Overloading istream operator with dynamic memory allocation

Question

Hello so I am confused with my istream& operator>>. I have to overload this operator to take input for a class that is using dynamic memory allocation for a C string.

My Employee.h file is

#include <iostream>
using namespace std;

const double MIN_WAGE = 10.25;

class Employee {

int num;
char * name;
double rate;

public:

Employee();
Employee(const Employee&);
Employee operator=(const Employee&);
friend istream& operator>>(istream& is, Employee& employee);
friend ostream& operator<<(ostream& is, const Employee& employee);
friend bool operator>(const Employee& a, const Employee& b);
~Employee();
};

I have a copy constructor which called the assignment operator

Employee::Employee(const Employee & e) {

name = NULL;

*this = e;
}

Employee Employee::operator=(const Employee & e) {

if (this != e) {

    num = e.num;
    rate = e.rate;

    if (name != NULL) delete [] name;

    if (e.name != NULL) {
        name = new char[strlen(e.name) + 1];
        strcpy(name, e.name);
    }

    else name = NULL;
}

return *this;

}

And in the assignment operator I have dynamically assigned memory for the length of the C string I am using. My istream function so far:

istream& operator>>(istream& is, Employee & e) {

int n;
double r;
}

My question is: how do I use the new dynamic memory allocation in my assignment operator in my istream function?

score 2 · Answer 1 · answered Mar 14 '13 at 01:50

2

Just change the name data member of class Employee from const char* to std::string and you will not need to override operator= anymore :)

Note that it's a good practice to avoid dynamic allocation as much as possible. Try to take advantage of using objects with automatic storage duration and learn more about RAII idiom. Your code will become easier to read and less vulnerable for memory leaks :)

answered Mar 14 '13 at 01:50

LihO

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Unfortunately I can't just use std::string I have to use c string in this case as well as use dynamic allocation. – user2140629 Mar 14 '13 at 01:59

score 0 · Accepted Answer · answered Mar 14 '13 at 02:09

0

Disclaimer: both solution are for educational purpose and I would not recommend to use it in any real program. If you need to solve homework with strict requirements, then that maybe ok:

First:

istream& operator>>(istream& is, Employee & e) {
    Employee tmp;
    tmp.name = new char[1024];
    is >> tmp.num >> tmp.rate >> tmp.name;
    e = tmp;
    return is;
}

Second - more ugly and more "effective" solution:

istream& operator>>(istream& is, Employee & e) {
    char buffer[1024];
    Employee tmp;
    tmp.name = buffer;
    is >> tmp.num >> tmp.rate >> tmp.name;
    e = tmp;
    tmp.name = 0;
    return is;
}

Again both solution created under condition "to use existing assignment operator", real code should be different.

Note:

if (name != NULL) delete [] name;

is redundant, write

delete [] name;

instead

answered Mar 14 '13 at 02:09

Slava

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So basically its ignoring the dynamic allocation and just making a char array of 1024? – user2140629 Mar 14 '13 at 02:13
No it is using your dynamic allocation as there is assignment operator. If you need just another dynamic allocation, not in your assignment operator, make your question more clear. Anyway to input name from stream you need to provide big enough buffer. – Slava Mar 14 '13 at 02:16
What about deleting the new memory allocation that you created in the istream function? – user2140629 Mar 14 '13 at 02:18
That will be deleted in ~Employee() for object tmp. I suppose you do call delete[] there? Why do you think I added line tmp.name = 0; in second example? – Slava Mar 14 '13 at 02:20
Oh ok forgot about the destructor – user2140629 Mar 14 '13 at 02:22
That's worst thing you can do when working with dynamic allocation - to forget about destructors :) – Slava Mar 14 '13 at 02:24

Overloading istream operator with dynamic memory allocation

2 Answers2