从外部函数/类设置动态数组的新大小？

Question

My main code declares a pointer that needs to be resized from an external function. Ex:

double *vect =NULL;
classobj object;

object.func(vect);

//--- print the outcome
for(int j=0; j<4; ++j)
   cout << vect[j] << " .. " << endl;

where function func() is part of classobj defined in an another file (say classobj.h and .cpp ) as

void classobj::func(double *_vect){

  _vect  = new double[4];

  for(int j=0; j<4; ++j)
    _vect[j] = 3.0*j +1 ;

};

The problem is that vect has not been resized. I get segmentation fault. Any idea please on how to use pointers in this case?

Answer 1

You are passing a reference to your Array and then you are creating a new Array and assigning it to the pointer in the function. You Need to pass a pointer of the pointer and then reassign the address of that pointer:

void classobj::func(double **_vect){
    (*_vect)  = new double[4];

Although this solution will work I recommend using a std::vector for this purpose and passing it by reference to that function