Previous: Flattening Arrays, Up: Array Manipulation   [Contents][Index]


16.4.11.4 How To Create and Populate Arrays

Besides working with arrays created by awk code, you can create arrays and populate them as you see fit, and then awk code can access them and manipulate them.

There are two important points about creating arrays from extension code:

The following C code is a simple test extension to create an array with two regular elements and with a subarray. The leading #include directives and boilerplate variable declarations (see Extension API Boilerplate) are omitted for brevity. The first step is to create a new array and then install it in the symbol table:

/* create_new_array --- create a named array */

static void
create_new_array()
{
    awk_array_t a_cookie;
    awk_array_t subarray;
    awk_value_t index, value;

    a_cookie = create_array();
    value.val_type = AWK_ARRAY;
    value.array_cookie = a_cookie;

    if (! sym_update("new_array", & value))
        printf("create_new_array: sym_update(\"new_array\") failed!\n");
    a_cookie = value.array_cookie;

Note how a_cookie is reset from the array_cookie field in the value structure.

The second step is to install two regular values into new_array:

    (void) make_const_string("hello", 5, & index);
    (void) make_const_string("world", 5, & value);
    if (! set_array_element(a_cookie, & index, & value)) {
        printf("fill_in_array: set_array_element failed\n");
        return;
    }

    (void) make_const_string("answer", 6, & index);
    (void) make_number(42.0, & value);
    if (! set_array_element(a_cookie, & index, & value)) {
        printf("fill_in_array: set_array_element failed\n");
        return;
    }

The third step is to create the subarray and install it:

    (void) make_const_string("subarray", 8, & index);
    subarray = create_array();
    value.val_type = AWK_ARRAY;
    value.array_cookie = subarray;
    if (! set_array_element(a_cookie, & index, & value)) {
        printf("fill_in_array: set_array_element failed\n");
        return;
    }
    subarray = value.array_cookie;

The final step is to populate the subarray with its own element:

    (void) make_const_string("foo", 3, & index);
    (void) make_const_string("bar", 3, & value);
    if (! set_array_element(subarray, & index, & value)) {
        printf("fill_in_array: set_array_element failed\n");
        return;
    }
}

Here is a sample script that loads the extension and then dumps the array:

@load "subarray"

function dumparray(name, array,     i)
{
    for (i in array)
        if (isarray(array[i]))
            dumparray(name "[\"" i "\"]", array[i])
        else
            printf("%s[\"%s\"] = %s\n", name, i, array[i])
}

BEGIN {
    dumparray("new_array", new_array);
}

Here is the result of running the script:

$ AWKLIBPATH=$PWD ./gawk -f subarray.awk
-| new_array["subarray"]["foo"] = bar
-| new_array["hello"] = world
-| new_array["answer"] = 42

(See Finding Extensions, for more information on the AWKLIBPATH environment variable.)


Previous: Flattening Arrays, Up: Array Manipulation   [Contents][Index]