returning array from function in c++

Question

this my program to return array from function in c++

#include <iostream>
using namespace std;

int *pTest(){
    static int a[] = {2,3,4,6,9};
    return a;
}

int main(){
    int *x;
    x = pTest();
    while(*x != NULL){
        cout << *x++ << "  ";
    }
}

according to me output should be 2 3 4 6 9
but on my machine output is 2 3 4 6 9 1,
why there is an extra 1 in the output.
i am using codeblocks ,gcc 4.8.1

Arrays don't have an implicit zero element. What would that mean if you had, say, struct S {S(int);}; and an array of S? — Qaz
– Qaz, Commented Oct 6, 2014 at 18:16
You should use container classes (e.g. std::vector for dynamically sized or std::array for fixed size) — crashmstr
– crashmstr, Commented Oct 6, 2014 at 18:18
You don't tell the loop when to stop. It is only string literals that put a NULL character in automatically. Try: static int a[] = {2,3,4,6,9,0}; — Galik
– Galik, Commented Oct 6, 2014 at 19:06

Mike Seymour · Accepted Answer · 2014-10-06 18:18:08Z

6

Arrays aren't zero-terminated, so the loop while (*x != NULL) will keep reading beyond the array until it finds a zero-valued word, or crashes, or causes some other undefined behaviour.

You'll either need to add a terminator to the array (if you can choose a value, perhaps zero, that won't be a valid array element), or return the length in some other way.

answered Oct 6, 2014 at 18:18

Mike Seymour

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Jimmy · Accepted Answer · 2014-10-06 18:42:15Z

0

You can use a count and take the size of the array. Like this:

int k = 0;
while(k <= sizeof(x)){
    cout  << "  "<< *x++;
    k++;

}

answered Oct 6, 2014 at 18:42

Jimmy

1

1 Comment

R Sahu Over a year ago

That is not correct. sizeof(x) will evaluate to sizeof(int*). Not what you are expecting to find.

Laura Maftei · Accepted Answer · 2014-10-06 18:42:55Z

0

With std::vector your function will be:

std::vector<int> ptest() {
    static const int a[] = {2,3,4,6,9};
    std::vector<int> vec (a, a + sizeof(a) / sizeof(a[0]) );
    return vec;
}

answered Oct 6, 2014 at 18:42

Laura Maftei

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