How to return an array from a function by value in C++ [duplicate]

Question

I know it is inefficient to return an array by value instead of with a pointer. However, my CS class final has a requirement that a function is to return a 5 digit 1D array as a value. As such, I can not return the array by pointer. I am also unable to have any global variables.

I have tried

float FunctionName(){
float myVar[5];
//process data
return myVar;
}

I have also tried

float[] FunctionName(){
float myVar[5];
//process data
return myVar;
}

I even tried tricking the compiler with

float FunctionName(float myVar[5]) {
     //process data
     return myVar;
 }

I have read that it is impossible, but I am guessing it is just really weird or hard to do. I think it might be possible with an enum type, but I am unsure how I would set that up.

This question demonstrated more research than the dup, but the dup offers fairly comprehensive answers. — jxh
– jxh, Commented Dec 6, 2019 at 9:48
@jxh I actually found the duplicate, but the answers all said that it was impossible, and to just use pointers. I guess the 2 are similar enough though. — calebhk98
– calebhk98, Commented Dec 6, 2019 at 9:56
You sometimes have to read beyond the accepted answer to find the right answer. In this case, look at the second most popular answer in the dup. — jxh
– jxh, Commented Dec 6, 2019 at 9:57

Blaze · Accepted Answer · 2019-12-06 09:30:08Z

2

You can't return an array by value. However, you can do that with an std::array, which is a wrapper around an array:

#include <array>

std::array<float, 5> FunctionName() {
    std::array<float, 5> data;
    //process data
    return data;
}

answered Dec 6, 2019 at 9:30

Blaze

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2 Comments

calebhk98 Over a year ago

That actually works thanks. Is there any documentation for that specific array type? I haven't seen that before, but it already looks useful.

jxh Over a year ago

en.cppreference.com/w/cpp/container/array

Math Lover · Accepted Answer · 2019-12-06 09:35:48Z

0

You can return the pointer to array in C style doing:

float* FunctionName(){
float myVar[5];

float* p = (float*) malloc(sizeof(float) * 5);
//process data

return p;
}

answered Dec 6, 2019 at 9:35

Math Lover

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5 Comments

jxh Over a year ago

Better to use std::unique_ptr if you want to dynamically create the array.

Math Lover Over a year ago

Yes, I just supposed he wanted a fixed one of 5 elements as he said in the post

jxh Over a year ago

Perhaps, but your code uses malloc, which is dynamic. And the caller has to remember to use free, in a C++ program.

Math Lover Over a year ago

Right. I should improve my use of smart pointers ;)

jxh Over a year ago

tio.run/…

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