供应代码正则表达式

Question

I'm trying to develop a C code that checks the validity of "Provisioning code" string using regular expressions. A "provisioning code" format should respect the following law:

If not an empty string, this argument SHOULD be in the form of a hierarchical descriptor with one or more nodes specified. Each node in the hierarchy is represented as a 4-character sub-string, containing only numerals or upper-case letters. If there is more than one node indicated, each node is separated by a "." (dot). Examples: "TLCO" or "TLCO.GRP2".

I started development using the code in this link http://web.archive.org/web/20160308115653/http://peope.net/old/regex.html

#include <sys/types.h>
#include <regex.h>
#include <stdio.h>

int main(int argc, char *argv[]){
    regex_t regex;
    int reti;
    char msgbuf[100];

/* Compile regular expression */
    reti = regcomp(&regex, "^a[[:alnum:]]", 0);
    if( reti ){ fprintf(stderr, "Could not compile regex\n"); exit(1); }

/* Execute regular expression */
    reti = regexec(&regex, "abc", 0, NULL, 0);
    if( !reti ){
            puts("Match");
    }
    else if( reti == REG_NOMATCH ){
            puts("No match");
    }
    else{
            regerror(reti, &regex, msgbuf, sizeof(msgbuf));
            fprintf(stderr, "Regex match failed: %s\n", msgbuf);
            exit(1);
    }

/* Free compiled regular expression if you want to use the regex_t again */
    regfree(&regex);

    return 0;
}

this code works fine but my problem is what's the best regular expression that should be input of the function regcomp.

I started to try with a regular expression that matches with string that contains exactly 4 characters uppercases or numerals that means example like TLCO or TLC2 trying with the regular expression "[A-Z0-9]{4}" but I get "No match" as output with matches examples like TLC2.

Is there a suggestion about the right regular expression that should be input of regcomp and matches with "provisioning code"?

Answer 1

You may use the following regex that will work alright if you also pass REG_EXTENDED flag to the regcomp method (for the $ and {m,n} modifier to work correctly):

^[A-Z0-9]{4}([.][A-Z0-9]{4})*$

C code:

reti = regcomp(&regex, "^[A-Z0-9]{4}([.][A-Z0-9]{4})*$", REG_EXTENDED);

Details

• ^ - start of string
• [A-Z0-9]{4} - 4 uppercase ASCII letters or digits
• ([.][A-Z0-9]{4})* - zero or more sequences of:
  • [.] - a literal . char
  • [A-Z0-9]{4} - 4 uppercase ASCII letters or digits
• $ - end of string.