cppreleasing.md

Some problems of releasing memory in C++ Back

• remember to create deconstructor of each class.

Class A {
private:
public:
    A() {}
    A(int b) {}
    
    /* remember to create this as follow */
    ~A() {}
}

• after using std::vector, clear() is just used to clear data, but the space of memory will still a problem for you. Therefore, remember to use swap() to release memory for each used vectors.

std::vector<T> v;

/* clear func just clears the data but not the space it takes */
v.clear();

/* by calling this func, space will be really released */
std::vector<T>(v).swap(v);

• when using new to create instances, please remember to release memory by using delete

A a = new A();

/* release */
delete a;

• some attention points about char*

  • normal situation:

  /* allocate 30 bytes to house a string */
  char* str = new char [30];
  
  /* release */
  delete [] str;

  • remember to release when relocate a pointer to another one:

  char* str = new char [30];
  
  str = new char [60];
  
  /* this will only release the next 60 bytes, but not the 30 bytes before */
  delete [] str;

  • notice about pointers assignments:

  char* str1 = new char [30];
  char* str2 = new char [40];
  
  strcpy(str1, "memory leak");
  
  /* try not to do this, or you'll never free those 40 bytes of character */
  str2 = str1
  
  delete [] str2;
  /* a disater is comming, and access violation */
  delete [] str1;

  • block region will never collect memory after exiting the program:

  void Leak(int x) {
      char* p = new cha [x];
      
      /* if you don't do show, oops, memory leak happens */
      delete [] p;
  }

  • delete by itself is just to delete a single object, and delete [] can free the whole array:

  char* one = new char;
  /* something wrong */
  delete [] one;
  
  char* many = new char [40];
  /* something wrong */
  delete many;