PHP：使用Goto的正当理由？

Question

I know that the goto statement is frowned upon but I wanted to know if the following situation would make it the most acceptable.

I want to create a unique random number for a column value but to do that I need to create a random number and check to see if it exists in a table.

a:
$rnumber = rand(1, 10);
$queryresult = $mysqli->query("SELECT uniquerandomcolumn FROM tbldata WHERE uniquerandomcolumn =" . $rnumber);

if ($queryresult->num_rows > 0) //if random number exists a row would be returned
{goto a;}  //try again
else {//insert into table}

Answer 1

请改用此号码，这样号码将是唯一的

$id = uniqid(rand(), true);

Answer 2

You don't need goto for that.

do
{
    $rnumber = rand(1, 10);
    $queryresult = $mysqli->query("SELECT uniquerandomcolumn FROM tbldata WHERE uniquerandomcolumn =" . $rnumber);
}
while($queryresult->num_rows > 0);
//insert into table}

EDIT: This answer is just to prove that goto isn't necessary in the original code. In this particular example, I would advise against using this code and use WereWolf - The Alpha's answer in your code.

Answer 3

Instead, you should use a while loop, that counts retry attempts:

$attempt = 0; $success = false;
while ($attempt++ < 3) {
    // ... make sure $success gets marked true!
    // in case of success, make sure you break here!
}
if (!$success) {
    // Failure
}

This makes sure your script never freezes (infinite loop).

Answer 4

The goto statement was mainly - if any - used for error processing: in a long list of statement, each of them being able to trigger an error, a jump (goto) was made near the bottom of the function to skip all the remaining statements, and run a common error processor at the end of the function.

But nowadays, even PHP has exception handling , thus the use of goto is even less justified.

Fix the problem as mentioned

In your case, you can implement a simple algorithm to perform the equivalent function

do {
  $rnumber = rand(1, 10);
  $queryresult = $mysqli->query("SELECT uniquerandomcolumn FROM tbldata WHERE uniquerandomcolumn =" . $rnumber);

} while ($queryresult->num_rows > 0);

having the risk of being in an infinite (or very long) loop...

Room for improvement

Since the number of tries is limited (1 .. 10), it would be better to

• try all numbers from 1 to 10 (maximum) once without repetition
• randomly (eg 7 2 3 9 ...)

ie, perform a maximum of 10 tries, and exit if the row does not exist or if all 10 tries have been done. To try randomly from 1 to 10, use the shuffle function to shuffle randomly an array of 1 to 10 elements.

$tries = array();
for ($i=1 ; $i<=10 ; $i++) $tries[] = $i; // create an array (1,2,3,4,5...)

shuffle ($tries); // shuffle the array, eg now $tries is (8,2,9,1,7...)

$index = 0; // start with first element of $tries
do {
  $rnumber = $tries[$index++];
  $queryresult = $mysqli->query("SELECT uniquerandomcolumn FROM tbldata WHERE uniquerandomcolumn =" . $rnumber);

} while ($queryresult->num_rows > 0 && $tries < 10);

This way you try randomly all 10 possible values, not more.

After the while add

if ($queryresult->num_rows < 1) {
  // found a non existing number: $tries[$index-1]
}
else {
  // all 10 numbers exist in the DB...
}

to deal with the two conditions.

Answer 5

goto isn't a good coding practice, it will make your code unaccountable and unmanageable. Don't ever use goto . Or else a velociraptor will hit you while you compiling your code.

But it's okay if you are making a console application, it's okay.