How to pass Dynamic Array by reference C++

Question

I'm having trouble understanding how to pass a dynamic array by reference in C++.

I've recreated the problem in this small isolated code sample:

#include <iostream> using namespace std; void defineArray(int*); int main() { int * myArray; defineArray(myArray); /** CAUSES SEG FAULT*/ //cout<<(*(myArray)); //desired output is 0 return 0; } void defineArray(int*myArray) { int sizeOfArray; cout<<"How big do you want your array:"; cin>>sizeOfArray; /** Dynamically allocate array with user-specified size*/ myArray=new int [sizeOfArray]; /** Define Values for our array*/ for(int i = 0; i < sizeOfArray; i++) { (*(myArray+i))=i; cout<<(*(myArray+i)); } }

Is there a particular reason why you don't use myArray[i] = i Code looks much cleaner that way — Rohith R
– Rohith R, Commented Oct 8, 2016 at 5:34

songyuanyao · Accepted Answer · 2016-10-08 05:34:46Z

myArray is passed by value itself, any modification on myArray (such as myArray=new int [sizeOfArray];) has nothing to do with the original variable, myArray in main() is still dangled.

To make it passed by reference, change

void defineArray(int*myArray)

to

void defineArray(int*& myArray)

Christian Hackl · Accepted Answer · 2016-10-08 11:48:53Z

This solution is hopelessly complicated. You don't need new[], pointers or even a reference parameter. In C++, the concept of "dynamic arrays" is best represented by std::vector, which you can just just use as a return value:

#include <iostream> #include <vector> std::vector<int> defineArray(); int main() { auto myArray = defineArray(); if (!myArray.empty()) { std::cout << myArray[0] << "\n";; } } std::vector<int> defineArray() { int sizeOfArray; std::cout << "How big do you want your array:"; std::cin >> sizeOfArray; std::vector<int> myArray; for (int i = 0; i < sizeOfArray; i++) { myArray.push_back(i); std::cout<< myArray[i] << "\n"; } return myArray; }

push_back will work intelligently enough and not allocate new memory all the time. If this still concerns you, then you can call reserve before adding the elements.

Collectives™ on Stack Overflow

How to pass Dynamic Array by reference C++

2 Answers 2

Comments

Comments

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Related