在C中反转二维字符串集的功能不会比第一个和最后一个字符反转更多

Question

this is my first post in Stack Overflow. If I am missing anything, please let me know and I will try to add more information.

The function below is only supposed to use pointer operations and not array operations, as part of an assignment.

I have this function in C that is part of a larger program:

void reverseString(char strings[NUM_STRINGS][STRING_LENGTH])
{
    int i, j;
    char *ptr;                              //Declare pointer variable.
    for (i = 0; i < NUM_STRINGS; i++)
    {
        ptr = strings[i];
        do {                                //Here, we ignore the null terminators in the char array.
            ptr++;
        } while (*ptr != '\0');
        ptr--;                              //Iterate the pointer variable once downward.
        j = i;

        while (strings[j] < ptr)            //While loop for reversing the string
        {
            //printf("ptr: %d\n", ptr);
            //printf("strings[j]: %d\n", strings[j]);
            char temp = *strings[j];
            *strings[j++] = *ptr;
            *ptr-- = temp;
        }
    }
}

What it is supposed to do is accept a 2D char array with 4 strings and with each string holding up to 32 bytes of text. Then, it reverses each string in-place in the array. For example, if I input the four strings:

Hello World Good morning

It is supposed to then return:

olleH dlroW dooG gninrom

However, what ends up happening is that only the first and last characters of each string are reversed. For example:

oellH dorlW dooG gorninm

I have tried different solutions such as using i instead of j in the while loop or using prefix ++ instead of suffix, but nothing has worked yet. Any pointers as to what I should be looking for?

Thank you.

Answer 1

The solution is below. As described in my comment below, I added a secondary pointer instead of using strings[j] in the loop. The pointer now references to the beginning of the string instead of the entire array of strings.

void reverseString(char strings[NUM_STRINGS][STRING_LENGTH])
{
    int i, j;
    char *ptr;                              //Declare pointer variable.
    char *ptr2;
    for (i = 0; i < NUM_STRINGS; i++)
    {
        ptr = strings[i];
        ptr2 = strings[i];
        do {                                //Here, we ignore the null terminators in the char array.
            ptr++;
        } while (*ptr != '\0');
        ptr--;                              //Iterate the pointer variable once downward.
        j = i;

        while (ptr2 < ptr)          //While loop for reversing the string
        {
            char temp = *ptr2;
            *ptr2++ = *ptr;
            *ptr-- = temp;
        }
    }
}