Piece of a functions stops working when put in a new function of its own

Question

I've got a .h file with:

JRAPI u64 list_directory_contents(char *directory);

In the .c file, I have a function that starts with:

u64 list_directory_contents (char *directory) {

And here is a piece of code:

// Convert directory name to wide-character string
u16  dir_address[268];  
u64 dest;               
int errorD = mbstowcs_s(&dest, dir_address, 268, directory, 268);

This works great, but I want to place this code in a new function.

In the .h file I make:

u16 get_absolute_path(char *directory);

And in the .c file I use:

u16 get_absolute_path(char *directory) {
    u16 return_address; 
    u64 dest;
    int errorDir = mbstowcs_s(&dest, return_address, 268, directory, 268);
    return return_address;
}

That is initiated at the old place with:

u16 dir_address = get_absolute_path(directory);

And now it doesn't work.

Clang says I need to put a & infront of the return_address:

int errorDir = mbstowcs_s(&dest, &return_address, 268, directory, 268); 

But then other problems start, and the value is not what it should be anymore and stops everything from working.

Placing this code in a function, what am I doing wrong?

u16 = Unsigned 16 bit integer, Unsigned short.
u64 = unsigned 64 bit integer, Unsigned long long.

When I declare the string as in the original code:

u16 return_address[268];    

I get the following message from clang:

warning: address of stack memory associated with 
      local variable 'return_address' returned [-Wreturn-stack-address]
    return return_address;
           ^~~~~~~~~~~~~~

---

Adding the [268] behind u16 return_address was the correct answer, but the error I get now is in a different part of the script that I have not addressed yet.

Answer 1

Take a look at the piece of code that works:

u16  dir_address[268];  
u64 dest;               
int errorD = mbstowcs_s(&dest, dir_address, 268, directory, 268);

Specifically at dir_address, then look at the code that doesn't work:

u16 return_address; 
u64 dest;
int errorDir = mbstowcs_s(&dest, return_address, 268, directory, 268);

Notice that you didn't declare return_address as an array like you did with dir_address. You could change this to:

u16 return_address[268]; 

But then 1) what you're returning doesn't match the return type, and 2) if it does match, you're returning a pointer to a local variable.

Your options here are to either allocate the memory dynamically:

u16 *get_absolute_path(char *directory) {
    u16 *return_address = malloc(268 * sizeof *return_address); 
    u64 dest;
    int errorDir = mbstowcs_s(&dest, return_address, 268, directory, 268);
    return return_address;
}

In which case the caller will need to free the memory, or have the caller pass in the buffer to fill:

void get_absolute_path(char *directory, u16 *return_address, int len) {
    u64 dest;
    int errorDir = mbstowcs_s(&dest, return_address, len, directory, len);
}