Why does my array start with empty value?

Question

I can't wrap my head around this one.

When I create an array it begins with an empty value. The values that needs to be in the array starts as second.

Array:

Array ( 

 [0] => 

 [1] => Value 1 

 [2] => Value 2 

 [3] => Value 3

)

Code:

$categories = array();
$query2 = mysql_query("SELECT * FROM books_categories");
do{
    array_push($categories, $category['description']);
}while($category=mysql_fetch_assoc($query2));

How do I accomplish to get the first item in the array to be Value 1?

I think you should turn on error reporting and see what's up. — Alvin Wong, Dec 19 '12 at 12:26
@AlvinWong - there won't be any errors here; this is a logic problem, not a syntax or query problem. — SDC, Dec 19 '12 at 12:28
@MrSlippyFist - in case you're wondering why half the answers are telling you to stop using the `mysql_xx()` functions, it's because they're deprecated and not recommended for use. See [Why shouldn't I use mysql_* functions in PHP?](http://stackoverflow.com/questions/12859942/why-shouldnt-i-use-mysql-functions-in-php) for more info and what to do about it. — SDC, Dec 19 '12 at 12:29

score 21 · Accepted Answer · edited Dec 19 '12 at 18:03

21

It is because of do while loop try while loop

while($category=mysql_fetch_assoc($query2)){
    array_push($categories, $category['description']);
}

edited Dec 19 '12 at 18:03

NullPoiиteя

56,591
22
125
143

answered Dec 19 '12 at 12:24

senK

2,782
1
27
38

1

You're the fastest one and too fast. – Alvin Wong Dec 19 '12 at 12:24
1

Though it is recommended to do this: `while(($category = mysql_fetch_assoc($query2)) !== false)`. This will make sure it doesn't crash when there is an error in the query or if there are no rows. – Deep Frozen Dec 19 '12 at 12:27
@Rune your `!== false` bit isn't necessary; if it equals false, it will drop out of the loop just fine with the code in the answer because `$category` will be set to false, which will terminate the `while` loop. – SDC Dec 19 '12 at 12:32
@SDC That depends on your config. On my webhost, when there are no rows and I don't use the `!== false`, it errors. – Deep Frozen Dec 19 '12 at 12:34
@Rune - please elaborate. I stand by my previous comment that the while loop should drop out without it, but I'd be interested to know what config you have that would cause that behaviour, and what the error is that it generates. – SDC Dec 19 '12 at 12:43
@SDC Hmm, my host just updated last night and I don't get an error anymore if I try it.. Been a while since I've seen the error, since I always use `false`. It probably was a bug from my host that got solved, so ignore my comments. Even so, it will help to remove the annoying `assignment in condition` warnings in your editor (Zend Studio does that for example). – Deep Frozen Dec 19 '12 at 12:53

score 14 · Answer 2 · answered Dec 19 '12 at 12:25

The answer is very simple: you are pushing the first element before you read the first row. The right way of doing it would be with a pre-condition loop:

$categories = array();
$query2 = mysql_query("SELECT * FROM books_categories");

while($category=mysql_fetch_assoc($query2)) {
    array_push($categories, $category['description']);
}

And, please switch to using PDO.

score 12 · Answer 3 · edited Jun 20 '20 at 09:12

How do while loop works

The main difference from regular while loops is that the first iteration of a do-while loop is guaranteed to run (the truth expression is only checked at the end of the iteration), whereas it may not necessarily run with a regular while loop (the truth expression is checked at the beginning of each iteration, if it evaluates to FALSE right from the beginning, the loop execution would end immediately).source

so in your program what happened you are pushing the first element before you read the first row.

so use while instead

what wile loop will do ? as in flow chart it will check first than come inside loop body so element is push after read the first row

$categories = array();
$query2 = mysql_query("SELECT * FROM books_categories");

while($category=mysql_fetch_assoc($query2)) {
    array_push($categories, $category['description']);
}

Note

The entire ext/mysql PHP extension, which provides all functions named with the prefix mysql_, is officially deprecated as of PHP v5.5.0 and will be removed in the future. So use either PDO or MySQLi

Good read

The mysql extension is deprecated and will be removed in the future: use mysqli or PDO instead

Best answer. It's got a flowchart, a textual explanation, it mentions the deprecation of the API... what else do you need? — Zecc, Dec 19 '12 at 12:50

score 5 · Answer 4 · answered Dec 19 '12 at 12:24

Because you should use a while loop instead of the do-while loop.

while($category = mysql_fetch_assoc($query2)) {
    array_push($categories, $category['description']);
}

In your code instead in the first iteration of the loop (when entering the do block for the first time), $category is not set therefore setting the first array value to be empty.

score 5 · Answer 5 · answered Dec 19 '12 at 12:25

You first write the value (array_push()) into the array and then you actually grab the value (mysql_fetch_assoc()).

You need to first grab the value and then place it into your array!

$categories = array();
$query2 = mysql_query("SELECT * FROM books_categories");
while(($category = mysql_fetch_assoc($query2)) !=== false) {
    array_push($categories, $category['description']);
}

score 1 · Answer 6 · edited Dec 19 '12 at 12:44

1

Try doing this instead:

$categories = array();
$query2 = mysql_query('SELECT * FROM books_categories');
while($r = mysql_fetch_array($query2)){
    $categories[] = $r['description'];
}

edited Dec 19 '12 at 12:44

mauris

42,982
15
99
131

answered Dec 19 '12 at 12:25

Jonas m

2,646
3
22
43

@mauris - Someone here does not like spaces i see :-) – Jonas m Dec 19 '12 at 12:55
while I removed 3 spaces, I added 4 other spaces for indentation. Since -3 + 4 = 1, you can say that I still like spaces. – mauris Dec 19 '12 at 12:56
1

@maurius I approve your equation and accept your answer. You may now fly away :D – Jonas m Dec 19 '12 at 12:58

Why does my array start with empty value?

6 Answers6