First element of array (rest are fine) is a non-value half the time after shuffle

[np_123]

The problem I am having is that I'm getting weird output when I try to shuffle an array of 'strings'.
When the array contains {"hi", "hola", "amigo"} half the time I get the same back, the other half this {"8y@", "hola", "amigo"} where @ is a weird character looking like a skinny rectangle.

The method giving problems is the shufflestring method below. I've omitted for clarity two interface methods that don't modify anything:

C:

char **arr; shufflestring(arr, sz); /*sz is just length of the array*/ /* Modern Fisher-Yates shuffle */ void shufflestring(char *a[], int n) {         srand((unsigned)time(NULL));         for (int i = n - 1; i > 0; i--) {                 int j = rand() % (i + 1);                 char *temp;                 temp = a[i];                 a[i] = &a[j];                 a[j] = &temp;         } }

the exact same code works if instead of char** (array of 'strings' is what it's supposed to be) it's double a[] in the shuffle method and double* a being passed to it.
for example these work fine:

C:

/*Example1*/ char *str[5] = { "help", "hola", "hi", "amigo", "hitme"}; shufflestring(str, 5); /* Modern Fisher-Yates shuffle */ void shufflestring(char *a[], int n) {         srand((unsigned)time(NULL));         for (int i = n - 1; i > 0; i--) {                 int j = rand() % (i + 1);                 char *temp = a[i];                 a[i] = a[j];                 a[j] = temp;         } } /*Example2*/ double *arr; shufflereal(arr, sz); /* Modern Fisher-Yates shuffle */ void shufflereal(double a[], int n) {         srand((unsigned)time(NULL));         for (int i = n - 1; i > 0; i--) {                 int j = rand() % (i + 1);                 double temp = a[i];                 a[i] = a[j];                 a[j] = temp;         } }

[Insectoid]

I notice your char** example uses & in the swap, while your char*[] example does not. It's a long time since I've worked with C, but when you get random-looking strings, it's due to a pointer error. a[j] is already a pointer and doesn't need to be dereferenced. The reason your int example works is you are swapping the data directly, whereas your first looks like you're trying to swap pointers.

[np_123]

yes, thanks, I've gotten rid of the & now, but the same problem still occurs with one exception: instead of a garbage string the first element ends up empty. And I do agree it's a pointer error of sorts.

I can't figure out how to test the values in an dynamic array (im compiling, debugging using VS) but I'm starting to think that maybe the 'array of strings' that I wish to pass to the method isn't being created/stored properly. Reasoning: when I attempt to DebugOutputString(arr[0]) it crashes, but DebugOutputString(arr) works

The following methods are the relevant top-level method calls that initiate everything
Note: OOTaddr is an alias for char *, OOTint -> long, ADDR_SIZE == 1; (unfortunately the MyExecutorScan isn't code I wrote so while I 'mostly' understand what's happening, I can't really explain it)

C:

void MIO_sort_sortstring(OOTaddr *sp) {         char **arr;         OOTint sz;         MyExecutorScan(sp, "AI", &arr, &sz);         MIOSort_sortstring(arr, sz); } static void     MyExecutorScan (OOTaddr *sp, const char *param, ...) {    const char *pf = param;    va_list curr_arg;    va_start(curr_arg, param);    while (*pf)    {         switch(*pf)         {             case 'r':                 // Skip the function result stack position                 sp += ADDR_SIZE;                 break;             case 'A':                 {                     OOTaddr *arg_arrayp = va_arg(curr_arg, OOTaddr *);                     *arg_arrayp =  (OOTaddr) *sp;                     sp += ADDR_SIZE*2;                 }                 break;             case 'I':                 {                     OOTint *arg_intp = va_arg(curr_arg, OOTint *);                     *arg_intp = *((OOTint *) sp);                     sp += INT_SIZE;                 }                 break;         } // switch         pf++;     } // while     va_end(curr_arg); } // MyExecutorScan

[np_123]

I'm afraid it might have been a wild goose chase. The 'bug' seems to be not in my code, but in the program I'm extending (it's the OpenTuring project source, I doubt anyone's looked at that in years).

So what I gather the program is supposed to do is place/leave arguments on a stack frame which I later grab via pointer to the stack.

However, it appears to leave just the first element of the array on the stack at the and the rest I can't find.
How I came to that conclusion: DebugOutputString(*sp) prints hi ; and *(sp+2) is 3. (given the input i mentioned in the first post) Offsetting the pointer via *(sp + x) with values from -2 to 5 I can't find any other meaningful data

I don't honestly know if there's anything I can do to fix it without going into a bunch of obscure code. Unless there's some pointer offsetting magic I'm missing

[np_123]

and solved it - each further element of the array had an offset of 256.
as in, if 'hi' is at address x, hola is at x+256... meaning: *(sp) == "hi" and *(sp) + 256 == "hola"

I'm thinking the number 256 should be more than convenience, but doesn't ring any bells at the moment.

If anyone can confirm whether an offset of 256 (maybe it's a default string length/memory allocation?) can be assumed that'd be amazing