I have a function and want to return a 2d array:
int flip[5][5](int input[5][5]);
But it returns an error: no function error allowed (this is a translation)
How can I fix this?
This works:
void flip(int input[5][5]);
-
stackoverflow.com/questions/3473438/return-array-in-a-functionvishal– vishal2015-11-27 16:05:13 +00:00Commented Nov 27, 2015 at 16:05
-
Please, post a mvce.skypjack– skypjack2015-11-27 16:05:40 +00:00Commented Nov 27, 2015 at 16:05
Add a comment
|
3 Answers
The syntax for returning an array is ugly. You're better off using a typedef, or auto.
auto flip(int input[5][5]) -> int[5][5];
However the problem you have is, you aren't passing the array to the function as a reference or pointer, which won't work.
typedef int myArray[5][5];
void foo(myArray& arr) {
//do stuff
}
int main() {
int arr[5][5];
foo(arr);
return 0;
}
As an aside, working with arrays like this is tedious, you're better off using a container from the STL.
2 Comments
black
I chose the method with typedef and it work. Thanks! Still one question: wanted to create a copy of the input argument arr in the function foo. How can I do this?
Ian
The only way to "copy" the array is to put it on the heap (via
new). If you create a local variable and try to return it from a function, it will get destroyed as soon as the function ends, that's no good. Keep in mind, if you use new you must use delete on it after, or you will have a memory leak.In this function declaration
void flip(int input[5][5]);
the parameter is implicitly adjusted to pointer to the first element of the array. So actually the function declaration looks like
void flip(int ( *input )[5] );
You may not return an array because arrays do not have a copy constructor.
You may return an array by reference provided that the array itself is not a local variable of the function.
So for example if your funciotn gets an array by reference then you may return this array from the function.
For example
int ( & flip(int ( &input )[5][5]) )[5][5];
You can wrap your array in a structure and return this structure along with the array.
For example
struct data
{
int a[5][5];
};
data flip( int input[5][5] );
answered Nov 27, 2015 at 16:11
Vlad from Moscow
313k27 gold badges204 silver badges358 bronze badges
1 Comment
Lingxi
A
typedef or using declaration will make the syntax human-readable.Use std::array<std::array<int, 5>, 5> instead of a built-in array type.
