soughting thru null data retreived from table

synfield

I have a table which stores up to 4 image path's i.e picture1, 2..etc. IF picture1 has a directory path and picture2 has a NULL value, but picture3 also has a directory path, my code will only delete the picture1 image file as the second while loop fails when it encounters the NULL value. However I thought the outside while loop would continue through each element of the 'results' array returned from the query.

How can I get this to search all of the array elements returned from the query.

I'm not worried about the objective (there are better ways to acheive this) only the problem concerning adhoc NULL values that are indiscriminantly placed between my valid data, then filtering these values via a loop.

============================================

$del_files_sql = "select picture1, picture2, picture3, picture4
								from story 
								where id = $story";

		$result = mysql_query($del_files_sql);
		if($result){
			while ($pic = mysql_fetch_array($result)) {
			/*while ($pic = mysql_fetch_assoc($result)) { // nb this does what the mysql_fetch_array($result)) does only faster X2!
				while (list($key,$val) = each($pic)) { 
				$$key = $val; 
				}*/
				$z = 1; 
				while ($pic[picture.$z]){
					$del_file = unlink($pic[picture.$z]);
						if ($del_file){
						$status .= "<p>Deleted file ".$pic[picture.$z]." successfully</p>\n";
						}else{
						$status .= "<p>Can't delete file ".$pic[picture.$z].", please try again later</p>\n";
						}
				$z++;
				}#end while
			}
			$del_dir = rmdir($the_path."/".$story);
				if ($del_dir){
					$status .= "<p>Deleted directory ".$the_path."/".$story." successfully</p>\n";
					}else{
					$status .= "<p>Can't delete directory ".$the_path."/".$story.", please try again later</p>\n";
					}

=============================================

Cheers

Synfield 😕

Weedpacket

Well, it looks like a case for database normalisation; then you can filter NULLs out at the query...

But if you want to skip nulls: rewrite the loops so that they don't depend on the contents of the arrays but only on the number of elements. (i.e., use for loops instead of whiles).

Then, if you want to skip a field $pic["picture".$z],

if(is_null($pic["picture".$z]))
    continue;

synfield

Weedpacket, thanks for your reply, will look at your options - btw is it correct to say that the error is with mysql_fetch_array() functon, because if the value of the field is null the key is also not returned, which causes problems in condtion test statements.

Cheers

Synfield

Weedpacket

I was just thinking a little while ago about how there seems to be some haziness within PHP about whether a given variable is set/unset, empty/nonempty, or null/nonnull - apparently arising out of its loosely-typed nature. Eg.:

$foo = 'bar';
echo "\$foo is" .  (!isset($foo)?' not':'') . " set\n";
$foo = null;
echo "\$foo is" .  (!isset($foo)?' not':'') . " set\n";

tells me that setting a variable to null is equivalent to unsetting it.

Variable references appear to aggravate this, and PHP bug reports have been generated due to inconsistencies in behaviour (e.g., setting a variable to null is not always equivalent to unsetting it! Not when the variable is a $_SESSION[] element!).

Confusion over mysql_fetch_array's returning of nulls may be symptomatic of this.

Or maybe it's just me, and no-one's been able to explain it to me clearly enough 🙂

synfield

Yeah, I get tripped up on whether to use isset($foo) or empty($foo) particularly when sending query vars from one page to another. My understanding is that the form will create the vars regardless whether they have values or not, therefore isset will always be true, and if these values are 0 then empty is also true.

Anyway, thanks to Weedpacket the following script seems to work. I've posted it to demonstarte a point, the objective of this code can be done more simply by reading the directory that the files are in and deleting them before removing the directory they're in. This code refers to multiple file uploads from a form and the clean yp of the db and file directory if there are any errors uncounted on the way.

==============================================

if ($error||$mime_error)
	{
			$del_files_sql = "select picture1, picture2, picture3, picture4
								from story 
								where id = $story";

		$result = mysql_query($del_files_sql);
		if($result){
					while ($pic = mysql_fetch_array($result, MYSQL_ASSOC)) {
				//while(list($key, $value) = each($pic)){//for debug
				//echo "key = ".$key." value = ".$value."<br>";
				//}
					//$i=0;
					//while($i < (count($pic)-1)){
					for($i=1; $i<(count($pic)+1); $i++){
						echo "picture".$i." = ".$pic[picture.$i]."<br>";

							if(is_null($pic[picture.$i])){
							echo $pic[picture.$i]." is NULL <br>";
							//$i++; //note only use $i++ here when using while loop
							 continue;
							}else{
							$del_file = unlink($pic[picture.$i]);
								if ($del_file){
								$status .= "<p>Deleted file ".$pic[picture.$i]." successfully</p>\n";
								}else{
								$status .= "<p>Can't delete file ".$pic[picture.$i].", please try again later</p>\n";
								}
							}
						//$i++;
					}

			}#end while 

			$del_dir = rmdir($the_path."/".$story);
			if ($del_dir){
				$status .= "<p>Deleted directory ".$the_path."/".$story." successfully</p>\n";
				}else{
				$status .= "<p>Can't delete directory ".$the_path."/".$story.", please try again later</p>\n";
				}

===========================================

BTW - Should I use continue 1, when nesting a for loop inside a while loop, how does this work , the manual suggests that this will skip the outer loop and jump to the end? (or beginning) of the nested loop.

Cheers

Synfield :o

Weedpacket

Originally posted by synfield

BTW - Should I use continue 1, when nesting a for loop inside a while loop, how does this work , the manual suggests that this will skip the outer loop and jump to the end? (or beginning) of the nested loop.

continue; and continue 1; are synonyms. The number shows how many loops (or switches) to skip (if statements are ignored):

while
{   // section A
    for
    {   // section B
        continue; // skips section C
        // section C
    }
    // section D
}

while
{   // section A
    for
    {   // section B
        continue 2; // skips sections C and D
        // section C
    }
    // section D
}

Difference between continue and break is that the latter aborts the entire loop, while the former only aborts the current iteration of the loop:

while/for
{
    ...
    continue/break;
    ...
//<-----continue jumps to here
}
//<-----break jumps to here

synfield

Weedpacket, thanks for clarifying that, if you don't come from a programming background like myself, these fundamentals aren't always clear, even in the holy php bible (the manual).

Cheers

Synfield
🙂