Regular expression in C language detecting non word characters - c

Question

I am trying to create a script to detect "not correct" characters on a username. I think the best solution is to apply regex. I have created a sample script for this purpose but I can not find the correct combination for detecting the "bad/faulty" characters.
Update: The regex expression that I am using I found it on Wikipedia Regular expressions
Sample of code:
#include <stdio.h> /* stderr, stdout */
#include <string.h> /* stncpy, strncat etc. */
#include <stdlib.h> /* memory allocation, process control etc. */
#include <sys/types.h>
#include <regex.h>
#define tofind "[^A-Za-z0-9_] $" /* Non word characters */
#define MAX_USERS 4
#define MAX_CHARACTERS 20
typedef struct rec {
char users[MAX_USERS][MAX_CHARACTERS];
}TEMPORARY;
int main (void) {
regex_t regex;
int reti , i;
TEMPORARY *ptr_record;
ptr_record = (TEMPORARY *) malloc (sizeof(TEMPORARY));
if (ptr_record == NULL) {
printf("Out of memmory!\nExit!\n");
exit(0);
}
printf("Sizeof users: %li\n",sizeof(*ptr_record).users);
/* Compile regular expression */
reti = regcomp(&regex, tofind, REG_EXTENDED);
if( reti ){ fprintf(stderr, "Could not compile regex\n"); exit(1); }
for(i = 0; i < MAX_USERS; i++) {
printf("Enter username[%i]:\n",i);
scanf( " %[^\n]" , (*ptr_record).users[i] );
/* Execute regular expression */
reti = regexec(&regex, (*ptr_record).users[i], 0, NULL, 0);
if( !reti ){
puts("Match");
}
else if( reti == REG_NOMATCH ){
puts("No match");
}
else{
regerror(reti, &regex, (*ptr_record).users[i], sizeof((*ptr_record).users));
fprintf(stderr, "Regex match failed: %s\n", (*ptr_record).users[i]);
exit(1);
}
}
/* Free compiled regular expression if you want to use the regex_t again */
regfree(&regex);
for(i = 0; i < MAX_USERS; i++) {
printf("Username[%i][%s]:\n",i,(*ptr_record).users[i]);
}
return 0;
}
Update 2: Input and Output of the code:
Enter username[0]:
Th#nos
No match
Enter username[1]:
t#est
No match
Enter username[2]:
!anotherT$est
No match
Enter username[3]:
S%mple
No match
Username[0][Th#nos]:
Username[1][t#est]:
Username[2][!anotherT$est]:
Username[3][S%mple]:
I thought that all these inputs would be detected by the regular expression and produce a non match.

Answer 1

Answer to the specific question: Finally after some experimentation I understood what I was doing wrong. My regex was not correctly defined. So at the specific task that I want to apply, the correct regex would be "[^A-Za-z0-9_]" instead of "[^A-Za-z0-9_] $". It works perfectly sample of output:
Enter username[0]:
thanos
No match
Enter username[1]:
thanos test
Match
Enter username[2]:
th#no
Match
Enter username[3]:
test
No match
Username[0][thanos]:
Username[1][thanos test]:
Username[2][th#no]:
Username[3][test]: