Data Structure in C++

Parsing Page Ranges

I have a question regarding segmentation fault.

I almost did this, but there is a segmentation fault

when only I type 1 to 10

 > 1,2,4,5 1,2,4,5 > 1 to 10 1,2,3,4,5,6,7,8,9,10 > 1,3 - 5,8 1, 3, 4, 5, 8 > 1 - 10 odd 1,3,5,7,9 

How can I fix segmentation fault ?

I think the problem is in exprss function, when I do if (numbs(*start) && opps(*(start+1)) && numbs(*(start+2)) && is_qualifier(*(start+3))) { Teacher said: you haven't checked to make sure that finish >= start+3. I.e., there might not be four elements in the input sequence, in which case you'll read off the end.

Then how can I fix this

My code is :

pset.cc

#include

#include

using std::string;

using std::cout;

struct pset {

virtual void evaluate() = 0;

};

struct pset_num : public pset {

pset_num (int value) {

v = value;

}

void evaluate() {

cout << v << ", ";

}

int v;

};

struct pset_range : public pset {

pset_range(int start, int end) {

s = start;

e = end;

}

void evaluate() {

for (int i = s; i <= e; i++) {

cout << i << ", ";

}

}

int s;

int e;

};

struct pset_to : public pset {

pset_to(string to, int start, int end) {

st = to;

s = start;

e = end;

}

void evaluate() {

if(st == "-" || st == "to") {

for (int i = s; i <= e; i++) {

cout << i << ", ";

}

}

}

string st;

int s;

int e;

};

struct pset_r_odd : public pset {

pset_r_odd(int start, int end) {

s = start;

e = end;

}

void evaluate() {

for (int i = s; i <= e; i++) {

if (i % 2 == 1)

cout << i << ", ";

}

}

int s;

int e;

};

struct pset_r_even : public pset {

pset_r_even(int start, int end) {

s = start;

e = end;

}

void evaluate() {

for (int i = s; i <= e; i++) {

if (i % 2 == 0)

cout << i << ", ";

}

}

int s;

int e;

};

main.cc

#include "pset.cc"

#include

#include

using std::cin;

using std::cout;

using std::vector;

using std::string;

using std::endl;

using iter = vector::iterator;

bool numbs(string s) {

return (s.at(0) >= '0' && s.at(0) <= '9');

}

bool opps(string s) {

return (s == "to" || s == "-");

}

bool is_qualifier(string s) {

return (s == "even" || s == "odd");

}

bool exprss(iter start, iter finish);

void parse_pset(iter start, iter finish);

vector lex(string s);

vector ranges;

int main() {

string input;

while (true) {

cout << "> ";

std::getline(cin, input);

vector tokens = lex(input);

bool valid = exprss(tokens.begin(), tokens.end() - 1);

if (valid) {

cout << "Valid" << std::endl;

parse_pset(tokens.begin(), tokens.end() - 1);

for (pset* exp : ranges) {

exp->evaluate();

}

ranges.clear();

cout << std::endl;

}

return 0;

}

vector lex(string s) {

const int SPACE = 0;

const int NUM = 1;

const int WORD = 2;

const int OP = 3;

int state = SPACE;

vector words;

string word;

for (char c : s) {

if (state == SPACE) {

if (c == ' ' || c == ',')

continue;

else if (c >= '0' && c <= '9')

state = NUM;

else if (c >= 'a' && c <'z')

state = WORD;

else if (c == '-')

state = OP;

word.push_back(c);

}

else {

int nstate = state;

if (c == ' ' || c == ',')

nstate = SPACE;

else if (c >= '0' && c <= '9')

nstate = NUM;

else if (c >= 'a' && c <= 'z')

nstate = WORD;

else if (c == '-')

nstate = OP;

if (nstate == SPACE) {

words.push_back(word);

word.clear();

state = SPACE;

continue;

}

if (nstate == state && state != OP)

word.push_back(c);

else if (nstate != state || state == OP) {

words.push_back(word);

word.clear();

word.push_back(c);

}

state = nstate;

}

}

if (!word.empty())

words.push_back(word);

return words;

}

void parse_pset(iter start, iter finish) {

if (start > finish)

return;

else if (start == finish) {

if(numbs(*start))

ranges.push_back(new pset_num{ stoi(*start) });

}

else {

if (numbs(*start) && opps(*(start+1)) &&

numbs(*(start+2)) && is_qualifier(*(start+3))) {

if (*(start+3) == "odd") {

ranges.push_back(new pset_r_odd{stoi(*start),

stoi(*(start+2))});

parse_pset(start+4, finish);

}

else if (*(start+3) == "even") {

ranges.push_back(new pset_r_even{stoi(*start),

stoi(*(start+2))});

parse_pset(start+4, finish);

}

}

else if (numbs(*start) && opps(*(start+1)) &&

numbs(*(start+2))) {

ranges.push_back(new pset_range{stoi(*start),stoi(*(start+2))});

parse_pset(start+3, finish);

}

else if (numbs(*start)){

ranges.push_back(new pset_num{ stoi(*start)});

parse_pset(start+1, finish);

}

}

return;

}

bool exprss(iter start, iter finish) {

if (start > finish)

return true;

else if (start == finish) {

if(numbs(*start))

return true;

else

return false;

}

else {

if (numbs(*start) && opps(*(start+1)) &&

numbs(*(start+2)) && is_qualifier(*(start+3))) {

return exprss(start+4, finish);

} else if (numbs(*start) && opps(*(start+1)) &&

numbs(*(start+2))) {

return exprss(start+3, finish);

} else if (numbs(*start)) {

return exprss(start+1, finish);

}

}

return false;

}