trim函数

找来找去, C++库里竟然没trim函数, 那自己写咯

static std::string ltrim(const std::string & str) {
	std::string::iterator iter;
	std::string ss = str;
	for (iter = ss.begin(); iter != ss.end(); iter++) {
		if (!isspace(*iter))
			break;
	}
	ss.erase(ss.begin(), iter);
	return ss;
}

static std::string rtrim(const std::string & str) {
	std::string::iterator iter;
	std::string ss = str;
	for (iter = ss.end(); iter != ss.begin(); iter--) {
		if (!isspace(*iter - 1))
			break;
	}
	ss.erase(iter, ss.end());
	return ss;
}

static std::string trim(const std::string & str) {
	return ltrim(rtrim(str));
}