How to read multiple structs from a binary file - c++

Question

I have written two instances ck1,ck2 of a struct named Cookie and have saved them in a binary file named "mydat" by calling a function :
bool s_cookie(Cookie myck,std::string fname) {
std::ofstream ofs(fname,std::ios::binary | std::ios::app);
if(!ofs) return false;
ofs.write((char *) &myck, sizeof(Cookie));
ofs.close();
return true;
}
of course myck can be ck1, ck2, etc, and fname reps the "mydat" binary file. So the two structs have both been saved in the same file.
Now I want to read them back into ck3 and ck4 respectively. How do i do that? Cookie looks like this :
struct Cookie {
std::string name;
std::string value;
unsigned short duration;
bool expired;
};
Thanks

Answer 1

Something like writing, but read them, if Cookie is a POD:
std::ifstream ifs(fname,std::ios::binary);
Cookie ck3, ck4;
ifs.read((char *) &ck3, sizeof(Cookie));
ifs.read((char *) &ck4, sizeof(Cookie));
Also, you should check the result of each opening and reading operation and handle them.
Update: After your update and seeing the Cookie, you can not simply write it into a file. You should serialize it or make a well-defined protocol to read/write data.
A simple workaround is (read the comment):
// Assume name and value are not longer that 99
// and you don't care about wasted space in the file
struct CookiePOD {
CookiePOD(const Cookie &p)
{
// I ignored bound checking !
std::copy(p.name.begin(), p.name.end(), name);
name[p.name.size()] = 0;
std::copy(p.value.begin(), p.value.end(), value);
value[p.value.size()] = 0;
duration = p.duration;
expired = p.expired;
}
char name[100];
char value[100];
unsigned short duration;
bool expired;
};
And then try to read/write CookiePOD instead of Cookie.