Summary of the use of PHP string comparison functions strcmp() and strcasecmp(), strcmpstrcasecmp_PHP tutorial

Summary on the use of PHP string comparison functions strcmp() and strcasecmp(), strcmpstrcasecmp

Comparing strings is one of the important features in the string processing capabilities of any programming language. In addition to using comparison operators (==, < or >) for comparison, PHP also provides a series of comparison functions that allow PHP to perform more complex string comparisons. Functions such as strcmp(), strcasecmp() and strnatcmp().

1. String comparison in byte order

To compare strings in byte order, you can use the two functions strcmp() and strcasecmp(). The function strcasecmp() can ignore the case of letters in the string for comparison. The prototypes of these two functions are as follows:

Copy code The code is as follows:

in strcmp(string str1,string str2) //Compare letters in strings case-sensitively
int strcasecmp(string str1,string str2) //Ignore the case comparison of letters in strings

The usage of these two functions is similar, and both need to pass in two string parameters for comparison. You can compare the input strings str1 and str2 starting from the first byte of the two strings according to the ASCII value of the bytes. If they are equal, the comparison will proceed to the next byte until the comparison is completed. Returns one of the following three values:
★If str1 is equal to str2, 0 is returned.
★If str1 is greater than str2, return 1.
★If str1 is less than str2, return -1.
In the following program, the size of two compared strings is determined by the returned value after comparison. Use the strcmp() function to differentiate between upper and lower case letters in a string, and use the strcasecmp() function to ignore case comparisons of letters in a string. Of course it has no practical meaning. The code looks like this:

Copy code The code is as follows:

$username = "Admin";
$password = "lampBrother";

//Case-insensitive comparison, if two strings are equal, return 0
if(strcasecmp($userName,"admin")== 0){
echo "Username exists";
}
//After converting the corresponding functions of the two compared strings into all uppercase or all lowercase, case-insensitive comparison can also be achieved
if(strcasecmp(strtolower($userName),strtolower("admin")) == 0){
echo "Username exists";
}

//Compare case-sensitive letters in strings
switch(strcmp($password,"lampbrother")){
case 0:
echo "The two strings are equal
"; break;
case 1:
echo "The first string is greater than the second string
"; break;
case -1:
echo "The first string is less than the second string
"; break;
}
?>

2. String comparison according to natural ordering

In addition to comparing according to the dictionary order of bytes, PHP also provides comparison of strings according to the "natural sorting" method. The so-called natural sorting refers to sorting according to people's thinking habits in daily life, that is, comparing the numerical parts in the string according to the numerical size. For example, "4" is greater than "33" when compared by bytes, because "4" is greater than the first character in "33", and according to the natural sorting rule, "33" is greater than "4". Use the strnatcmp() function to compare two strings in natural sorting. This function is case-sensitive and its usage format is similar to the strcmp() function.

In the following example, bubble sort is used to sort file names with numbers in an array through two comparison methods. The code looks like this:

Copy code The code is as follows:

//Define an array containing numeric values ​​
$files = array("file11.txt","file22.txt","file1.txt","file2.txt");

function mySort($arr,$select = false){
for($i=0;$i for($j;$j ​​​​ //If the second parameter is true, use the strcmp() function to compare the size
                if($select){
                  // If the comparison result of the two values ​​​​is greater than 0, the positions are swapped
If(strcmp($arr[$j],$arr[j+1])>0){
                           $tmp = $arr[$j];
                       $arr[$j] = $arr[$j+1];
                        $arr[$j+1] = $tmp;
                }
//If the second parameter is false, use the strnatcmp() function to compare the size
              }else{
                   // If the comparison result is greater than 0, swap positions
If(strnatcmp($arr[$j],$arr[$j+1])>0){
                           $tmp = $arr[$j];
                       $arr[$j] = $arr[$j+1];
                          $arr[$j+1]; = $tmp;
                }
            }
        }
}
return $arr; //sorted array
}
print_r(mySort($files,true)); //Select to sort in dictionary order: file1.txt file11.txt file2.txt file22.txt
print_r(mySort($files,false)); //Select to sort in natural order: file1.txt file2.txt file11.txt file22.txt
?>

PHP also provides a case-ignoring version of this function. The strnatcasecmp() function is used in the same way as the strnatcmp() function.

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