array returns

A quick demonstration/minimal reproduction of a Pawn bug related to returning arrays into the arguments of other functions.

Build and run this package to trigger the bug:

sampctl package run --forceBuild

Explanation

Consider the following two functions:

new string[12] = {"Hello world"};

stringOrigin() {
    return string;
}

returnString() {
    return stringOrigin();
}

Simple enough, right? There's a global string and a function that just returns that global. There is also a second function which returns the return value of the first function.

This code works, calling stringOrigin() which simply returns the string contents directly into a native. this is one "level" of function call depth.

new local[12];
strcat(local, stringOrigin(), sizeof(local));
print(local);

This code however, does not work. It calls a Pawn function which returns the value of the return value of stringOrigin(). this is two "levels" of function depth and causes the error.

new local[12];
strcat(local, returnString(), sizeof(local));
print(local);

Solution

Always use pass-by-reference to output array data from a function. The above functions would be rewritten as:

new string[12] = {"Hello world"};

stringOrigin(output[], len = sizeof output) {
    strcat(output, string, len);
    return 0; // return 0 generally means success
}

returnString(output[], len = sizeof output) {
    return stringOrigin(output, len); // it's okay to directly pass the return of stringOrigin here because stringOrigin only returns a single cell value (0) not an array.
}