How to determine if a string is a pure ASCII string

How to determine if a string is a pure ASCII string:

Method 1: Python Implementation

python
def is_ascii(s):
    try:
        s.encode('ascii')
        return True
    except UnicodeEncodeError:
        return False

# Or use ord() function
def is_ascii_v2(s):
    return all(ord(c) < 128 for c in s)

Method 2: JavaScript Implementation

javascript
function isASCII(str) {
    return /^[\x00-\x7F]*$/.test(str);
}

// Or use codePointAt()
function isASCIIV2(str) {
    for (let i = 0; i < str.length; i++) {
        if (str.codePointAt(i) > 127) {
            return false;
        }
    }
    return true;
}

Method 3: Java Implementation

java
public static boolean isASCII(String str) {
    return str.chars().allMatch(c -> c < 128);
}

// Or use regular expression
public static boolean isASCIIV2(String str) {
    return str.matches("\\A\\p{ASCII}*\\z");
}

Method 4: C/C++ Implementation

c
#include <stdbool.h>
#include <string.h>

bool is_ascii(const char* str) {
    for (size_t i = 0; str[i] != '\0'; i++) {
        if ((unsigned char)str[i] > 127) {
            return false;
        }
    }
    return true;
}

Method 5: Go Implementation

go
func isASCII(s string) bool {
    for _, r := range s {
        if r > 127 {
            return false
        }
    }
    return true
}

Performance Optimization Suggestions:

1. Early termination: Return immediately when non-ASCII character is found
2. Batch checking: Use SIMD instructions to accelerate (C/C++)
3. Cache results: Cache results for repeatedly checked strings
4. Use regular expressions: Suitable for simple scenarios

Important Notes:

• Empty string is considered ASCII string
• Control characters (0-31) are also ASCII
• Pay attention to string encoding format
• Consider Unicode combining characters