CODEWITHSUNDEEP
c++carrayssyntaxvariable-length-array
Vaibhav Punia
Vaibhav Punia

Reputation: 31

Passing 2D array to a funciton in c & c++

I tried same program for C & C++ i.e. passing 2D array to a function. The following program is working in C, but not working in C++, Please explain why so ?

IN C

#include<stdio.h> 
void pass(int n, int arr[][n])  // or void pass(int n, int (*arr)[n])
{
printf("%d",arr[0][0]);
//.....
}

int main()
{
int n;
scanf("%d",&n);  
int arr[n][n];
arr[0][0]=0;
pass(n,arr);
return 0;
}

IN C++

#include <bits/stdc++.h>
using namespace std;
void pass(int n, int arr[][n])  // or void pass(int n, int (*arr)[n])
{
cout << arr[0][0];
//.....
}

int main()
{
int n; 
   cin >> n;
int arr[n][n];
arr[0][0]=0;
pass(n,arr);
return 0;
}

3:29:error: use of parameter outside function body before ']' token void pass(int n, int arr[][n]) // or void pass(int n, int (*arr)[n])

6:9:error: 'arr' was not declared in this scope cout << arr[0][0];*

Upvotes: 2

Views: 129

Answers (1)

Vlad from Moscow
Vlad from Moscow

Reputation: 310980

These statements

int n;
scanf("%d",&n);  
int arr[n][n];

provide a declaration of a variable length array. A variable length array is an array dimensions of which depend on run-time values. It is a feature of C that compilers may conditionally support.

In C++ there is no such a standard feature. So the C++ compiler issues an error. In C++ dimensions of an array shall be compile-time constants. Though some C++ compilers can have their own C++ language extensions that can include the feature of variable length arrays.

In C++ use the class template std::vector instead of variable length arrays.

Upvotes: 2

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