如何将 char* 复制到另一个 char* 并释放第一个而不影响第二个

Question

My code is below. Initially it showed an error that a same memory location is being freed twice.ie Returned object temp is freed twice(while return and after copied to obj2). So, i overloaded the copy constructor to have different memory while coping. Then error disappeared but a garbage value was stored in obj2 instead of "ll". Then I overloaded the = operator void main line 2 from shallow to deep copy. Now garbage value is gone but it has a null value instead of "ll".I don't want to comment free() or use any functions from #include.Can someone say what should do?.

class CustomStringClass 
{
    private:
        char* Input;
   
    public:
        CustomStringClass (string Input){
          //Dynamic mem allocation done to char*Input and store the input
        }
    
        CustomStringClass Substring(int Start, int End){
          //Substring found as "ll" from "Hello"
          CustomStringClass temp("ll");
          return temp;
        }
    
        ~CustomStringClass(){
            free(this->Input);
         }
};

void main()
{

    CustomStringClass Obj1("Hello");
    CustomStringClass Obj2=Obj1.Substirng(2,3);

}

Answer 1

You need to allocate new memory and shift it to use a raw char array of unknown length.

Also it's a common recommendation not to use "using namespace std", and a personal recommendation to use the same name for function arguments and member function, having to remember to use this-> correctly is just asking for trouble.

//Also use references note to make unnecessary copies
CustomStringClass (const std::string& letsUseADifferentName){
    Input = new char[letsUseADifferentName.Length()];
    memcpy(Input, letsUseADifferentName.c_str(),  letsUseADifferentName.Length());
}

~CustomStringClass(){
    delete[] Input;
}

Since you are using a pointer as a class member, you need to write your own copy and move semantics, for that to work correctly.

This is to use functions like

CustomStringClass a;
CustomStringClass b = a;
CustomStringClass c(b);
///etc

There's a lot of good posts and videos on move semantics. Pick one that vibes with you.