Wordpress posts during the main loop - php

Question

While wordpress is doing the main loop, how does it determine which post belongs to the current page?
<?php while ( have_posts() ) : the_post(); ?>
<?php
get_template_part( 'template-parts/content', get_post_format() );
?>
<?php endwhile; ?>
In the above example, how does WordPress determine which post will be looped over?
Will the loop go through all the posts?

Answer 1

The main query runs for every page request. The main query makes use of the WP_Query class to fetch posts according to the parameters set via the URL structure of the page. WP_Query works exactly the same in the main query as it is with a custom query, the only diffirence here is the way how paramteres are passed. For the main query, the parameters passed is determined by URL, while for a custom query the parameters are manually set by the user
In short, this is what happens on every single page request made by the browser
The URL is checked and the current permalink structure is checked against the saved structure in the db. If any other permalink structure is in place in stead of the default permalink structure, the current permalink structure is checked against the default structure, and the URL is matched
A set of parameters with values are generated against the URL and permalink structure. Remember, the URL structure is a set of $_GET variables, this $_GET variables is a key/value pair that represents a parameter/value pair in WP_Query. The blank parameters that are still left (there are plenty) after the others have been filled from the URL are filled with default values. Here for instance is the posts per page which is set by get_option( 'posts_per_page' ) which represents the amount of posts set in the back end reading settings.
In short, so far, what the above says is, if you request a category page of your site, the URL is checked and is determined to be a category page. The category is identified and passed to the query as a key/value pair, which will at the end determine that the current page must show posts from this particular category
From all these parameters and their values, the SQL query is build accordingly which will query the database for posts according to the conditions set in the SQL query. The posts are returned and stored as objects
These post objects together with other important information is stored in one big object, the main query object, which is stored in the $wp_query global variable
Up till now, the loop has done absolutely nothing. All of the above happens whether or not you have a loop on the page or not. The loop only does two things
Access the main query object and loops through the post objects. How these objects are send to screen is determined by how the HTML markup, PHP and CSS is constructed inside the loop. The loop uses a while() loop which checks after the completion of one post if there is another post to display. If there is, the while() continues to execute, and it does so till no more posts are left and then kills execution. This is basic PHP, so be sure to check how a while() loop works
The second function the loop does is setting value of the $post global. This is done by the the_post() call inside the loop. On every iteration, the $post global is set to the current post being looped though
This is just a basic overview. Each process is huge and quite difficult to understand, and therefor, one can never address the whole complete process in detail. I hope this helps

Answer 2

I am pretty sure the short answer is, "it's in the query for the current page". The codex discusses the loop and understanding its use:
Using The Loop, WordPress processes each post to be displayed on the current page, and formats it according to how it matches specified criteria within The Loop tags. Any HTML or PHP code in the Loop will be processed on each post.
The Loop

Answer 3

Well I think show the post with this codes
<?php
get_template_part( 'loop', 'index' );
?>
u can use wp_query Object
<?php
// The Query
$args = array (
'post_type' => 'post',
'post_status' => 'publish',
);
$the_query = new WP_Query( $args );
// The Loop
if ( $the_query->have_posts() ) {
echo '<ul>';
while ( $the_query->have_posts() ) {
$the_query->the_post();
echo '<li>' . get_the_title() . '</li>';
}
echo '</ul>';
} else {
// no posts found
}
/* Restore original Post Data */
wp_reset_postdata();
?>
Other Code is here
<?php
if ( have_posts() ) {
while ( have_posts() ) {
the_title();
the_content();
}
}
?>