重载运算符时返回的堆栈地址 memory []

Question

I'm encountering some issues with overloading the [] operator for a problem in class. This is the function for the overloading:

const char* Person::operator[](const char* str)
{
    if (strcmp(str, "name") == 0)
        return reinterpret_cast<const char *>atoi(name);

    if (strcmp(str, "age") == 0)
    {
        char temp[4];
        _itoa(age, temp, 10);
        //cout << temp;
        return temp;
    }
}

The class defition looks like this

class Person
{
private:
    const char* name;
    unsigned int age;
    double height;
    int gradeNo;
    int grades[10];
public:
    Person();
    Person(const char* name, int age, double height);
    void addGrade(int grade);
    const char* operator [] (const char* str);
    operator int();
};

The problem I'm getting is with the return temp; line from the operator overload function. CLion returns the following warning: Address of stack memory associated with local variable 'temp' returned

Sure enough, when trying to use the operator, the value returned is a memory address. How can I go about fixing this? Is it related to the return type of the function?

Answer 1

You are taking an address to a temporary (that is located on the stack), that will leave the returned pointer dangling almost immediately.

I would very strongly suggest using std::string for strings, do not write C++ just as C with classes.

Then return by std::string by value here. Bad C-like alternative is to allocate the string on the heap and return that, preferably as std::unique_ptr at least.

EDIT after the comment below:

Since you are required to convert an integer to string and return the value, you cannot return a temporary variable, the result must outlive the method. There are basically two bad options:

1. Make temp static, this way the pointer remains valid. Downside is the function is no longer re-entrant. This is safer because it won't leak.

const char* foo(int age){
    static char temp[4];
    _itoa(age, temp, 10);
    return temp;
}

2. Return a heap allocated string. Big danger is that you are leaving the user to deallocate it:

const char* foo(int age){
    char* temp = new char[256];
    _itoa(age, temp, 10);
    return temp;
}

I believe you also have a typo in your code:

return reinterpret_cast<const char *>atoi(name);

The atoi should not be there, right? reinterpret_cast should not be needed.