regex.hとloopのパフォーマンス比較

Using regex.h

regexTime.cc

regex_t preg;
size_t nmatch = 5;
regmatch_t pmatch[nmatch];
int ret = regcomp(&preg, "[[:digit:]]+.[[:digit:]].[[:digit:]]",
				  REG_EXTENDED | REG_NEWLINE);
if( ret ){
	cout << "regex compile failed" << endl;
}
cout << "String: " << str << endl;
if( regexec(&preg, str, nmatch, pmatch, 0) != 0 ){
	cout << "no match" << endl;
}
else{
	for( int i = 0 ; i < nmatch ; i++ ){
		for( int j = pmatch[i].rm_so ; j < pmatch[i].rm_eo ; j++ ){
			cout << str[j];
		}
	}
	cout << endl;
}

Using only for loop

loopTime.cc

int i,j;
int c, l = strlen(str);
for (i = j = 0; i < l; i++) {
	c = OPENSSL_VERSION_TEXT[i];
	if ('0' <= c && c <= '9') {
		for (j = i + 1; j < l; j++) {
			c = str[j];
			if (c == ' '){
				break;
			}
		}
		break;
	}
}
for( int k = i ; k < j - i + 2; k++ ){
	putchar(str[k]);
}
return 0;

$ time ./regexTime
real	0m0.005s
user	0m0.002s
sys	0m0.002s

$ time ./loopTime
real	0m0.005s
user	0m0.002s
sys	0m0.002s

No difference