How do I check if a string doesn't exist and then return false?

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I'm trying to make my code return false if the $str doesn't exist

Here is what I tried (but didn't work):

function rev_epur_str($str)
{
    $str = implode(' ', array_map('strrev', explode(' ', $str)));
    $str = preg_replace('/\s+/', '', $str);
    if (isset($str)) 
    {
        return $str;
    }
    else
    {
        return false;
    }
}
var_dump(rev_epur_str());

Output says:

PHP Warning:  Missing argument 1 for rev_epur_str() 

It just returns an error instead of false

var_dump(rev_epur_str("")); // returns string(0) "" instead of FALSE

How do I return false if $str is empty?


You can in PHP set the default value of a parameter. The code below makes $str an optional parameter and at the same time, it does an empty check to return false.

function rev_epur_str($str = '')
{
    if (empty($str))
      return false;

    $str = implode(' ', array_map('strrev', explode(' ', $str)));
    $str = preg_replace('/\s+/', '', $str);

    return $str;
}

var_dump(rev_epur_str()); // false

var_dump(rev_epur_str('str')); // rts

Note: The error shown in your original code is completely valid, you have set that your function takes a parameter therefore you must pass a parameter to it, that is, unless you use a default value for said parameter (which is what has been done above).

Live Example

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Reading Material

Default Arguments

How to check if String contains another SubString in , How do you check if all characters in a string are the same? string.find(i) returns the index of where the substr i begins in st, or -1 on failure. This is the most intuitive answer in my opinion, you can make this probably into a 1 liner, but I'm not a big fan of those usually. This gives the extra value of knowing where the substring is found in the string.


Instead of returning a boolean, echo string, so you can be sure if its working fine:

function rev_epur_str($str)
{
    $str = implode(' ', array_map('strrev', explode(' ', $str)));
    $str = preg_replace('/\s+/', '', $str);
    if (isset($str)) 
    {
        echo $str;
    }
    else
    {
        echo 'false';
    }
}

How to Check If a String Contains a Specific Word in PHP, How do you check if a string does not contain a substring? @stefan ,you are right,there is a find method,but what about split,replace and many other staff.You can compare std::string to the string api in Java.PS:Also I do think contains is much more elegant than find to check if a string contains another string.


You have to call the function like

var_dump(rev_epur_str($str));

Means $str should have some value;

How to Check if a Python String Contains Another String?, How do you check if a string contains a word python? the === is very important, because strpos will return 0 if the word 'are' is at the very beginning of the string, and since 0 loosely equals FALSE, you would be frustrated trying to find out what was wrong. The === operator makes it check very literally if the result was a boolean false and not a 0.


Your code throws an error because you declare an argument to your function and you call it without any.

One way to work around this and allow a call to your function without argument is to declare a default value like this (here with the value NULL):

function rev_epur_str($str = NULL)
{
    //code here
}
rev_epur_str(); //will work

Also, testing isset will only work if the variable never was set or is NULL. If you want it to work with empty string you can try with:

if (empty($str))
{
     return false;
}
//etc

How to check if a string does not contain a specific phrase?, Well, an easy way is to brute force by checking if the substring exists your next question would be “well what algorithm does Python actually use?” You can use the in operator or the string's find method to check if a string  SQL contains string is used to check if a string contains a substring in SQL Server or not.


How to check if Python string contains another string, The code here: if (strpos($a, 'are') !== false) { // The word WAS found }. Means that the word WAS found in the string. If you remove the NOT  Check if any string that satisfies the condition in checkIfMatch() function exist in List result = any ( checkIfMatch for elem in listOfStrings ) Complete example is as follows,


Python: Check if String Contains Substring, If it does, the method returns the starting index of a substring within the string; otherwise it returns -1. Syntax. The general syntax is : string.find(substring). Checks that the String does not contain certain characters. : String vs Char Array « Data Type « Java Tutorial


JavaScript: Check if String Contains a Substring, If find doesn't find a match, it returns -1, otherwise it returns the left-most index of the substring in the larger string. fullstring = "StackAbuse" substring = "tack" if  Normally, when you have objects, you check if they have something by just use [] or .: if string.sub then -- There is a `sub` in the `string` library! end if string["sub"] ~= nil then -- This is the same end if not string.sub == nil then -- This is the same, too end