更改const char指针的问题

Question

I'm having some issues with changing a char pointer and can't figure out where I'm going wrong

Here's my function for changing the description...

void appointment::changeDescription(const char * s)   //  change an existing description
{

if (desc != NULL)
    strcpy(desc, s);

if (s == NULL)
    return;

}

And here's the function that calls the change description function.

bool  keyBoardEnterAppointment( schedule & sched)  // return true if successful
// return false if full
{
    if (sched.isFull() == true)
    {
        cout << "Schedule is FULL." << endl;
        return false;
    }
    else
    {
    appointment s;
    int day, month, year;
    char *desc = new char;
    long source;

    cout << "*/Enter Appointment\\* ";
    cout << "Description: "; cin >> desc;
    cout << "Source: "; cin >> source;

    cout << "Month: "; cin >> month;
    cout << "Day: "; cin >> day;
    cout << "Year: "; cin >> year;

    s.changeDescription(desc);
    s.setSource(source);
    s.setDay(day);
    s.setMonth(month);
    s.setYear(year);
    sched.addtoSchedule(s);

    sched.print(cout);

    return true;
}

}

It compiles and runs but the description remains the same as the default constructor description...

Answer 1

If you use std::string to store the description in the appointment class then you can make things much easier for yourself and for the people who end up working on your code. The changeDescription method would then become this:

#include <string>

void appointment::changeDescription(std::string const& s){
    this->desc = s;
}

And change the calling code to this:

std::string desc;

Then all of the annoying memory management that causes the problems you are facing are fixed pretty much for free (in terms of programming effort that is). Generally speaking this is considered to be better idiomatic c++ code than using null terminated C-style char arrays.

Another thing about your code is that you really should check that s is not null before you try to copy it, not afterwards.