CODEWITHSUNDEEP
c
Ananda
Ananda

Reputation: 1572

How to create an array of char pointer in C?

I have to create an array of char pointers each of them of size 10000000 using the best and optimized way to do this in C.

Upvotes: 0

Views: 1713

Answers (4)

ryucl0ud
ryucl0ud

Reputation: 622

I believe this is the optimal way because there is only one dynamic allocation, reducing overhead from fragmentation of the heap and the time taken to allocate. You can use the STRING_INDEX utility function to access the nth string.

Also, using calloc() instead of malloc() zeroes out buffer to ensure that all strings are NUL terminated.

#define STRING_SIZE 10000000
#define NUM_STRINGS 10

#define STRING_INDEX(array, string_idx) ((array) + (string_idx) * STRING_SIZE)

int main(int argc, char **argv) {
    char *array_of_strings = calloc(NUM_STRINGS, STRING_SIZE);

    // Access 8th character of 7th string
    char c = STRING_INDEX(array_of_strings, 7)[8];

    // Use array

    // Free array when done
    free(array_of_strings);

    return 0;
}

Upvotes: 2

Abhinav
Abhinav

Reputation: 2085

I think this will do (haven't checked for nulls though):

int i;
int num_arrays;
char **huge_char_array;
num_arrays = 10; //number of arrays you want.
huge_char_array = (char **)malloc(sizeof(char *) * num_arrays);
for(i = 0; i < num_arrays; i++)
{
    huge_char_array[i] = (char *)malloc(sizeof(char) * 10000000);
}

Upvotes: 4

Ed Swangren
Ed Swangren

Reputation: 124642

char *arr[SOME_SIZE];
for(int i = 0; i < SOME_SIZE; ++i) {
    arr[i] = malloc(10000000);
    if(!arr[i])
        // allocation failed, do something
}

Just realize that you're allocating ~9.5MB for every element in the array (i.e., SOME_SIZE * 10000000 total bytes)

Upvotes: 1

Mahmoud Fayez
Mahmoud Fayez

Reputation: 3459

I have been allocating 50K with each request I process this resulted in memory fragmentation. So I switched to allocate 50k * 100 = 5MB and reuse the pool when ever I need to allocate one more. If the requests increases beyond my pool capacity I double the pool size to avoid memory fragmentations. Based on this I would recommend allocating a huge chunk of memory maybe in your case 10 * 10000000 to reuse it. I am sorry but I cannot share the code that handle the pool here. Also use malloc and free and do not use new and delete.

malloc won't through exception it will simply return null if there are no memory available.

if you insist on using malloc for each element individually you can create a heap with maximum size to avoid fragmentations and in that case you will have to define the heap size.

please referee to MSDN for more details about how to create a heap and use it or the other allocation methods available for windows users. http://msdn.microsoft.com/en-us/library/windows/desktop/aa366533(v=vs.85).aspx

Upvotes: 1

Related Questions