Simple example of a query parser in C++.

parse_query.cpp

#include <iostream>
#include <sstream>
#include <string>

using namespace::std;

void parseTerms(string query, string components[][3]);
void parseToken(string token, string parsed[]);

int main() {
	string query = "makemodel=acura nsx year=1997 price<=1500";
	string terms[3][3];
	parseTerms(query, terms);
	for (int i = 0; i < 3; ++i) {
		cout << "i=" << i << " [0]=\"" << terms[i][0] << "\" [1]=\"" << terms[i][1] << "\" [2]=\"" << terms[i][2] << "\"" << endl;
	}
	return 0;
}

void parseTerms(string query, string terms[][3]) {
	stringstream ss(query);
	string token;
	int i = 0;
	while (ss >> token) {
		if (token.length() > 0) {
			// cout << "i=" << i << " token=\"" << token << "\"" << endl;
			parseToken(token, terms[i]);
			// cout << "i=" << i << " [0]=\"" << terms[i][0] << "\" [1]=\"" << terms[i][1] << "\" [2]=\"" << terms[i][2] << "\"" << endl;
			if (terms[i][1].length() == 0) {
				if (i > 0) {
					terms[i-1][2] += " " + terms[i][0];
				}
			} else {
				++i;
			}
		}
	}
}

void parseToken(string token, string parsed[]) {
	unsigned short stage = 0;
	for (int i = 0; i < token.length(); ++i) {
		switch(stage) {
			case 0:
				if (token[i] < 'A' || token[i] > 'z') {
					++stage;
				}
				break;
			case 1:
				if (token[i] != '<' && token[i] != '>' && token[i] != '=' && token[i] != '!') {
					++stage;
				}
				break;
		}
		parsed[stage] += token[i];
	}
}

parse_query_min_includes.cpp

#include <iostream>

using namespace::std;

void parseTerms(string query, string components[][3]);
void parseToken(string token, string parsed[]);

int main() {
	string query = "makemodel=acura nsx year=1997 price<=1500";
	string terms[3][3];
	parseTerms(query, terms);
	for (int i = 0; i < 3; ++i) {
		cout << "i=" << i << " [0]=\"" << terms[i][0] << "\" [1]=\"" << terms[i][1] << "\" [2]=\"" << terms[i][2] << "\"" << endl;
	}
	return 0;
}

void parseTerms(string query, string terms[][3]) {
	string token;
	int i = 0;
	for (int j = 0; j < query.length(); ++j) {
		if (query[j] != ' ') {
			token += query[j];
		}
		if (token.length() > 0 && (j == query.length() - 1 || query[j+1] == ' ')) {
			// cout << "i=" << i << " token=\"" << token << "\"" << endl;
			parseToken(token, terms[i]);
			// cout << "i=" << i << " [0]=\"" << terms[i][0] << "\" [1]=\"" << terms[i][1] << "\" [2]=\"" << terms[i][2] << "\"" << endl;
			if (terms[i][1].length() == 0) {
				if (i > 0) {
					terms[i-1][2] += " " + terms[i][0];
				}
			} else {
				++i;
			}
			token = "";
		}
	}
}

void parseToken(string token, string parsed[]) {
	unsigned short stage = 0;
	for (int i = 0; i < token.length(); ++i) {
		switch(stage) {
			case 0:
				if (token[i] < 'A' || token[i] > 'z') {
					++stage;
				}
				break;
			case 1:
				if (token[i] != '<' && token[i] != '>' && token[i] != '=' && token[i] != '!') {
					++stage;
				}
				break;
		}
		parsed[stage] += token[i];
	}
}