CODEWITHSUNDEEP
c++11new-operator
Rajesh
Rajesh

Reputation: 1135

How Memory is allocated for member in the example

I was looking at Microsoft site about single inheritance. In the example given (code is copied at the end), I am not sure how memory is allocated to Name. Memory is allocated for 10 objects. But Name is a pointer member of the class. I guess I can assign constant string something like 

DocLib[i]->Name = "Hello";

But we cannot change this string. In such situation, do I need allocate memory to even Name using new operator in the same for loop something like 

DocLib[i]->Name = new char[50];

The code from Microsoft site is here:

// deriv_SingleInheritance4.cpp  
// compile with: /W3  
struct Document {  
   char *Name;  
   void PrintNameOf() {}  
};  

class PaperbackBook : public Document {};  

int main() {  
   Document * DocLib[10];   // Library of ten documents.  
   for (int i = 0 ; i < 10 ; i++)  
      DocLib[i] = new Document;  
}

Upvotes: 0

Views: 36

Answers (1)

mman
mman

Reputation: 89

Yes in short. Name is just a pointer to a char (or char array). The structure instantiation does not allocate space for this char (or array). You have to allocate space, and make the pointer(Name) point to that space. In the following case

DocLib[i]->Name = "Hello";

the memory (for "Hello") is allocated in the read only data section of the executable(on load) and your pointer just points to this location. Thats why its not modifiable.

Alternatively you could use string objects instead of char pointers.

Upvotes: 2

Related Questions