Doubles (Floats)

Doubles are PHP's floats and are as easy to assign as longs, because their value is also contained directly in the union. The member in the zval.value container is dval; the corresponding type is IS_DOUBLE.
zval *new_double;

MAKE_STD_ZVAL(new_double);

new_double->type = IS_DOUBLE;
new_double->value.dval = 3.45;
Alternatively, you can use the macro ZVAL_DOUBLE:
zval *new_double;

MAKE_STD_ZVAL(new_double);
ZVAL_DOUBLE(new_double, 3.45);