I want to make an agenda-type program in which I can save my contacts in a .bin file. The problem is that when I run the crashea program.
This is the part that reads the .bin:
ifstream entrada;
entrada.open(Archivo,ios::binary);
Contacto c;
while(entrada.read((char*)&c,sizeof(Contacto))){
c.Print();
}
entrada.close();
Where Archivo is a constant that saves the name of the file: contactos.dat
while(entrada.read((char*)&c,sizeof(Contacto)))
// ^^^^^^^^^
If% co_of% results from using, directly or indirectly, dynamic memory that reading will fail you. why? Because then you will copy pointers instead of the values that interest you.
An example:
class Prueba {
int* datos;
};
int main ()
{
std::cout << sizeof(Prueba);
}
The following program will print 4 or 8 depending on whether you compile it in 32 bits or 64 ... regardless of what you have stored in Contacto .
If you take and dump datos to a file so rough, what you're going to do is save only the value of the pointer ... so if Prueba points to a list of 20 elements located in datos , 0x102030 will be stored in the file. Note that the data is not being saved, then when the program is closed the data will be lost forever ...
and why does the program crack?
Because you are overwriting the pointers causing them to point to invalid positions.
If, in the previous example, you read the file and save its contents in an object of 0x102030 , what you will get is that Prueba points to datos ... it is easy to guess that memory does not it belongs to your application, so the operating system protects and kills your application with the sole purpose of preventing it from corrupting the memory.
What you have to do is save the members of your object manually ... one by one ... the mechanism you describe is only valid if you avoid dynamic memory:
struct Funciona
{
int var1;
char var2 [100];
};
struct NoFunciona
{
int var1;
char *var2; // un puntero!!!!
std::string var3; // string usa internamente punteros!!!
};
Since you did not put the declaration of 0x102030 it is impossible to give you more information