The `dword ptr` part is called a size directive. [This page][1] explains them, but it wasn&#39;t possible to direct-link to the correct section.

Basically, it means &quot;the size of the target operand is 32 bits&quot;, so this will bitwise-AND the 32-bit value at the address computed by taking the contents of the &lt;code&gt;ebp&lt;/code&gt; register and subtracting four with 0.


  [1]: http://www.cs.virginia.edu/~evans/cs216/guides/x86.html

Consider [the figure enclosed in this other question][1].
`ebp-4` is your first local variable and, seen as a dword pointer, it is the address of a 32 bit integer that has to be cleared.
Maybe your source starts with 

    Object x = null;


  [1]: https://stackoverflow.com/questions/1395591/what-is-exactly-the-base-pointer-and-stack-pointer-to-what-do-they-point

It is a 32bit declaration. If you type at the top of an assembly file the statement [bits 32], then you don&#39;t need to type DWORD PTR. So for example: 

    [bits 32]
    .
    .
    and  [ebp-4], 0

Are Apple touch icons bigger than 60x60 supported, and if so, what dimensions should I use for the iPad and iPhone?

What size should apple-touch-icon.png be for iPad and iPhone?

I heard that HTTP POST has no specification limit in data size it can be sent by. Is that true or is there just some really high limit?

Can HTTP POST be limitless?

Could someone explain what this means? (Intel Syntax, x86, Windows)

    and     dword ptr [ebp-4], 0

What does `dword ptr` mean?

Could someone explain what this means? (Intel Syntax, x86, Windows)
<pre><code class="hljs language-css">and dword ptr [ebp-4], 0
</code></pre>

I&#39;ve encoutered these to instructions IN &amp; OUT while reading &quot;Understanding Linux Kernel&quot; book. I&#39;ve looked up reference manual.

&gt; **5.1.9	I/O Instructions**
&gt; 
&gt; These instructions move data between
&gt; the processor’s I/O ports and a
&gt; register or memory.
&gt; 
&gt;     IN	Read from a port
&gt;     OUT	Write to a port
&gt;     INS/INSB	Input string from port/Input byte string from port 
&gt;     INS/INSW	Input string from port/Input word string from port 
&gt;     INS/INSD	Input string from port/Input doubleword string from port
&gt;     OUTS/OUTSB	Output string to port/Output byte string to port 
&gt;     OUTS/OUTSW	Output string to port/Output word string to port 
&gt;     OUTS/OUTSD	Output string to port/Output doubleword string to port

I didn&#39;t get few things:

1. &quot;processor’s I/O ports&quot;. What are they? Why would we want to read &amp; write &quot;strings&quot; to &amp; from these ports?
2. I never encoutered a scenerio where I need to use these instructions. When would I be needing these? 
3. Give some practical examples.

What are IN &amp; OUT instructions in x86 used for?

Alright so I have this line in my assembly

    MOV EAX, DWORD PTR DS:[ESI]

where ESI is `00402050` (ascii, &quot;123456789012&quot;)

After this instruction: `EAX = 34333231`


What really happened here? How is this value calculated, and why?  
Where could I get some good reference on this kind of thing?

What does MOV EAX, DWORD PTR DS:[ESI] mean and what does it do?

I&#39;m fairly new to Linux (Ubuntu 10.04) and a total novice to assembler. I was following some tutorials and I couldn&#39;t find anything specific to Linux.
So, my question is, what is a good package to compile/run assembler and what are the command line commands to compile/run for that package?


Compile/run assembler in Linux?

can anyone give me a comprehensive description about ORG directive?  
When and why is it used in assembly written applications?

Using Nasm on x86 or AMD64.

What does ORG Assembly Instruction do?

I&#39;m confused about machine code and native code in the context of .NET languages.

What is the difference between them? Are they the same?


What is the difference between native code, machine code and assembly code?

What is the difference between Trap and Interrupt?

If the terminology is different for different systems, then what do they mean on x86?

What is the difference between Trap and Interrupt?

I&#39;m not afraid to admit that I&#39;m somewhat of a C++ newbie, so this might seem like a silly question but....

I see DWORD used all over the place in code examples. When I look up what a DWORD truly means, its apparently just an unsigned int (0 to 4,294,967,295). So my question then is, why do we have DWORD? What does it give us that the integral type &#39;unsigned int&#39; does not? Does it have something to do with portability and machine differences?

Why in C++ do we use DWORD rather than unsigned int?

I know Python doesn&#39;t have pointers, but is there a way to have this yield `2` instead

    &gt;&gt;&gt; a = 1
    &gt;&gt;&gt; b = a # modify this line somehow so that b &quot;points to&quot; a
    &gt;&gt;&gt; a = 2
    &gt;&gt;&gt; b
    1

?

---

Here&#39;s an example: I want `form.data[&#39;field&#39;]` and `form.field.value` to always have the same value. It&#39;s not completely necessary, but I think it would be nice.

---

In PHP, for example, I can do this:

    &lt;?php
    
    class Form {
    	public $data = [];
    	public $fields;
    	
    	function __construct($fields) {
    		$this-&gt;fields = $fields;
    		foreach($this-&gt;fields as &amp;$field) {
    			$this-&gt;data[$field[&#39;id&#39;]] = &amp;$field[&#39;value&#39;];
    		}
    	}
    }
    
    $f = new Form([
    	[
    		&#39;id&#39; =&gt; &#39;fname&#39;,
    		&#39;value&#39; =&gt; &#39;George&#39;
    	],
    	[
    		&#39;id&#39; =&gt; &#39;lname&#39;,
    		&#39;value&#39; =&gt; &#39;Lucas&#39;
    	]
    ]);
    
    echo $f-&gt;data[&#39;fname&#39;], $f-&gt;fields[0][&#39;value&#39;]; # George George
    $f-&gt;data[&#39;fname&#39;] = &#39;Ralph&#39;;
    echo $f-&gt;data[&#39;fname&#39;], $f-&gt;fields[0][&#39;value&#39;]; # Ralph Ralph

Output:

    GeorgeGeorgeRalphRalph

[ideone](https://ideone.com/W1rZML)

----

Or like this in C++ (I think this is right, but my C++ is rusty):

    #include &lt;iostream&gt;
    using namespace std;
    
    int main() {
    	int* a;
    	int* b = a;
    	*a = 1;
    	cout &lt;&lt; *a &lt;&lt; endl &lt;&lt; *b &lt;&lt; endl; # 1 1
    	
    	return 0;
    }

Pointers in Python?

I have an array `int arr[5]` that is passed to a function `fillarr(int arr[])`:

    int fillarr(int arr[])
    {
        for(...);
        return arr;
    }

1. How can I return that array?
2. How will I use it, say I returned a pointer how am I going to access it?

Return array in a function

Whats the difference between a **Null pointer** &amp; a **Void pointer**?

What&#39;s the difference between a null pointer and a void pointer?

I have an `int` pointer (i.e., `int *count`) that I want to increment the integer being pointed at by using the `++` operator. I thought I would call:

    *count++;

However, I am getting a build warning *&quot;expression result unused&quot;*. I can: call

    *count += 1;

But, I would like to know how to use the `++` operator as well. Any ideas?

increment value of int being pointed to by pointer

Do I need to treat cases when I actully have nothing to move/copy with `memmove()`/`memcpy()` as edge cases

    int numberOfBytes = ...
    if( numberOfBytes != 0 ) {
        memmove( dest, source, numberOfBytes );
    }

or should I just call the function without checking

    int numberOfBytes = ...
    memmove( dest, source, numberOfBytes );

Is the check in the former snippet necessary?

Content Type	Original Author	Original Content on Stackoverflow
Question	小太郎	View Question on Stackoverflow
Solution 1 - Assembly	unwind	View Answer on Stackoverflow
Solution 2 - Assembly	mico	View Answer on Stackoverflow
Solution 3 - Assembly	L4m0r	View Answer on Stackoverflow

What does `dword ptr` mean?

Assembly Problem Overview

Assembly Solutions

Solution 1 - Assembly

Solution 2 - Assembly

Solution 3 - Assembly

Can HTTP POST be limitless?

What size should apple-touch-icon.png be for iPad and iPhone?

Attributions