Code Golf: Email Address Validation without Regular Expressions

Asked 2009-09-07T17:25:29.300

(Edit: What is Code Golf: Code Golf are challenges to solve a specific problem with the shortest amount of code by character count in whichever language you prefer. More info here on Meta StackOverflow. )

Code Golfers, here's a challenge on string operations.

Email Address Validation, but without regular expressions (or similar parsing library) of course. It's not so much about the email addresses but how short you can write the different string operations and constraints given below.

The rules are the following (yes, I know, this is not RFC compliant, but these are going to be the 5 rules for this challenge):

At least 1 character out of this group before the @:
```
A-Z, a-z, 0-9, . (period), _ (underscore)
```
@ has to exist, exactly one time
```
john@smith.com
    ^
```
Period (.) has to exist exactly one time after the @
```
john@smith.com
          ^
```
At least 1 only [A-Z, a-z] character between @ and the following . (period)
```
john@s.com
     ^
```
At least 2 only [A-Z, a-z] characters after the final . period
```
john@smith.ab
           ^^
```

Please post the method/function only, which would take a string (proposed email address) and then return a Boolean result (true/false) depending on the email address being valid (true) or invalid (false).

Samples:
b@w.org    (valid/true)          @w.org     (invalid/false)    
b@c@d.org  (invalid/false)       test@org   (invalid/false)    
test@%.org (invalid/false)       s%p@m.org  (invalid/false)    
j_r@x.c.il (invalid/false)       j_r@x.mil  (valid/true)
r..t@x.tw  (valid/true)          foo@a%.com (inv


                    
                    
                        
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            3 Answers
            
            
                
                    
                        
                            
                            
                        
                        20
                        
                            
                            
                        
                        
                    
                    
                        
                        C89 (166 characters)
#define B(c)isalnum(c)|c==46|c==95
#define C(x)if(!v|*i++-x)return!1;
#define D(x)for(v=0;x(*i);++i)++v;
v;e(char*i){D(B)C(64)D(isalpha)C(46)D(isalpha)return!*i&v>1;}

Not re-entrant, but can be run multiple times.  Test bed:
#include<stdio.h>
#include<assert.h>
main(){
    assert(e("b@w.org"));
    assert(e("r..t@x.tw"));
    assert(e("j_r@x.mil"));
    assert(!e("b@c@d.org"));
    assert(!e("test@%.org"));
    assert(!e("j_r@x.c.il"));
    assert(!e("@w.org"));
    assert(!e("test@org"));
    assert(!e("s%p@m.org"));
    assert(!e("foo@a%.com"));
    puts("success!");
}


                        
                        
                            answered 2009-09-07T18:11:59.770
                            
                        
                        
                            
                                
                                
                            
                        
                        
                            
                            
                            
                                
                                
                            
                            
                        
                    
                
            
            
            
                
                    
                        
                            
                            
                        
                        6
                        
                            
                            
                        
                        
                    
                    
                        
                        C89, 175 characters.

#define G &&*((a+=t+1)-1)==
#define H (t=strspn(a,A
t;e(char*a){char A[66]="_.0123456789Aa";short*s=A+12;for(;++s<A+64;)*s=s[-1]+257;return H))G 64&&H+12))G 46&&H+12))>1 G 0;}


I am using the standard library function strspn(), so I feel this answer isn't as "clean" as strager's answer which does without any library functions.  (I also stole his idea of declaring a global variable without a type!)

One of the tricks here is that by putting . and _ at the start of the string A, it's possible to include or exclude them easily in a strspn() test: when you want to allow them, use strspn(something, A); when you don't, use strspn(something, A+12).  Another is assuming that sizeof (short) == 2 * sizeof (char), and building up the array of valid characters 2 at a time from the "seed" pair Aa.  The rest was just looking for a way to force subexpressions to look similar enough that they could be pulled out into #defined macros.

To make this code more "portable" (heh :-P) you can change the array-building code from

char A[66]="_.0123456789Aa";short*s=A+12;for(;++s<A+64;)*s=s[-1]+257;


to

char*A="_.0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";


for a cost of 5 additional characters.

                        
                        
                            answered 2009-09-07T20:59:54.580
                            
                        
                        
                            
                                
                                
                            
                        
                        
                            
                            
                            
                                
                                
                            
                            
                        
                    
                
            
            
            
                
                    
                        
                            
                            
                        
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                        'Using no regex':
PHP 47 Chars.

<?=filter_var($argv[1],FILTER_VALIDATE_EMAIL);


                        
                        
                            answered 2009-10-26T18:53:24.227
                            
                        
                        
                            
                                
                                
                            
                        
                        
                            
                            
                            
                                
                                
                            
                            
                        
                    
                
            
            
        

        
        
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