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;