Introduction
In PostgreSQL, the ListCell
struct is a key component for implementing linked lists, which we will use frequently on our contribution to Apache AGE. You can check its implementation in PostgreSQL's official GitHub Repository.
This blog post provides a concise overview of the ListCell
struct, its purpose, and significance, along with an example of iterating over a List
using ListCell
.
The ListCell Struct:
The ListCell
struct, defined in pg_list.h
, has two members:
-
next
: a pointer to the nextListCell
in the linked list, enabling traversal. -
data
: avoid
pointer to store the actual data in eachListCell
.
Iterating over a List using ListCell:
Let's consider an example of iterating over a list using ListCell
. Assume we have a List
of integers, and we want to print each element:
List *myList; // Assume we have a List containing integers
ListCell *cell;
foreach(cell, myList)
{
int *value = (int *) lfirst(cell);
printf("%d\n", *value);
}
In this example, we declare a ListCell
pointer cell
and use the foreach
macro provided by PostgreSQL to iterate over the myList
. Within the loop, we extract the integer value stored in each ListCell
using lfirst
, which returns a void
pointer. We then cast it to an int
pointer and dereference it to obtain the actual value, which we print.
The ListCell
struct is a vital component of PostgreSQL's linked list implementation. It facilitates the creation and manipulation of dynamic lists throughout the PostgreSQL source code, showcasing the system's flexibility and versatility. By utilizing ListCell
and its associated macros, such as foreach
, iterating over lists becomes straightforward and efficient.
Please note that this condensed blog post provides a high-level overview of the ListCell
struct and an example of iteration. For more detailed information, refer to the official PostgreSQL documentation and source code.
- Apache AGE. https://age.apache.org/.
- GitHub - apache/age - https://github.com/apache/age
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