=proto
int duk_push_c_function(duk_context *ctx, duk_c_function func, int nargs);

=stack
[ ... ] -> [ ... func! ]

=summary
<p>Push a new function object, associated with a C function, to the stack.
The function object is an Ecmascript function object; when called, <code>func</code>
will be called using the Duktape/C function interface.  Returns non-negative index
(relative to stack bottom) of the pushed function.</p>

<p>The <code>nargs</code> argument controls how the value stack looks like when
<code>func</code> is entered:</p>

<ul>
<li>If <code>nargs</code> is >= 0, it indicates the exact number of arguments the
    function expects to see; extra arguments are discarded and missing arguments
    are filled in with <code>undefined</code> values.  Upon entry to the function, value
    stack top will always match <code>nargs</code>.</li>
<li>If <code>nargs</code> is set to <code>DUK_VARARGS</code>, the value stack will contain
    actual (variable) call arguments and the function needs to check actual argument
    count with <code><a href="#duk_get_top">duk_get_top()</a></code>.</li>
</ul>

=example
int my_addtwo(duk_context *ctx) {
    double a, b;

    /* Here one can expect that duk_get_top(ctx) == 2, because nargs
     * for duk_push_c_function() is 2.
     */

    a = duk_get_number(ctx, 0);
    b = duk_get_number(ctx, 1);
    duk_push_number(ctx, a + b);
    return 1;   /*  1 = return value at top
                 *  0 = return 'undefined'
                 * <0 = throw error (use DUK_RET_xxx constants)
                 */
}

int test(void) {
    int func_idx;

    func_idx = duk_push_c_function(ctx, my_addtwo, 2);
    duk_push_int(ctx, 2);
    duk_push_int(ctx, 3);  /* -> [ ... func 2 3 ] */
    duk_call(ctx, 2);      /* -> [ ... res ] */
    printf("2+3 is %d\n", duk_get_int(ctx, -1));
    duk_pop(ctx);
}

=tags
stack
function