reversing a string array within a 2D array using pointer in c

Question

i need to write a function that takes a 2D string array, takes each string and in the array and reverses it.

so if if have:

{"first", "second", "third", "fourth"}

it would change it to:

{"tsrif", "dnoces", "driht", "htruof"}

but it needs to do it without returning a different copy, in other words i have to use pointer to rearrange it.

the method signature would look like this:

void reverseStrings(char strings[NUM_STRINGS][STRING_LENGTH]){
    char *ptr = &strings[0][0];
}

so far i have this:

char* reverseOneString(char s[STRING_LENGTH]){
char temp;
char *p = &s[0];

while(*p != '\0'){
    p++;
}
return p;
}

void reverseStrings(char strings[NUM_STRINGS][STRING_LENGTH]){
printf("reversing strings\n");
char *ptr = &strings[0][0];

for(int i= 0; i < NUM_STRINGS; i++){
    char *nptr = reverseOneString(strings[i]) - 1;
    while(nptr >= ptr){
    
        char temp = *ptr;
        *ptr = *nptr;
        *nptr = temp;
        
        nptr--;
        ptr++;
        while(*ptr == "\0"){
        ptr++;
        }
    }
    printf("\n");
}
}

but it isn't really working

And what is your question? What have you tried and what specific problem do you have? — kaylum, Jun 01 '21 at 07:09
Tip: Use `char** strings` instead of the often misleading array variant which means something quite different. — tadman, Jun 01 '21 at 07:10
Tip: You can't change an inline string. You need to copy it to a mutable buffer first, or you can live with undefined behaviour. — tadman, Jun 01 '21 at 07:11
@tadman, `char** strings` parameter will not be correct if the variable passed as `string` is declared as 2D array — tstanisl, Jun 01 '21 at 07:33
@tstanisl I'm referencing the "if have" comment with `{ "first", ... }` which admittedly is lacking type definition. — tadman, Jun 01 '21 at 07:42
Does this answer your question? [Reversing a string in C](https://stackoverflow.com/questions/784417/reversing-a-string-in-c) — Cortex0101, Jun 01 '21 at 10:24
`{"first", "second", "third", "fourth"}` is a 1-dimensional array of strings. — William Pursell, Jun 01 '21 at 22:21

score 0 · Accepted Answer · answered Jun 01 '21 at 21:45

This is what i was looking for, sorry if I didn't explain well

char* reverseOneString(char s[STRING_LENGTH]){
    char temp;
    char *p = &s[0];
 
    while(*p != '\0'){
        p++;
    }
    p--;
    printf("one reverse is sending back %c\n", *p);
    return p;
}

void reverseStrings(char strings[NUM_STRINGS][STRING_LENGTH])
{
    char *ptr = &strings[0][0];
    printf("reversing strings\n");
    printf("First pointer is pointing to: %c\n", *ptr);

    for (int i = 0; i < NUM_STRINGS; i++) {
        int counter = 0;
        char* nptr = reverseOneString(strings[i]);
        while (nptr > ptr) {
            printf("ptr: %c  nptr: %c\n", *ptr, *nptr);

            char temp = *ptr;
            *ptr = *nptr;
            *nptr = temp;

            nptr--;
            counter++;
            ptr++;
            while(*ptr == '\0'){
                ++ptr;
            }        
        }
    
        ptr += STRING_LENGTH - counter;
        printf("this is the process value of ptr %c\n", *ptr);
        printf("\n");
    }

}

Are you saying this the answer to your question then? – ryyker Jun 01 '21 at 21:50 — ryyker, Jun 01 '21 at 21:50
...then you should mark it as accepted :) – ryyker Jun 04 '21 at 16:36 — ryyker, Jun 04 '21 at 16:36
thanks lol. Im still a noob on stack overflow – Hackerman Jun 06 '21 at 13:45 — Hackerman, Jun 06 '21 at 13:45

reversing a string array within a 2D array using pointer in c

1 Answers1