How to free memory in this operator overloading definition?

[Liang]

This is the declaration of a class called String.

// string1.h -- fixed and augmented string class definition
#include <iostream>
using std::ostream;
using std::istream;

#ifndef STRING1_H_
#define STRING1_H_
class String
{
    private:
        char * str;             // pointer to string
        int len;                // length of string
        static int num_strings; // number of objects
        static const int CINLIM = 80;  // cin input limit
    public:
        // constructors and other methods
        String(const char * s); // constructor
        String();               // default constructor
        String(const String &); // copy constructor
        ~String();              // destructor
        int length () const { return len; }
        void stringlow();
        void stringup();
        int has(char c) const;
        // overloaded operator methods    
        String & operator=(const String &);
        String & operator=(const char *);
        char & operator[](int i);
        const char & operator[](int i) const;
        // overloaded operator friends
        friend bool operator<(const String &st, const String &st2);
        friend bool operator>(const String &st1, const String &st2);
        friend bool operator==(const String &st, const String &st2);
        friend ostream & operator<<(ostream & os, const String & st);
        friend istream & operator>>(istream & is, String & st);
        friend const String operator+(const String& st1, const String& st2);
        // static function
        static int HowMany();
};
#endif

This is the definition of the overloaded + operator, where I must use new to allocate the memory. However, there seems no place I can use a delete to free the memory pointed by ps.

String operator+(const String & s1, const String & s2)
{
    int len = s1.chars + s2.chars;
    char * ps = new char [len + 1];
    std::strcpy(ps, s1.str);
    std::strcat(ps, s2.str);
    String temp(ps);
    return temp;
}

[kbw]

String operator+(const String & s1, const String & s2)
{
    int len = s1.chars + s2.chars;
    char * ps = new char [len + 1];
    strcpy(ps, s1.str);
    strcat(ps, s2.str);
    String temp(ps);
    delete [] ps, ps = 0;
    return temp;
}

[Liang]

Thanks.
Does the ps=0 statement set the ps pointer to NULL? Is it necessary to do so?

[kbw]

Yes, it sets ps to null. It isn't necessary to do so in this case, but if you weren't returning immediately it would be. I do it instinctively.