How to check string is alphanumeric or not using Regular Expression

• Last Updated : 18 Nov, 2022

Given string str, the task is to check whether the string is alphanumeric or not by using Regular Expression

An alphanumeric string is a string that contains only alphabets from a-z, A-Z and some numbers from 0-9.

Examples:

Input: str = “GeeksforGeeks123”
Output: true
Explanation:
This string contains all the alphabets from a-z, A-Z, and the number from 0-9. Therefore, it is an alphanumeric string.
Input: str = “GeeksforGeeks”
Output: false
Explanation:
This string contains all the alphabets from a-z, A-Z, but doesn’t contain any number from 0-9. Therefore, it is not an alphanumeric string.
Input: str = “GeeksforGeeks123@#”
Output: false
Explanation:
This string contains all the alphabets from a-z, A-Z, and the number from 0-9 along with some special symbols. Therefore, it is not an alphanumeric string.

Approach: This problem can be solved by using Regular Expression.

• Get the string.
• Create a regular expression to check string is alphanumeric or not as mentioned below:
`regex = "^(?=.*[a-zA-Z])(?=.*[0-9])[A-Za-z0-9]+\$";`
• Where:
• ^ represents the starting of the string
• (?=.*[a-zA-Z]) represents the alphabets from a-z, A-Z
• (?=.*[0-9]) represents any number from 0-9
• [A-Za-z0-9] represents whether everything is either alphabetical or digit
• + represents one or more times
• \$ represents the ending of the string
• Match the given string with the regex, in Java, this can be done by using Pattern.matcher()
• Return true if the string matches with the given regex, else return false

Below is the implementation of the above approach.

C++

 `// C++ program to check` `// String is alphanumeric or not using Regular Expression``#include ``#include ` `using` `namespace` `std;` `// Function to validate the // String is alphanumeric or not using Regular Expression``bool` `isAlphaNumeric(string str) {` `// Regex to check valid  alphanumeric String.``  ``const` `regex pattern(``"^(?=.*[a-zA-Z])(?=.*[0-9])[A-Za-z0-9]+\$"``);` `// If the string` `// is empty return false``  ``if` `(str.empty())``  ``{``    ``return` `false``;``  ``}`  `// Return true if the String` `// matched the ReGex` `if` `(regex_match(str, pattern))``{``return` `true``;;``}``else``{``  ``return` `false``;``}``}` `// Driver Code` `int` `main()` `{``  ``// Test Case 1:``string str1= ``"GeeksforGeeks123"``;``cout <

Java

 `// Java program to check string is``// alphanumeric or not using Regular Expression.` `import` `java.util.regex.*;` `class` `GFG {` `    ``// Function to check string is alphanumeric or not``    ``public` `static` `boolean` `isAlphaNumeric(String str)``    ``{``        ``// Regex to check string is alphanumeric or not.``        ``String regex = ``"^(?=.*[a-zA-Z])(?=.*[0-9])[A-Za-z0-9]+\$"``;` `        ``// Compile the ReGex``        ``Pattern p = Pattern.compile(regex);` `        ``// If the string is empty``        ``// return false``        ``if` `(str == ``null``) {``            ``return` `false``;``        ``}` `        ``// Pattern class contains matcher() method``        ``// to find matching between given string``        ``// and regular expression.``        ``Matcher m = p.matcher(str);` `        ``// Return if the string``        ``// matched the ReGex``        ``return` `m.matches();``    ``}` `    ``// Driver Code.``    ``public` `static` `void` `main(String args[])``    ``{` `        ``// Test Case 1:``        ``String str1 = ``"GeeksforGeeks123"``;``        ``System.out.println(``            ``str1 + ``": "``            ``+ isAlphaNumeric(str1));` `        ``// Test Case 2:``        ``String str2 = ``"GeeksforGeeks"``;``        ``System.out.println(``            ``str2 + ``": "``            ``+ isAlphaNumeric(str2));` `        ``// Test Case 3:``        ``String str3 = ``"GeeksforGeeks123@#"``;``        ``System.out.println(``            ``str3 + ``": "``            ``+ isAlphaNumeric(str3));` `        ``// Test Case 4:``        ``String str4 = ``"123"``;``        ``System.out.println(``            ``str4 + ``": "``            ``+ isAlphaNumeric(str4));` `        ``// Test Case 5:``        ``String str5 = ``"@#"``;``        ``System.out.println(``            ``str5 + ``": "``            ``+ isAlphaNumeric(str5));``    ``}``}`

Python3

 `# Python3 program to check``# string is alphanumeric or``# not using Regular Expression.``import` `re` `# Function to check string``# is alphanumeric or not``def` `isAlphaNumeric(``str``):` `    ``# Regex to check string is``    ``# alphanumeric or not.``    ``regex ``=` `"^(?=.*[a-zA-Z])(?=.*[0-9])[A-Za-z0-9]+\$"` `    ``# Compile the ReGex``    ``p ``=` `re.``compile``(regex)` `    ``# If the string is empty``    ``# return false``    ``if``(``str` `=``=` `None``):``        ``return` `False` `    ``# Return if the string``    ``# matched the ReGex``    ``if``(re.search(p, ``str``)):``        ``return` `True``    ``else``:``        ``return` `False` `# Driver Code` `# Test Case 1:``str1 ``=` `"GeeksforGeeks123"``print``(str1, ``":"``,``      ``isAlphaNumeric(str1))` `# Test Case 2:``str2 ``=` `"GeeksforGeeks"``print``(str2, ``":"``,``      ``isAlphaNumeric(str2))` `# Test Case 3:``str3 ``=` `"GeeksforGeeks123@#"``print``(str3, ``":"``,``      ``isAlphaNumeric(str3))` `# Test Case 4:``str4 ``=` `"123"``print``(str4, ``":"``,``      ``isAlphaNumeric(str4))` `# Test Case 5:``str5 ``=` `"@#"``print``(str5, ``":"``,``      ``isAlphaNumeric(str5))` `# This code is contributed by avanitrachhadiya2155`

Output:

```GeeksforGeeks123: true
GeeksforGeeks: false
GeeksforGeeks123@#: false
123: false
@#: false```

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