A few questions

[Channel5]

Recently I got some suggestions on my code, which aroused a few questions:

1) I noticed that in the if statement there where no {}

For example, instead of:

if($var == 1){
echo $var;
}

it was...

if($var == 1)
echo $var;

Are the {} no longer necessary?

If so, does not using them only work in later versions of php?

2) What's the different between !$var and empty($var)?

If a variable's empty, I've been using !$var up to this point and wasn't aware of empty($var).

Would I be better of using empty()?

If so, what's the reason?

3) I've noticed some coders use === or !== instead of == or != in there if statements...

What's the difference?

Does one have a benefit over the other?

As always feedback much appreciated. Since I started learning php, this site has been an amazing help.

[bradgrafelman]

Channel5 wrote:

Are the {} no longer necessary?

It depends. If the code inside the {}'s is a single command (e.g. a single echo() statement or something of that nature), then no, the {}'s aren't necessary. Some coders prefer to always use the {} so as to avoid confusion and/or forgetting to add them in case you expand the if() block to include more than one statement.

Personally, I will use the condensed form you see above. Sometimes I'll even condense things a bit further using the ternary syntax; this:

if($var == 1) {
    echo "one";
} else {
    echo "not one";
}

would become:

echo ($var == 1 ? "one" : "not one");

Channel5 wrote:

2) What's the different between !$var and empty($var)?

If a variable's empty, I've been using !$var up to this point and wasn't aware of empty($var).

Would I be better of using empty()?

If so, what's the reason?

The main difference is that [man]empty/man would be preferred if you don't know whether or not the variable exists. For example, this code:

if(!$_GET['id']) {

generates an E_NOTICE level error message, whereas this code does not:

if(empty($_GET['id'])) {

EDIT: Forgot to answer the last question:

Channel5 wrote:

3) I've noticed some coders use === or !== instead of == or != in there if statements...

What's the difference?

Does one have a benefit over the other?

Those two operators compare the value and type of the two operands. More information about the two can be found here: [man]operators.comparison[/man]. Here's a brief example:

var_dump("0" === 0); // bool(false)
var_dump(NULL === FALSE); // bool(false)

Note that if you replaced the === operator with the == operator, both of the above statements would have been true.

EDIT2: Thought of a better example; check out the manual for [man]strpos/man. Obviously, FALSE and 0 are two very different return values, but since you'd most likely want to differentiate between the two, a simple '==' comparison won't cut it and you must instead use '===' to specifically test for boolean FALSE rather than the integer 0.

[Channel5]

Thanks for the feedback, Brad.

I'd seen the ternary syntax in others code before but never understood it -- boy is this is going to come in handy. 🙂

I have a few more questions from your answers:

1) Concerning !$var vs. empty($var), what's an E_NOTICE level error message?

Could you give an example of when a good time to use each would be?

Right now, I'm thinking about forms. If any of the varibles are left empty, it would return an error message.

Example:

if(!$name || !$email){
  echo "Error.";
}

Would it be better to use empty() over ! in this case?

2) Are you saying that === is only used for booleans?

For example, as opposed to comparing variables:

if($pass == $confirmpass){
  echo 'Good.';
}

3) Also, how about single quotes vs. double quotes?

Somehow, even though I know I've read explanations in the past, I've never gotten clear on the difference -- or when it's preferrable to use one over the other.

[bradgrafelman]

Channel5;10916776 wrote:

1) Concerning !$var vs. empty($var), what's an E_NOTICE level error message?

Well, an E_NOTICE error message is just referencing what level of error it is; E_NOTICE is one of the predefined PHP constants. You can see the following manual page for more information about them: [man]errorfunc.constants[/man].

I had assumed you were using $POST and/or $GET to retrieve incoming data, in which case referencing something like $POST['name'] when $POST['name'] doesn't actually exist (e.g. no form was submitted yet) would cause an E_NOTICE-level error message stating that the specified array index doesn't exist.

Channel5;10916776 wrote:

Right now, I'm thinking about forms. If any of the varibles are left empty, it would return an error message.

Example:

if(!$name || !$email){
  echo "Error.";
}

Would it be better to use empty() over ! in this case?

It would be better to use it, yes, but even before that if() statement; where do you define the $name and $email variables in such a situation?

Channel5;10916776 wrote:

2) Are you saying that === is only used for booleans?

No, but it returns a boolean answer - true or false, just like the '==' operator does.

Channel5;10916776 wrote:

3) Also, how about single quotes vs. double quotes?

Somehow, even though I know I've read explanations in the past, I've never gotten clear on the difference -- or when it's preferrable to use one over the other.

It's a matter of personal preference, really; I don't know that empirical evidence showed that using one was any faster than the other (or that the difference was statistically significant in any situation).

Note that the only difference, as pointed out on the manual page for a [man]string[/man], is that variable interpolation and the special escape sequences (e.g. "\n" for a new line) don't happen in a single-quoted string. Example:

<?php
$foo = "bar";

echo '$foo\n'; // outputs a literal dollar sign, "foo", a backslash, and the letter "n"
echo "$foo\n"; // outputs "bar" followed by a line break

[onicsoft]

The === and !== compares the var on the data type level. If they are different data type, int vs str then it will return false. The == and != just compares the var's themself, so a str "0" is true when compared to a int 0. If using the === or !== then it would return false.

More reading fun: Here and here

---

Single quote does not phrase var's and double quotes does phrase vars inside the quotes.

$emotion = 'happy';
echo 'the big yellow guy is $emotion';
//outputs - the big yellow guy is $emotion

echo "the big yellow guy is $emotion";
//outputs - the big yellow guy is happy

/*Now using periods with it might get a bit confusing.
The two below does the exact same thing, but the one
with the double quotes uses more memory.
*/

echo 'the big yellow guy is '.$emotion;
//outputs - the big yellow guy is happy

echo "the big yellow guy is ".$emotion;
//outputs - the big yellow guy is happy

Another thing if you have to echo a string and don't want to escape a certain quote then you can use the other one.

echo '<a href="'.$var.'">link</a>';
echo "<a href='$var'>link</a>";

Does the same, but double quotes phrases the var without having to use a period to append the extra strings/var on to it and might be easier to read. Even though it uses more memory when doing it. Using the single quote you don't have to escape a " and it a little more bit difficult to read.

To use single quotes vs double. It is a matter of what you like to do. Just put the var in the string to be phrase and use more memory. If you want to / escape quotes. If you want to use dots to include the vars outside the quote strings.

Extra reading over this: Here

I hope I wasn't to confusing. I had the same questions as you at one time, but found ton of results with google to answer my questions over it. Plus, it doesn't hurt to ask though.

bradgrafelman: I also like using - echo ($var == 1 ? "one" : "not one"); I find it is simple and effect when you need to do just one line commands for the if else statements.
.

[Channel5]

Thanks guys. I'm pretty clear on the === vs == and " vs ' issues now.

However, I'm still a little hazy on when to use empty() vs ! though.

Basically, my two uses are in cases like these:

$var = $_POST[var]; // From a form

if(!$var){
  echo 'Code';
}

And:

$result = mysql_query("SELECT * FROM database")
or die(mysql_error());
$row = mysql_fetch_array($result);

if(!$row[var])"
  echo 'Code';
}

And in similar cases, how about the opposite?

Is this:

if(!empty($row[var])){
  echo 'Code';
}

Better than this:

if($row[var]){
  echo 'Code';
}

Just wondering if I should go back and change these all to empty().

Also, what's the difference between, for example, $POST['var'] and $POST[var]?

I started coding with things like $GET['var'] and recently dropped the 's to $GET[var].

[bradgrafelman]

The problem with code like this:

$var = $_POST[var]; // From a form 

is that if the specified index of the $_POST array doesn't exist, you're running into the E_NOTICE error I mentioned above. That's why I write such code like so:

$var = (isset($_POST['var']) ? $_POST['var'] : '');

Otherwise, you might do something like:

if(!empty($_POST['submit'])) {
    // know that $_POST['submit'] exists, process form data
}

Again, using [man]empty/man avoids the E_NOTICE error because it is a function specifically designed for this situation.

Channel5 wrote:

Also, what's the difference between, for example, $POST['var'] and $POST[var]?

Simple; the latter of the two isn't entirely correct. :p Array indexes in arrays like:

$_POST = array('var' => 'value');

are strings. In PHP, all strings are denoted by some form of an identifier, be it single quotes, double quotes, or a heredoc/nowdoc syntax.

The absence of quotations in $_POST[var] as you have it would suggest that var is a constant (see: [man]constants[/man] if you don't know what these are). In the case where no such constant is defined, PHP will throw an E_NOTICE error - "Use of undefined constant ..." and assume that you meant the index to be a string.

Depending upon the name, however, you can either cause parse errors or experience odd behavior. Some examples:

echo $_POST[var]; // parse error; 'var' has special meaning when not in a string

define('foo', 'FOO BAR');
$_POST['foo'] = 'Hello world!';

echo $_POST[foo]; // PHP error: Notice: Undefined index: FOO BAR

EDIT: Note that variable interpolation in a [man]string[/man] has different rules. The following two lines are correct ways to reference an array index inside a string:

echo "Hello $_POST[foo]!";
echo "Hello {$_POST['foo']}!";