If you need Unicode support, your goto library for the real deal is ICU. ICU also has very solid regex support. And while ICU has plenty of documentation, examples on the net sometimes fall short. The following is a simple command line program which will do both regex replacement, matching and capture groups. It also serves as a decent example of how to use the library. ICU is the basis for unicode and regex support in Android and iOS as well. So this little test program will help you there as well.

ICU likes to do everything in UTex, which I think is always UTF-16. So, to do UTF-8 or ASCII you need to conversion. The program converts the UTF-8 on the command line, runs it through the regex and returns.

Usage

Since you are running this on the command line, you need to escape ‘\’ some chars in bash, mainly backslashes and exclamation marks. It will printout the regex it actually used.

Source on gist. (Easier to copy)

$ ./regextest "Hello(.*)" "Hello Bob"
pattern:     -->[Hello(.*)]<--
test on:     -->[Hello Bob]<--
MATCH: string matches regex
Capture group 0: -->[Hello Bob]<--
Capture group 1: -->[ Bob]<--

$ ./regextest "(ftp|http|https):\\/\\/(\\w+:{0,1}\\w*@)?(\\S+)(:[0-9]+)?(\\/|\\/([\\w#\!:.?+=&%@\!\\-\\/]))?" http://www.google.com

pattern:     -->[(ftp|http|https):\/\/(\w+:{0,1}\w*@)?(\S+)(:[0-9]+)?(\/|\/([\w#\!:.?+=&%@\!\-\/]))?]<--
test on:     -->[http://www.google.com]<--
MATCH: string matches regex
Capture group 0: -->[http://www.google.com]<--
Capture group 1: -->[http]<--
Capture group 2: -->[]<--
Capture group 3: -->[www.google.com]<--
Capture group 4: -->[]<--
Capture group 5: -->[]<--
Capture group 6: -->[]<--

Source

// The following code is freeware:
// regextest.c
// Author: ed@wigwag.com
//
// Simple test program for regex using ICU's regex matching.

#include <stdio.h>
#include <getopt.h>
#include <string.h>
#ifdef __cplusplus
#include <cstdlib>
#endif
#include <unicode/regex.h>
#include <unicode/utext.h>
#include <unicode/errorcode.h>
#include <unicode/ucnv.h>
#include <unicode/utypes.h>
#include <unicode/uchar.h>

static const char OptionsInfo[] = "Usage: regextest [-r] \"PATTERN\" \"TEST STRING\"\n"
								  "-r : replace mode -> \"PATTERN\" \"TEST STRING\" \"replacement\"\n"
								  "You need to escape these items like this: \\\" and \\$ b/c of bash.\n"
								  "\n";

/* ICU library libs/programs...
 * http://www.linuxfromscratch.org/blfs/view/svn/general/icu.html
 * http://icu-project.org/download/4.4.html#ICU4C
 *
 */

int main(int argc, char *argv[]) {
	int exitcode = 1;
	bool replace_mode=false;
    int c;
    int digit_optind = 0;

    while (1)
      {
        c = getopt (argc, argv, "r");
        if (c == -1)
        	break;

        switch (c)
          {
          case 'r':
        	  replace_mode = true;
        	  break;
          }
      }

	if(argc-optind < 2) {
		printf("%s",OptionsInfo);
		exit(1);
	}
	if(replace_mode && argc-optind < 3) {
		printf("%s",OptionsInfo);
		exit(1);
	}

	printf("pattern:     -->[%s]<--\n", argv[optind]);
	printf("test on:     -->[%s]<--\n", argv[optind+1]);

	UErrorCode        status    = U_ZERO_ERROR;
	UText *regex1 = NULL;
	UText *matchthis = NULL;

	//	static const char *regex_validate_string = "(?:cp\\:([0-9]+)\\:){0,1}\"(.*)\"";

	regex1 = utext_openUTF8(regex1, argv[optind], -1, &status);
	//regex1 = utext_openUTF8(regex1, regex_validate_string, -1, &status);
	matchthis = utext_openUTF8(matchthis, argv[optind+1], -1, &status);

	RegexMatcher *matcher = new RegexMatcher(regex1, 0, status);
	if (U_FAILURE(status)) {
		// Handle any syntax errors in the regular expression here
		printf("Syntax error in regex?\n");
		icu::ErrorCode ec;
		ec.set(status);
		printf("Error was: %s\n",ec.errorName());
		utext_close(regex1);
		utext_close(matchthis);
		delete matcher;
		exit(exitcode);
	}

	if(!replace_mode) { // MATCH TEST

		//	UnicodeString    stringToTest = "Find the abc in this string";
		matcher->reset(matchthis);

		if (matcher->matches(status)) {
			// We found a match.
			printf("MATCH: string matches regex\n");
			//	   int startOfMatch = matcher->start(status);   // string index of start of match.

			if(matcher->groupCount() > 0) {
				UConverter *conv = ucnv_open("US-ASCII", &status);
				for(int x=0;x<=matcher->groupCount();x++) {
					//				UText *grp = NULL;
					UnicodeString US = matcher->group(x, status);
					if (U_FAILURE(status)) {
						icu::ErrorCode ec;
						ec.set(status);
						printf("Error was: %s\n",ec.errorName());
					} else {
						UChar *out = (UChar *) malloc(1000);
						char *outcs = (char *) malloc(1000);
						US.extract(out,1000,status);
						ucnv_fromUChars(conv,outcs,1000,out,u_strlen(out),&status);
						printf("Capture group %d: -->[%s]<--\n", x, outcs); // works as long as UTF8
						//					printf("Capture group %d: %s\n", x, grp); // works as long as UTF8
						if(out) free(out);
						if(outcs) free(outcs);
					}
				}
			}

			exitcode = 0;
		} else {
			printf("FAIL: no match\n");
			exitcode= 2;
		}

	} else { // REPLACER TEST
		UText *replacedtxt = NULL;
		UText *replacement = NULL;
		replacement = utext_openUTF8(replacement, argv[optind+2], -1, &status);
		matcher->reset(matchthis);
		printf("replacement: -->[%s]<--\n", argv[optind+2]);

		replacedtxt = matcher->replaceAll(replacement,replacedtxt,status);
		if (U_FAILURE(status)) {
			// Handle any syntax errors in the regular expression here
			printf("Syntax error in regex?\n");
			icu::ErrorCode ec;
			ec.set(status);
			printf("Error was: %s\n",ec.errorName());
			utext_close(regex1);
			utext_close(matchthis);
			utext_close(replacement);
			delete matcher;
			exit(exitcode);
		}

		if(replacedtxt) {
			// Replacement did something...
			printf("REPLACE: string replaced...\n");
			//	   int startOfMatch = matcher->start(status);   // string index of start of match.
			UChar buf[500];
			printf("new length: %ld\n", utext_nativeLength(replacedtxt));
			utext_extract(replacedtxt,0,500,buf,500,&status);

			if (U_FAILURE(status)) {
				// Handle any syntax errors in the regular expression here
				printf("Syntax error in extraction:\n");
				icu::ErrorCode ec;
				ec.set(status);
				printf("Error was: %s\n",ec.errorName());
				utext_close(regex1);
				utext_close(matchthis);
				utext_close(replacedtxt);
				utext_close(replacement);
				delete matcher;
				exit(exitcode);
			}

			// Yawn... and convert to ascii.  Can we make it any more complicated??
			UConverter *conv = ucnv_open("US-ASCII", &status);
			char *outcs = (char *) malloc(1000);
			ucnv_fromUChars(conv,outcs,1000,buf,u_strlen(buf),&status);

			// Also, use function u_strFromUTF8 / u_strToUTF8

			if (U_FAILURE(status)) {
				// Handle any syntax errors in the regular expression here
				printf("Syntax error in extraction:\n");
				icu::ErrorCode ec;
				ec.set(status);
				printf("Error was: %s\n",ec.errorName());
				utext_close(regex1);
				utext_close(matchthis);
				utext_close(replacedtxt);
				utext_close(replacement);
				free(outcs);
				delete matcher;
				exit(exitcode);
			}
			ucnv_close(conv);

			printf("Replaced result: -->[%s]<--\n", outcs); // works as long as UTF8
//			printf("Capture group %d: %s\n", x, grp); // works as long as UTF8
			if(outcs) free(outcs);
	utext_close(replacedtxt);
		} else {
			printf("Result: No replacement.\n");
		}

		utext_close(replacement);

	}
	utext_close(regex1);
	utext_close(matchthis);
	delete matcher;
	exit(exitcode);
}

Build

$ gcc regextest.cpp -licui18n -licuuc -licudata -o regextest