PHP string comparison function_PHP tutorial

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The most common way to compare whether two strings are equal is to use "===" to judge. As for the difference between it and "==", simply put, the former emphasizes that the "identical" type also requires the same; the latter If the user requires "equal", the same value is enough, refer to [1]. Or use strcmp to judge, but this can tell you whether the two strings are equal, but it cannot tell you where they are different. My idea is to divide a single string into letters (characters), so that the comparison can accurately know where the difference is. To separate strings, just use "str_split". For syntax, refer to [2]. Then output the result array. The advantage is that even spaces will be used as elements of the array. My previous example was because the first string contained 2 spaces, while the latter one only had one. But the display you see when outputting is the same. You can also split according to other delimiters, such as "explode" or "preg_split",

Generally, you can use !=, == to compare whether two objects are equal. The reason why they are two objects is because they are not necessarily all strings, they can also be integers, etc. For example

$a = "joe";
$b = "jerry";
if ($a != $b)
{
echo "Not equal";
}
else
{
echo "Equal";
}

If you use !==,=== (you can see an extra equal sign) for comparison, the types of the two objects must be strictly equal to return true; otherwise, use ==,!=, the string will be automatically Convert to the corresponding type for comparison.

22 == "22"; // returns true
22 === "22"; // return false

Because of this, some unexpected "accidents" often occur in our programs:

0 == "I love you"; // returns true
1 == "1 I love you";//return true

There is a set of functions for string comparison in the PHP tutorial: strcmp, strcasecmp, strncasecmp(), strncmp(). If the former is greater than the latter, they will return an integer greater than 0; if the former If it is smaller than the latter, an integer less than 0 is returned; if the two are equal, 0 is returned. The principles of their comparison are the same as the rules of other languages.

strcmp is for case-sensitive (i.e. case-sensitive) string comparison:
echo strcmp("abcdd", "abcde"); // Returns 1 (>0), comparing "b" and "b"

strcasecmp for case-insensitive string comparison:
echo strcasecmp("abcdd", "abcde"); // Returns -1 (<0), comparing "d" and "e"

strncmp is used to compare part of a string, starting from the beginning of the string. The third parameter is the length to be compared:
echo strncmp("abcdd", "abcde", 3); // returns 1 (>0), comparing abc and abc

strncasecmp is used to compare part of a string in a case-insensitive manner, starting from the beginning of the string. The third parameter is the length to be compared:
echo strncasecmp("abcdd", "abcde", 3); // Returns 0, comparing abc and abc, which are the same since they are not case-sensitive.

Another situation is that simply comparing the string sizes cannot meet our predetermined needs. For example, normally 10.gif will be larger than 5.gif, but if you apply the above functions, -1 will be returned, that is Indicates that 10.gif is better than 5.gif. For this situation, PHP provides two natural contrast functions strnatcmp and strnatcasecmp:

echo strnatcmp("10.gif", "5.gif"); // returns 1 (>0)
echo strnatcasecmp("10.gif", "5.gif"); // Return 1 (>0)