what contain in a string to output it,I know that in compiling moment the compiler doesn’t know what the pointer point to so I think to use a kind of cast(cast the *(void*) to string ) the static_cast:

  std::string get_Info_Field (std::string nameTab,int IDF)   

  {     ostringstream os;
        iter=Inst_Data.find(nameTab);

        if(iter!= Inst_Data.end())
        {   iterF=(iter->second).find(IDF);
            if(iterF!=(iter->second).end())
                    {os<<*static_cast<std::string*>(iterF->second.value);}
            else    { os<<""; }
        }
        else {  os<<"";}

    return os.str();
};

here iterF->second.value is a void* that I want to get its value that can point to any type(int,string,float,long,char..), my question is :is that safe? will return the right value of the pointer whatever the type ? I tested with int it works but I’am not sure for the rest.

please any help will be appreciated.

Answer 1

You can’t safely cast an pointer to an arbitrary value to a string and expect something sensible to happen; at absolute minimum you also need to know the size of the thing pointed to, and you may also need to watch out for embedded NULs and the like. If you know that it is always a std::string then you can cast to a std::string safely; but you do have to know with certainty, or you’re courting a core dump or random output.