动态内存分配-C ++

Question

I'm in the process of teaching myself C++ and am currently learning about dynamically allocating memory. Here's the code that I'm currently working with:

#include <iostream>

using namespace std;

int *memAdd(int* dyn_Point, int *lenPoint){
   int *new_Dyn_Point = new int[*lenPoint * 2];
   *lenPoint = *lenPoint * 2;
   for(int i = 0; i < *lenPoint; i++){
       new_Dyn_Point[i] = dyn_Point[i];
   }

   delete lenPoint;
   delete[] dyn_Point;
   return new_Dyn_Point;

}

int main(){

   int len = 2;
   int *lenPoint = &len;
   int current = 0;
   int val;
   int *dyn_Point = new int[len];


   cout << "Input a value for point 1: ";
   cin >> val;
   dyn_Point[current] = val;


   while(val > 0){
      current++;

      cout << "Input a value for point " << current+1 <<" (0 to exit): ";
      cin >> val;

      if(current+1 == len){
         *dyn_Point = *memAdd(dyn_Point, lenPoint);
         cout << len;
      }

      dyn_Point[current] = val;


   }

   for(int i = 0; i < len; i++){
     cout << &dyn_Point[i] << "\n";
     cout << dyn_Point[i] << "\n\n";

 }
 delete[] dyn_Point;

}

My Question: When adding more memory does it have to increment by a certain value?

Whenever I start with a value in my "len" variable that's not 2 my program will crash either as soon as I try and allocate more memory or after more memory has been allocated and even more has to be added a second time.

Is this how it's supposed to be or am I missing something entirely here?

Answer 1

Your while loop need a break

while() {

    //do your steps
    break;
}

In function memAdd following changes required :

// *lenPoint = *lenPoint * 2; 

// above line need to be commented else it will trouble the loop condition by causing over flow:

    for(int i = 0; i < (*lenPoint-1); i++){

// for loop is corrected to resolve the over flow

Below delete is unnecessary since you didn't allocate memory using this variable

// delete lenPoint;

For your question: When adding more memory does it have to increment by a certain value?

There is no hard and hard fast rule on this regard. std::vector<> double its size( memory allocation) whenever it is needed more memory. It is slightly different than your approach. You are doubling memory before reaching the allocated upper limit.

**Edit**

Compiled full code as OPs request

#include <iostream>

using namespace std;

int *memAdd(int* dyn_Point, int *lenPoint){
   int *new_Dyn_Point = new int[*lenPoint * 2];
  // *lenPoint = *lenPoint * 2;
   for(int i = 0; i < (*lenPoint-1); i++){
       new_Dyn_Point[i] = dyn_Point[i];
   }

   //delete lenPoint;
   delete[] dyn_Point;
   return new_Dyn_Point;

}

int main(){

   int len = 2;
   int *lenPoint = &len;
   int current = 0;
   int val;
   int *dyn_Point = new int[len];


   cout << "Input a value for point 1: ";
   cin >> val;
   dyn_Point[current] = val;


   while(val > 0){
      current++;

      cout << "Input a value for point " << current+1 <<" (0 to exit): ";
      cin >> val;

      if(current+1 == len){
         *dyn_Point = *memAdd(dyn_Point, lenPoint);
         cout << len<<"\n";
      }

      dyn_Point[current] = val;
     break;

   }

   for(int i = 0; i < len; i++){
     cout << dyn_Point[i] << "\n";
     cout << &dyn_Point[i] << "\n\n";

 }
 delete[] dyn_Point;

}

Answer 2

"My Question: When adding more memory does it have to increment by a certain value?"

Of course you have to manage your memory allocations using a design like this.

In particular you should obey the Rule of Three (Five) , and to copy all of the existing elements, when reallocating memory to increase to the necessary amount.

---

The much better choice than doing it all yourself (which is likely to be error prone), is to use a

std::vector<int> dyn_point;

and/or alike in your class.

Memory management is taken care of in the container implementations , and you don't need to bother about it.