C Regex Not Matching - c

Question

I've tested the following regular expression at http://www.regexpal.com/
([A-Z]{1}[a-z]+)+([_]{1}([A-Z]{1}[a-z]+)+)+[.][a-z]+
Which successfully matches the following file names:
Butter_Butter.jpg
JavaPiebald_Java_Piebald.jpg
LowWhitePied_Pied.jpg
Piebald_Piebald.jpg
SpinnerBlast_Spider_Pinstripe_Pastel.jpg
Caramel_Caramel.jpg
LightningPied_Pied_Axanthic.jpg
Pastel_Pastel.jpg
Spider_Spider.jpg
Spinner_Spider_Pinstripe.jpg
When I implement the regular expression in the following C code, I receive no matches:
#define COLLECTION_REGEX "([A-Z]{1}[a-z]+)+([_]{1}([A-Z]{1}[a-z]+)+)+[.][a-z]+"
int is_valid_filename(char *filename)
{
regex_t regex;
int i, match;
char msgbuf[100];
match = 1;
i = regcomp(&regex, COLLECTION_REGEX, 0);
if (i)
{
perror("Could not compile regex");
}
else
{
match = regexec(&regex, filename, 0, NULL, 0);
if (!match)
{
puts("Match");
}
else if (match == REG_NOMATCH)
{
puts("No match");
}
else
{
regerror(match, &regex, msgbuf, sizeof(msgbuf));
puts(msgbuf);
}
}
regfree(&regex);
return match;
}
Subsequent execution:
./a.out
No match
No match
No match
No match
No match
No match
No match
No match
No match
No match
The regular expression appears correct, I am uncertain as to why I am obtaining these results.
Output from GDB:
Breakpoint 1, is_valid_filename (filename=0x609050 "Piebald_Piebald.jpg") at crp-web-builder.c:76
76 match = regexec(&regex, filename, 0, NULL, 0);
(gdb) continue
Continuing.
No match
Breakpoint 1, is_valid_filename (filename=0x609460 "LightningPied_Pied_Axanthic.jpg") at crp-web-builder.c:76
76 match = regexec(&regex, filename, 0, NULL, 0);
(gdb) continue
Continuing.
No match
Breakpoint 1, is_valid_filename (filename=0x609870 "SpinnerBlast_Spider_Pinstripe_Pastel.jpg") at crp-web-builder.c:76
76 match = regexec(&regex, filename, 0, NULL, 0);
(gdb) continue
Continuing.
No match

Answer 1

Thanks to Jonathan Leffler. The line:
i = regcomp(&regex, COLLECTION_REGEX, 0);
Should be:
i = regcomp(&regex, COLLECTION_REGEX, REG_EXTENDED);