为指向指针数组的指针分配空间

Question

Good day. I have this: MAP_ITEM **map what I think is pointer to array of pointers (correct me if I am wrong please) and I have to allocate space for it. I can allocate space using malloc for 1 pointer, but have no idea how to do this. help would be really appreciated.

Answer 1

Here is an example , written for use with char **, but you can modify for your purposes:

char ** allocMemory(char ** a, int numStrings, int maxStrLen)
{
    int i;
    a = calloc(sizeof(char*)*(numStrings+1), sizeof(char*));
    for(i=0;i<numStrings; i++)
    {
      a[i] = calloc(sizeof(char)*maxStrLen + 1, sizeof(char));
    }
    return a;
}    

call it like this : (for array of 10 strings, each having maximum of 79 characters (leave one for NULL term)

char **arrayOfString;

arrayOfString = allocMemory(arrayOfString, 10, 80);

//

You also need to free memory created with allocMemory

void freeMemory(char ** a, int numStrings)
{
    int i;
    for(i=0;i<numStrings; i++)
        if(a[i]) free(a[i]);
    free(a);
}  

Call it like this :

freeMemory(arrayOfStrings, 10);

Answer 2

Import the stdlib.h Then use the malloc function. Where is an example for a one dimentional array:

int* my_in_array = (int*) malloc(sizeof(int) * size_of_my_array);

Note that malloc receives the number of bytes you want to allocate, so sizeof will tell you how many bytes a datatype will need (in this case an int, but it can be used for chars, structures, ...) and then I multiplicate it by size_of_my_array, wich is the number of elements of my array.

Now, just try to se this for you case.