Need to copy string array into a pointer string array

Question

I am writing a program that takes in a string array and sorts it then uses searching functions to search for a target. The string array I have set up works for all my sorting functions but I need the data to be in a pointer string array in order to make use of strcmp in my searching functions. I've attached the most recent attempt in my main function. The rest of the main function includes the sorting and searching function but what I am posting only contains the initialization of the arrays and printing them out. In the actual program, it will be copying the contents from the sorted array after whichever sorting function the user chooses completes. I just want to find out how I would copy the contents.

int main(void) {
    char arr[][MAX_LEN] = {"AAAAA", "a", "AAA", "aaaa", "AAa", "AAAAa", "AAa", "A", "aa", "Aaa"}; // initializes string array 
    char *target[] = {"A"};  //initializes target
    int n = sizeof(arr)/sizeof(arr[0]);  // initializes n 
    char *arry = (char* )malloc(n); // initizlizes *arry
    int i; 

    printf("Given string array is:");
    for (i = 0; i < n; i++)
        printf(" %s ", arr[i]); // prints out arr

    for (i = 0; i < n; i++) { // this was my first attempt to copy arr into *arr. 
        strcpy(arry[i], arr[i]);

        printf(" %s ", arry[i]); // used for testing to see if copying worked.
    }
}

Change to char *arr[] = {... but note that the strings will now be lieals and read-only. You can copy them, but cannot change the original. — Paul Ogilvie
– Paul Ogilvie, Commented Oct 16, 2019 at 13:57
Are you sure that you want a fixed size 2D array for this and not just an array of pointers to strings of variable length? — Lundin
– Lundin, Commented Oct 16, 2019 at 14:01
quote: "I need the data to be in a pointer string array in order to make use of strcmp in my searching functions" hmmm - what is wrong with strcmp(arr[0], "some string")? Or strcmp(arr[0], target[0]) ? I don't see why you would want to copy the array to "another array" in order to use strcmp. Seems an XY problem to me — 4386427
– 4386427, Commented Oct 16, 2019 at 14:05

Vlad from Moscow · Accepted Answer · 2019-10-16 14:00:19Z

1

In this declaration

char *arry = (char* )malloc(n);

there is allocated only a buffer for n characters.

What you want to do is

char ( *arry )[MAX_LEN] = (char* )malloc( sizeof( char[n][MAX_LEN] ) );

Another approach is the following.

char **arry = malloc( n * sizeof( char * ) );

for ( size_t i = 0; i < n; i++ )
{
    arry[i] = malloc( sizeof( char[MAX_LEN] ) ); 
}

In any case you will need to free all allocated memory.

In the first case you can just write

free( arry );

In the second case you have to write

for ( size_t i = 0; i < n; i++ )
{
    free( arry[i] );
}

free( arry );

edited Oct 16, 2019 at 14:00

answered Oct 16, 2019 at 13:57

Vlad from Moscow

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