How to Check If a String Contains Only Ascii

How to check if a String contains only ASCII?

From Guava 19.0 onward, you may use:

boolean isAscii = CharMatcher.ascii().matchesAllOf(someString);

This uses the matchesAllOf(someString) method which relies on the factory method ascii() rather than the now deprecated ASCII singleton.

Here ASCII includes all ASCII characters including the non-printable characters lower than 0x20 (space) such as tabs, line-feed / return but also BEL with code 0x07 and DEL with code 0x7F.

This code incorrectly uses characters rather than code points, even if code points are indicated in the comments of earlier versions. Fortunately, the characters required to create code point with a value of U+010000 or over uses two surrogate characters with a value outside of the ASCII range. So the method still succeeds in testing for ASCII, even for strings containing emoji's.

For earlier Guava versions without the ascii() method you may write:

boolean isAscii = CharMatcher.ASCII.matchesAllOf(someString);

Check that a string contains only ASCII characters?

In Python 3.7 were added methods which do what you want:

str, bytes, and bytearray gained support for the new isascii() method, which can be used to test if a string or bytes contain only the ASCII characters.

---

Otherwise:

>>> all(ord(char) < 128 for char in 'string')
True
>>> all(ord(char) < 128 for char in 'строка')
False

Another version:

>>> def is_ascii(text):
    if isinstance(text, unicode):
        try:
            text.encode('ascii')
        except UnicodeEncodeError:
            return False
    else:
        try:
            text.decode('ascii')
        except UnicodeDecodeError:
            return False
    return True
... 
>>> is_ascii('text')
True
>>> is_ascii(u'text')
True
>>> is_ascii(u'text-строка')
False
>>> is_ascii('text-строка')
False
>>> is_ascii(u'text-строка'.encode('utf-8'))
False

Match if String contains only ASCII character set

The java code is:

public static boolean isAsciiPrintable(String str) {
  if (str == null) {
      return false;
  }
  int sz = str.length();
  for (int i = 0; i < sz; i++) {
      if (isAsciiPrintable(str.charAt(i)) == false) {
          return false;
      }
  }
  return true;
  }
    public static boolean isAsciiPrintable(char ch) {
  return ch >= 32 && ch < 127;
  }
}

Ref: http://www.java2s.com/Code/Java/Data-Type/ChecksifthestringcontainsonlyASCIIprintablecharacters.htm

Checking a string contains only ASCII characters

In Go, we care about performance, Therefore, we would benchmark your code:

func isASCII(s string) bool {
    for _, c := range s {
        if c > unicode.MaxASCII {
            return false
        }
    }
    return true
}

BenchmarkRange-4    20000000    82.0 ns/op

A faster (better, more idiomatic) version, which avoids unnecessary rune conversions:

func isASCII(s string) bool {
    for i := 0; i < len(s); i++ {
        if s[i] > unicode.MaxASCII {
            return false
        }
    }
    return true
}

BenchmarkIndex-4    30000000    55.4 ns/op

---

ascii_test.go:

package main

import (
    "testing"
    "unicode"
)

func isASCIIRange(s string) bool {
    for _, c := range s {
        if c > unicode.MaxASCII {
            return false
        }
    }
    return true
}

func BenchmarkRange(b *testing.B) {
    str := ascii()
    b.ResetTimer()
    for N := 0; N < b.N; N++ {
        is := isASCIIRange(str)
        if !is {
            b.Fatal("notASCII")
        }
    }
}

func isASCIIIndex(s string) bool {
    for i := 0; i < len(s); i++ {
        if s[i] > unicode.MaxASCII {
            return false
        }
    }
    return true
}

func BenchmarkIndex(b *testing.B) {
    str := ascii()
    b.ResetTimer()
    for N := 0; N < b.N; N++ {
        is := isASCIIIndex(str)
        if !is {
            b.Log("notASCII")
        }
    }
}

func ascii() string {
    byt := make([]byte, unicode.MaxASCII+1)
    for i := range byt {
        byt[i] = byte(i)
    }
    return string(byt)
}

Output:

$ go test ascii_test.go -bench=.
BenchmarkRange-4    20000000    82.0 ns/op
BenchmarkIndex-4    30000000    55.4 ns/op
$

Find out if a string contains only ASCII characters

I think I will go for one of these two

IF CONVERT(str, 'US7ASCII') = str THEN
    DBMS_OUTPUT.PUT_LINE('Pure ASCII');
END IF;

IF ASCIISTR(REPLACE(str, '\', '/')) = REPLACE(str, '\', '/') THEN
    DBMS_OUTPUT.PUT_LINE('Pure ASCII');
END IF;

How to check if a string in Python is in ASCII?

def is_ascii(s):
    return all(ord(c) < 128 for c in s)

How can I tell if a string has any non-ASCII characters in it?

Try with this regex. It tests for all ascii characters that have some meaning in a string, from space 32 to tilde 126:

var ascii = /^[ -~]+$/;

if ( !ascii.test( str ) ) {
  // string has non-ascii characters
}

Edit: with tabs and newlines:

/^[ -~\t\n\r]+$/;

How to find out if there is any non ASCII character in a string with a file path

As suggested by several comments and highlighted by @CrisLuengo answer, we can iterate the characters looking for any in the upper bit set (live example):

#include <iostream>
#include <string>
#include <algorithm>

bool isASCII (const std::string& s)
{
    return !std::any_of(s.begin(), s.end(), [](char c) { 
        return static_cast<unsigned char>(c) > 127; 
    });
}

int main()
{
    std::string s1 { "C:\\Users\\myUser\\Downloads\\Hello my friend.pdf" };   
    std::string s2 { "C:\\Users\\myUser\\Downloads\\ü.pdf" };

    std::cout << std::boolalpha << isASCII(s1) << "\n";
    std::cout << std::boolalpha << isASCII(s2) << "\n";
}

true

false

---

Related Topics