swapping rows of dynamic 2d array in C

Question

I want to swap two rows of string array in C.

e.g:

first row , second row

after swap: second row, first row

How should this function looks like, swap_rows() func doesnt work. Should I use strcpy() function somehow?

What I did:


#define N 100


static char **str_tab;

void tab_alloc(const int M)
{
    str_tab = (char **)malloc((M  * sizeof(char *)));
    for (int i = 0; i < M; i++)
        str_tab[i] = (char *)malloc(N * sizeof(char));
}
void tab_fill()
{
    size_t M = _msize(str_tab) / sizeof(char *);
    for (int i = 0; i < M; i++)
        gets_s(str_tab[i], N);
}

void swap_rows() 
{
    int row1, row2;
    puts("Which rows u want swap?");
    puts("put 1:");
    scanf_s("%d", &row1);
    puts("put 2:");
    scanf_s("%d", &row2);
    char *temp = str_tab[row1];
    strcpy(str_tab[row1], str_tab[row2]);  //   str_tab[row1] = str_tab[row2];
    strcpy(str_tab[row2], temp); //   str_tab[row2] = temp;
}

[don't cast malloc](http://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc) — Barmar, May 05 '18 at 10:18
Just a hint, so your homework remains a challenge: How would you swap any two variables' values? — Ulrich Eckhardt, May 05 '18 at 10:19
I'm voting to close this question as off-topic because it looks like a write-my-code request. — alk, May 05 '18 at 10:40
char* tmp = str_tab[0]; str_tab[0] = str_tab[1]; str_tab[1] = tmp; — purec, May 05 '18 at 11:59

score 1 · Answer 1 · answered May 05 '18 at 10:18

1

You can simply swap the pointers.

void swap_rows(char **array, int row1, int row2) {
    char *temp = array[row1];
    array[row1] = array[row2];
    array[row2] = temp;
}

answered May 05 '18 at 10:18

Barmar

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swapping rows of dynamic 2d array in C

1 Answers1