Question

I am very familiar with Java and this is allowed there. However it looks like it’s not with C++. I’m getting an “invalid array assignment” when trying to assign valuesToGrab = updatingValues;.

//these are class attributes
int updatingValues[361] = {0};
int valuesToGrab[361] = {0};

//this is part of a function that is causing an error. 
for (unsigned int i=0; i < 10; i++) {

    //this fills values with 361 ints, and num_values gets set to 361. 
    sick_lms.GetSickScan(values,num_values);

    //values has 361 ints, but a size of 2882, so I copy all the ints to an array
    //of size 361 to "trim" the array.
    for(int z = 0; z < num_values; z++){
        updatingValues[z] = values[z];
    }

    //now I want to assign it to valuesToGrab (another program will be 
    //constantly grabbing this array, and it can't grab it while it's being
    //populated above or there will be issues
    valuesToGrab = updatingValues; // THROWING ERROR
}

I don’t want to have to iterate through updatingValues and add it to valuesToGrab one by one, but if I have to I will. Is there a way I can assign it in one function with C++?

Thanks,

Answer 1

The standard idiom for copying in C++ is

#include <algorithm>
...
std::copy(values, values+num_values, updatingValues);

make sure updatingValues is large enough or you will get overruns and bad things will happen.

That said in C++ we generally use a std::vector for this sort of task.

#include <vector>
...
std::vector<int> updatingValues=values; //calls vectors copy constructor

I vector does everything an array does (including static initalization in C++11), but has a well define interface. with iterators, size, empty, resize, push_back and more.

http://en.cppreference.com/w/cpp/algorithm/copy

http://en.cppreference.com/w/cpp/container/vector

EDIT
It is also worth noting that you can combine vector and arrays.

std::vector<int> vect(my_array, my_array+10);
//or
std::vector<int> another_vector;
...
another_vector.assign(my_array, my_array+10);//delayed population

and visa-versa

std::copy(vect.begin(), vect.end(), my_array); //copy vector into array.