Can't find a solution to this which seems simple enough. I have user input field and want to check the user has prefixed the code asked for with an S (example code S123456 so I want to check to make sure they didn't just put 123456).
// Function to check string starting with s
if (isset($_REQUEST['submitted'])) { $string=$_POST['required_code'];function startsWith ($string, $startString){$len = strlen($startString);return (substr($string, 0, $len) === $startString);
}
// Do the check
if(startsWith($string, "s"))echo "Code starts with a s";else echo "Code does not start with a s";}
The problem is if the user inputs an upper case S this is seen as not being a lower case s.
So I can get round this using
$string = strtolower($string);
So if the user inputs an uppercase S it gets converted to lower case before the check. But is this the best way? Is there not someway to say S OR s?
Any suggestions?
What you could do instead of creating your own function, is using stripos. Stripos tries to find the first occurrence of a case-insensitive substring.
So as check you could have:
if(stripos($string, "s") === 0)
You need 3 equal signs, since stripos will return false (0) if it can't find the substring.
Take your pick; there are many ways to see if a string starts with 'S'. Some of them case-sensitive, some not. The options below should all work, although I wouldn't consider any of them better than your current solution. stripos() is probably the 'cleanest' check though. If you need multibyte support, there's also the mb_stripos() variant.
(Although; keep in mind that stripos() can also return false. If you're going with that option, always use the stricter "identical" operator ===, instead of == to prevent type juggling.)
if (stripos($string, 's') === 0) {
// String starts with S or s
} else {
// It does not
}
if (str_starts_with($string, 's') || str_starts_with($string, 'S')) // ...
if (in_array(substr($string, 0, 1), ['S', 's'], true)) // ...
if (preg_match('/^s/i', $string)) // ...
// Many other regexp patterns also work
Thanks all, it was
if (str_starts_with($string, 's') || str_starts_with($string, 'S')) // ...
I was looking for I had tried
if (str_starts_with($string, 's' || 'S')) // ...
Related
I was asked on an interview what would be the fastest way to extract the comparison operator between two statements.
For example rate>=4 the comparison operator is '>=' it should be able to extract '>','<','!=','=','<=','>=','='
The function must return the comparison operator.
This is what I wrote, and they marked it as wrong.
function extractcomp($str)
{
$temp = [];
$matches = array('>','<','!','=');
foreach($matches as $match)
{
if(strpos($str,$match)!== false)
{
$temp[] = $match;
}
}
return implode('',$temp);
}
Does anyone have a better way?
you can read character by character once you hit the first occurrence you can determine what's gonna be the next character i.e.:
$ops = ['>','<','!','='];
$str = "rate!=4";
foreach($ops as $op)
{
if(($c1 = strpos($str, $op)) !== false)
{
$c2 = $str[$c1++] . (($str[$c1] == $ops[3]) ? $str[$c1] : "");
break;
}
}
echo $c2;
So if the first search character is ">" you can only assume the 2nd one is gonna be "=" or it doesn't exist. So you get the index of 1st character and increment it and check if the 2nd character exists in our search array or not. Then return the value. this will loop until it finds the 1st occurrence then breaks.
EDIT:
here's another solution:
$str = "rate!=4";
$arr = array_intersect(str_split($str), ['>','<','=','!']);
echo current($arr).(end($arr) ? end($arr) : '');
not as fast as the loop but definitely decreases the bloat code.
There's always a better way to optimize the code.
Unless they have some monkeywrenching strings to throw at this custom function, I recommend trim() with a ranged character mask. Something like echo trim('rate>=4',"A..Za..z0..9"); would work for your sample input in roughly half the time.
Code: (Demo)
function extractcomp($str){
return trim($str,"A..Za..z0..9");
}
echo extractcomp("rate>=4");
Regarding regex, better efficiency in terms of step count with preg_match() would be to use a character class to match the operators.
Assuming only valid operators will be used, you can use /[><!=]+/ or if you want to tighen up length /[><!=]{1,3}/
Just 8 steps on your sample input string. Demo
This is less strict than Andreas' | based pattern, but takes fewer steps.
It depends on how strict the pattern must be. My pattern will match !==.
If you want to improve your loop method, write a break after you have matched the entire comparison operator.
Actually, you are looping the operators. That would have been their issue (or one of them). Your method will not match ==. I'm not sure if that is a possible comparison (it is not in your list).
I tried to add extra security by removing special characters. I want to allow letters, numbers and ? = & only.
I tried:
if (strpos($_SERVER['REQUEST_URI'],'\'')) { echo 'true'; }
I cannot just simply put ' in between the '' as it breaks it so I tried adding the \ but it didn't work.
Is there a way to detect all the symbols in the url string or input field?
EDIT:
tried adding < simply into the list
if (preg_match('#[#*,!$\'\-;:<>~`^|\(\\)\\{\\}\\[\\]]#i', $_SERVER['REQUEST_URI']) || strpos($_SERVER['REQUEST_URI'],'script')) {
echo 'Cannot do that';
}
I tried adding ([\<])([^\>]{1,})*([\>]) into there but it didn't work.
I also tried adding a condition if strcmp($_SERVER['REQUEST_URI'], strip_tags($_SERVER['REQUEST_URI'])) != 0
and when i added into the url, it didn't do anything
Use preg_match to test for anything but the characters you want:
if (preg_match('#[^a-z0-9?=&]#i', $str)) { echo 'true'; }
Use preg_replace to remove them:
$str = preg_replace('#[^a-z0-9?=&]#i', '', $str);
If you just want to prohibit certain characters, use a regular expression that just matches those characters:
if (preg_match('#[\'\-;:~`]#i', $str)) { echo 'true'; }
You can fix that using double quotes as strings delimiter, try this
if (strpos($_SERVER['REQUEST_URI'],"'")) { echo 'true'; }
One thing that none of the posts addressed is why strpos didn't work for you. strpos can return two types. It can return an integer that is greater than or equal to zero. 0 being the first character. It can also return a boolean type false. To check if if strpos found a match it would have to have been written like this:
if (strpos($_SERVER['REQUEST_URI'],'\'') !== false) { echo 'true'; }
From the PHP Documentation The comparison $a !== $b operator works this way:
return TRUE if $a is not equal to $b, or they are not of the same type.
Information on strpos returning two types (boolean false or an integer) can be found in this PHP strpos Documentation. In particular:
Returns the position of where the needle exists relative to the beginning of the haystack string (independent of offset). Also note that string positions start at 0, and not 1.
Returns FALSE if the needle was not found.
So as you can see 0 and false are not the same thing which is why your test failed.
As for security and strings in PHP I recommend you look at this StackOverflow article for some opinions on the matter.
I would like to know what is the best way to know if my substring is in the string.
So, I can has these kind of value :
"abcd.tif"
"abcd_A.tif"
"abcd_B.tif"
"abcd_VP.tif"
I would detect if "_A" or "_B" or "_VP" is present in the string.
What's the best way ? Using a combination of substr and strlen ?
or use regex ?
Use strpos, which will give you the 0-indexed position of the needle in the string. If it's not in the string, strpos returns false. (There is also case-insensitive stripos).
However, you can only check one needle at a time. If you'd like to check for any of the three simultaneously you can either use a loop or write the terser but less efficient way:
preg_match('/_A|_B|_VP/', $str)
...which will return true if any of those three strings matches.
The most efficient way (I know of :P) is strpos.
$s = 'abcd_VP.tif';
if (strpos('_A', $s) !== false) {
// do your thing
}
You can do a simple || after this, it won't be as short, but it will be much quicker than regex:
$s = 'abcd_VP.tif';
if ((strpos('_A', $s) !== false) || (strpos('_B', $s) !== false) || (strpos('_VP') !== false)) {
// do your thing
}
Use OR operation like (_A)|(_VP) etc. check this question as a hint: Regular Expressions: Is there an AND operator? , to use 'OR' in regular expression.
How do i make a if statement which checks if the string contains a forward slash?
$string = "Test/Test";
if($string .......)
{
mysql_query("");
}
else
{
echo "the value contains a invalid character";
}
You can use strpos, which will make sure there is a forward slash in the string but you need to run it through an equation to make sure it's not false. Here you can use strstr(). Its short and simple code, and gets the job done!
if(strstr($string, '/')){
//....
}
For those who live and die by the manual, when the haystack is very large, or the needle is very small, it is quicker to use strstr(), despite what the manual says.
Example:
Using strpos(): 0.00043487548828125
Using strstr(): 0.00023317337036133
if(strpos($string, '/') !== false) {
// string contains /
}
From the PHP manual of strstr:
Note:
If you only want to determine if a particular needle occurs within
haystack, use the faster and less memory intensive function strpos()
instead.
Use strpos()
If it doesn't return false, the character was matched.
I compared strpos() results with 0. Somehow comparison with false did not work for me.
if (strpos($t, '/') !== 0) {
echo "No forward slash!";
}
This question already has answers here:
How do I check if a string contains a specific word?
(36 answers)
Closed 26 days ago.
In SQL we have NOT LIKE %string%
I need to do this in PHP.
if ($string NOT LIKE %word%) { do something }
I think that can be done with strpos()
But can’t figure out how…
I need exactly that comparission sentence in valid PHP.
if ($string NOT LIKE %word%) { do something }
if (strpos($string, $word) === FALSE) {
... not found ...
}
Note that strpos() is case sensitive, if you want a case-insensitive search, use stripos() instead.
Also note the ===, forcing a strict equality test. strpos CAN return a valid 0 if the 'needle' string is at the start of the 'haystack'. By forcing a check for an actual boolean false (aka 0), you eliminate that false positive.
Use strpos. If the string is not found it returns false, otherwise something that is not false. Be sure to use a type-safe comparison (===) as 0 may be returned and it is a falsy value:
if (strpos($string, $substring) === false) {
// substring is not found in string
}
if (strpos($string, $substring2) !== false) {
// substring2 is found in string
}
use
if(stripos($str,'job')){
// do your work
}
<?php
// Use this function and Pass Mixed string and what you want to search in mixed string.
// For Example :
$mixedStr = "hello world. This is john duvey";
$searchStr= "john";
if(strpos($mixedStr,$searchStr)) {
echo "Your string here";
}else {
echo "String not here";
}
Kind of depends on your data, doesn't it? strpos('a foolish idea','fool') will show a match, but may not be what you want. If dealing with words, perhaps
preg_match("!\b$word\b!i",$sentence)
is wiser. Just a thought.