question on pointer to new array structure

[bluefrog]

Hi
I'm attempting to create a pointer to a memory location for a structure. I am able to create such a pointer for an integer, but having problems with a structure.

The integer example is as follows:

#include <iostream>
int main () {

  int *tacos = new int[10];

  *tacos = 0;
  *(tacos+3) = 2;

  std::cout << "Value of tacos = " << tacos << std::endl;
  std::cout << "Value of *tacos = " << *tacos << std::endl;
  std::cout << "Value of *(tacos+3) = " << *(tacos+3) << std::endl;

  std::cout << "Value of tacos[0] = " << tacos[0] << std::endl;
  std::cout << "Value of tacos[3] = " << tacos[3] << std::endl;

  delete [] tacos;
  return 0;
}

No issues with the above. All works well. But the following causes a compile error for line 22 & 23.

#include <iostream>
#include <string>

int main() {

  struct choc {
    std::string choc_name;
    float weight;
    int calories;
  };

  choc *citems = new choc[10];


  *citems = {"Mocha Munch",0.3,200};
  *(citems+1) = {"Toffee caramel",0.3,300};

  // choc citem {"Mocha Munch",0.2,200};
  // std::cout << "Name : " << citem.choc_name << " weight " << citem.weight << " calories " << citem.calories << std::endl;

  std::cout << "Name : " << citems->choc_name << " weight " << citems->weight << " calories " << citems->calories << std::endl;
  // std::cout << "Name : " << citems[1]->choc_name << " weight " << citems[1]->weight << " calories " << citems[1]->calories << std::endl;
  std::cout << "Name : " << *(citems+1)->choc_name << " weight " << *(citems+1)->weight << " calories " << *(citems+1)->calories << std::endl;

  delete [] citems;
  return 0;
}

The compile error is:

choc_bar.cpp:23:29: error: no match for ‘operator*’ (operand type is ‘std::__cxx11::string {aka std::__cxx11::basic_string<char>}’)
   std::cout << "Name : " << *(citems+1)->choc_name << " weight " << *(citems+1)->weight << " calories " << *(citems+1)->calories << std::endl;

[Moschops]

This gives you a string: (citems+1)->weight

This is you attempting to call the dereference operator, *, on a string: *(citems+1)->weight

Try this instead:

std::cout << "Name : " << (citems+1)->choc_name << " weight " << (citems+1)->weight << " calories " << (citems+1)->calories << std::endl;

The -> operator dereferences the pointer (citems+1)


Basically, you're dereferencing the pointer to get the thing it's pointing at, and then you're trying to dereference that as well.

[bluefrog]

thanks, modified and it worked,

Why is it that for the new pointer to an integer in the first program I listed I have to use the notation *(taccos+3) to get to the value 2, but for the structure, in the second listing, I have to use (citems+1) ?

Output of the first program is:

Value of *tacos = 0
Value of *(tacos+3) = 2
Value of tacos[0] = 0
Value of tacos[3] = 2