PHP while loop. Why does this work?

Question

I'm creating my first php site using tutorial for reference. I can't get my head around why the following works:

while ($row = mysql_fetch_array($result)){
  echo $row[1]. " ".row[2]."<br/>";
}

Specifically, how does the loop increment to the next row?

UPDATE: Thanks to all who bothered to provide an answer, including those who implored me to RTM. My problem was not understanding how while loops work, rather simply I couldn't see how the loop increments. THE ANSWER: From the PHP docs,

mysql_fetch_array: Returns an array that corresponds to the fetched row and moves the internal data pointer ahead

I see now, all is well.

BTW PLEASE USE "mysqli_fetch_array" specifically the mysqli. — les
– les, Commented Mar 3, 2014 at 2:49
Like c, the function mysql_fetch_array grabs a row from a table sequentially, like a placeholder and returns 0 or false when it reaches the end. this value gets assigned to row, but its also read by the if statement — jason dancks
– jason dancks, Commented Mar 3, 2014 at 2:50
Please accept the answer you're most satisfied with rather than putting the answer in the question itself. — Clay
– Clay, Commented May 5, 2017 at 19:27

Ja͢ck · Accepted Answer · 2014-03-03 02:48:26Z

2

You can rewrite that code to this equivalent:

$row = mysql_fetch_array($result); // fetch and advance
while ($row !== false) { // compare result against false
  echo $row[1]. " ".row[2]."<br/>";
  $row = mysql_fetch_array($result); // fetch and advance
}

An assignment yields a value which can then be used in a condition, though it's a good practice to put parentheses around the assignment:

// fetch and advance, compare fetched result against false
while (($row = mysql_fetch_array($result)) !== false) {
  echo $row[1]. " ".row[2]."<br/>";
}

answered Mar 3, 2014 at 2:48

Ja͢ck

174k39 gold badges269 silver badges317 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

ragol Over a year ago

There is an even better practice of not putting an assignment into a condition expression.

AKS Over a year ago

@ragol - I'm asking just for my own knowledge, why it is not a better practice to not put an assignment into the condition clause ? I've seen the pattern in many open source code (particularly in mail() calls). What's wrong with it ?

Ja͢ck Over a year ago

@ragol That's not exactly universal and really depends on which code convention you wish to follow.

slynagh Over a year ago

Thanks @Jack. Your answer hints at the cause of my confusion. I understand now that the mysql_fetch_array command advances the internal pointer so all is good.

ragol Over a year ago

@AyeshK: It is not bad to put assignments into conditional expressions. It's just that code becomes less readable, because it is not obvious at first glance whether it is a typo in a place where a comparison operator is expected or a real assignment. So you should think twice before putting an assignment into conditionals.

|

UserProg · Accepted Answer · 2014-03-03 02:52:43Z

1

mysql_fetch_array() will take a $result and save into $row in form an array. Using while loop, your program will loop the data in the array from the beginning until the end.

By the way, your codes should be like

while ($row = mysql_fetch_array($result)){
    echo $row['someData1']. " ".row['someData2']."<br/>";
}

If you want to iterate through the index, then the code looks like following but it will print the word Array as you will print the result in "that" specific index.

$indexCounter = 0;
while ($row = mysql_fetch_array($result)){
    echo $row[$indexCounter]."<br/>";
}

Hope this helps! Thank you.

answered Mar 3, 2014 at 2:52

UserProg

6391 gold badge9 silver badges23 bronze badges

Comments

esdebon · Accepted Answer · 2014-03-03 02:47:32Z

0

The mysql_fetch_array take the first element of $result then is $result have elements this work... is like take cards from a deck

answered Mar 3, 2014 at 2:47

esdebon

2,7815 gold badges27 silver badges34 bronze badges

Comments

Community · Accepted Answer · 2023-11-17 19:24:28Z

0

Take a read though the PHP While documentation. It might also be useful to learn what mysql_fetch_array() does and how it works. After you're done reading about that, don't use the mysql_* functions again because they're deprecated. Instead, use mysqli_* or PDO.

edited Nov 17, 2023 at 19:24

CommunityBot

11 silver badge

answered Mar 3, 2014 at 2:50

SeanWM

17.1k10 gold badges54 silver badges85 bronze badges

Collectives™ on Stack Overflow

PHP while loop. Why does this work?

4 Answers 4

6 Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

6 Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related