email.cc

#include <vector>
#include <iostream>
#include <algorithm>
#include <locale>
#include <sstream>

using namespace std;

int catchEmailBegin(string str, int place)
{
  int res = -1;
  for (int i = place - 1; i > 0; i--)
  {
    if (!(isalpha(str[i]) || isdigit(str[i])))
    {
      res = i + 1;
      break;
    }
  }
  return res;
}

int catchEmailEnd(string str, int place)
{
  int res = -1;
  int domain_length = 0;
  bool find_dot = false;
  for (size_t i = place + 1; i < str.length(); i++)
  {
    if (str[i] == '.')
    {
      find_dot = true;
      domain_length = -1;
    }
    if (!(isalpha(str[i]) || isdigit(str[i]) || str[i] == '.'))
    {
      // cout << "domain_length: " << domain_length << endl;
      if (domain_length >= 2 && domain_length <= 4)
      {
        res = i;
      }
      break;
    }
    else
    {
      if (find_dot)
      {
        domain_length++;
      }
    }
  }
  if (res == -1 && find_dot && domain_length >= 2 && domain_length <= 4)
  {
    res = str.length();
  }
  return res;
}

vector<string> extractEmail(string str)
{
  std::string delim = "@";

  int start = 0;
  vector<string> res;

  int begin = 0, end = 0, place = 0;
  for (;;)
  {
    place = str.find(delim, start);
    if (place == string::npos)
    {
      break;
    }
    begin = catchEmailBegin(str, place);
    if (begin == -1)
    {
      goto next;
    }
    end = catchEmailEnd(str, place);
    if (end == -1)
    {
      goto next;
    }
  next:
    // cout << begin << " " << end << endl;
    if (begin != -1 && end != -1)
    {
      // cout << begin << " " << end << str.substr(begin, end - begin) << endl;
      res.push_back(str.substr(begin, end - begin));
    }
    start = place + delim.length();
  }
  return res;
}

template <typename T>
string array_show(vector<T> vec)
{
  stringstream ss;
  ss << "[";
  for (auto it = vec.begin(); it != vec.end(); ++it)
  {
    if (it != vec.begin())
    {
      ss << ", " << *it;
    }
    else
    {
      ss << *it;
    }
  }
  ss << "]";
  return ss.str();
}

int main(int argc, char const *argv[])
{
  string input = "hello abc123@qq.com.com a@b.com";
  cout << "res: " << array_show(extractEmail(input)) << endl;

  return EXIT_SUCCESS;
}

Makefile

CCFiles         := $(wildcard *.cc)

.PHONY: cc
cc: $(CCFiles)

.PHONY: $(CCFiles)
$(CCFiles):
	@echo Running `echo $@ | cut -d. -f1`:
	@echo
	@$(CXX) -std=c++17 -lm -Os -g3 -fsanitize=address,signed-integer-overflow \
	-o `echo $@ | cut -d. -f1`.test $@
	@./`echo $@ | cut -d. -f1`.test
	@$(RM) -rf `echo $@ | cut -d. -f1`.test *.dSYM
	@echo