My personal understanding about wordpress's $ post global variables and the loop of the main loop.

 

During the past two days, when I was creating my own website blog, I encountered some problems with the $ post global variable when I was modifying the topic. Now make a point record.

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Http://codex.wordpress.org/Global_Variables

This is the official global variable list of wp. All wp global variables are involved, but most of them are not explained in detail.

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Some member attributes of $ post, refer to this URL: http://codex.wordpress.org/Function_Reference/get_post

The value returned by the get_post () function can be object/array.

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Online description of the loop and global variables in the main loop.

Http://fairyfish.net/2007/07/07/global-variables-and-the-wordpress-loop/

It is mentioned that:

InThe_post ()After a function is called, you can use many template functions and global variables.

And:

Global VariablesPostYou can use the following code to call it:

global $post;echo $post->post_title;

PassPostYou can also obtain the global variables: ID, post_author, post_date, post_excerpt, comment_count, and others.

According to the author, the $ post variable can only be called in the main loop, that is, it is not assigned a value before the_post () function is called.

However, reality is often contrary to human ideals. We often see some WP template Tutorials that use $ post-> XXX to get a lot of content, including title and content.

These calls are often placed outside the main loop. The most typical example is how to set the WordPress <meta> tag:

Http://www.chinaz.com/web/2011/0605/186189.shtml

$ Post-> post_content, $ post-> post_excerpt and so on are called, and the code is put in the header. in the PHP template file, we all know that the_post () and other functions are after the get_header () function.

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In this case, is there a conflict?

Here, a strong voice in my heart is calling to solve this conflict.

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I started to search for the source code of wp ......

First, I saw the code in the class-wp.php file:

Function register_globals (){
Global $ wp_query;
// Extract updated query vars back into global namespace.
Foreach (array) $ wp_query-> query_vars as $ key => $ value ){
$ GLOBALS [$ key] = $ value;
}

$ GLOBALS ['query _ string'] = $ this-> query_string;
$ GLOBALS ['posts'] = & $ wp_query-> posts;
$ GLOBALS ['post'] = (isset ($ wp_query-> post ))? $ Wp_query-> post: null;
$ GLOBALS ['request'] = $ wp_query-> request;

If (is_single () | is_page ()){
$ GLOBALS ['more'] = 1;
$ GLOBALS ['singles'] = 1;
}
}

Therefore, $ post and some similar global variables belong to the wp_query object.

In the query. php file, I found the definition of the wp_query object:

Function & query_posts ($ query ){
Unset ($ GLOBALS ['wp _ query']);
$ GLOBALS ['wp _ query'] = & new WP_Query ();
Return $ GLOBALS ['wp _ query']-> query ($ query );
}

Next, let's take a look at some class members and functions of WP_Query:

Class WP_Query {
//...
Var $ posts;
Var $ post;
//...
Function the_post (){
Global $ post;
$ This-> in_the_loop = true;

If ($ this-> current_post =-1) // loop has just started
Do_action_ref_array ('loop _ start', array (& $ this ));

$ Post = $ this-> next_post ();
Setup_postdata ($ post );
}
//...
Function next_post (){

$ This-> current_post ++;

$ This-> post = $ this-> posts [$ this-> current_post];
Return $ this-> post;
}
//...

} Function the_post (){
Global $ wp_query;

$ Wp_query-> the_post ();
}

Function have_posts (){
Global $ wp_query;

Return $ wp_query-> have_posts ();
}

Here we can clearly see the value assignment of $ post. Obviously, $ post belongs to one of the $ posts arrays.

The functions in the loop are also called $ wp_query member functions. Obviously, the_post () and $ post both come from the same object.

In this way, when this object is created, both of them already exist.

When I continued to search for the "Post =" string to confirm his assignment problem, I found that there were dozens of assignments in the entire WP, that is to say, $ post is often used for value assignment.

Although this does not completely prove that $ post has been assigned a value before the loop, it can at least prove that only the the_post () function in the loop can assign a value to $ post.

We have reason to believe that $ post has not been flushed out on the page, or when the program has not entered the main loop, it has been assigned a value.

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Due to the wide and profound wp program and my personal talents, I have never been able to fully explain this contradiction.

At this point, although the heart is unwilling, I had to give up temporarily.

 

 

As for how $ post is assigned a value as an object (because $ post-> ID proves that $ post is an object), I can only find some relevant clues, it cannot be interpreted at all times.

Slightly recorded here:

We know that $ post is actually one of the $ posts arrays, so I started with $ posts and found the get_posts () function in the query. php file, where I found some value assignment statements.

Including:

Function & get_posts (){
//...
$ This-> posts = $ wpdb-> get_col ($ this-> request );
//...
$ This-> posts = $ wpdb-> get_results ($ this-> request );
//...
$ This-> posts = apply_filters_ref_array ('the _ posts', array ($ this-> posts, & $ this ));
//...
If ($ this-> post_count> 0 ){
$ This-> post = $ this-> posts [0];
}
//...
}

 

What we can be certain is that $ posts's assignment must be traced back to the db class in the wp-db.php (nonsense, haha), and some strange functions. (Maybe, while solving this mystery, we can also solve the contradictions I mentioned above)

In addition, the function & get_post (& $ post, $ output = OBJECT, $ filter = 'Raw') in post. php may be used to describe the construction of this OBJECT (without looking into it ).

At this point, I have to lament once again the wide and profound nature of wp, as well as the contempt for my own "man-in-the-box man" behavior.

 

This log ends.

I don't know when these questions will be solved or whether they can be solved.

I hope that you will be grateful if you can help me solve this problem.