What is the difference when a C++ function returns an array?

C functions have two behaviors when returning an array: a copy is returned by value, and changes to the copy do not affect the original array; a reference to the original array is returned by reference, and changes to the returned array are directly reflected in the original array.

#Differences when C functions return arrays

In C, functions can return various types of data, including arrays. When a function returns an array, there are two different behaviors:

• Return by value: Returns a copy of the array to the caller.
• Return by reference: Returns a reference to the array, not a copy.

Returning by value

When returning an array by value, the function creates a copy of the array and returns it to the caller. This creates a new copy of the memory, and any changes made to that copy will not affect the original array.

Syntax:

int* foo() {
    int arr[] = {1, 2, 3};
    return arr;
}

Practical case:

int main() {
    int* arr = foo();
    arr[0] = 10; // 更改副本值，不影响原始数组
    return 0;
}

Return by reference

Return an array by reference , the function directly returns a reference to the original array. This does not create a new copy of the memory, which means any changes made to the returned array will be reflected directly in the original array.

Grammar:

int* &bar() {
    static int arr[] = {1, 2, 3};
    return arr;
}

Practical case:

int main() {
    int* &arr = bar();
    arr[0] = 10; // 更改原始数组值
    return 0;
}

Difference

Features	Return by value	Return by reference
The returned copy	is	No
Changes to the returned array	Do not affect the original array	Reflected directly in the original array
Memory overhead	Create a copy, the memory overhead is high	Do not create a copy, the memory overhead is low
Efficiency	Low execution efficiency	High execution efficiency

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