ani2ico, like the file converter with c++

ani2ico.cpp

#include <cstring>
#include <fstream>
#include <iostream>
#include <string>
#include <vector>

using namespace std;

void parse(string const &name);
bool is_icon(char const *buffer);

int main(int argc, char **argv) {
  if (argc != 2) {
    cerr << "Please give an .ani filename as an argument!\n";
    return 0;
  }

  parse({argv[1]});
  return 0;
}

void parse(string const &name) {
  if (name.find(".ani") == string::npos) {
    cerr << "Please give an .ani filename as an argument!\n";
    return;
  }

  ifstream file(name, ios::binary);
  if (!file.is_open()) {
    cerr << "Unable to open file " << name << "\n";
    return;
  }

  file.seekg(0, fstream::end);
  size_t fileLen = file.tellg();
  file.seekg(0, fstream::beg);

  vector<char> buffer(fileLen + 1);

  file.read(buffer.data(), fileLen);
  file.close();

  string new_ico_name;

  int ico_counter = 1;

  for (size_t i = 0; i <= fileLen; i++) {
    if (ico_counter >= 9999) {
      return;
    }

    if ((i + 4 <= fileLen) && find_icon(&buffer[i])) {
      new_ico_name = name;
      new_ico_name += ico_counter;
      new_ico_name += ".ico";
      ico_counter++;

      ofstream ico_image(new_ico_name, ios::binary);

      if (!ico_image.is_open()) {
        cerr << "Unable to save file " << new_ico_name << "\n";
        break;
      }

      size_t j = 8;
      while (i + j + 4 <= fileLen) {
        if (is_icon(&buffer[i + j + 1]))
          break;

        if (j == 10) {
          ico_image << static_cast<char>(0x01);
        } else {
          ico_image << buffer[i + j];
        }
        j++;
      }
      if (i + j <= fileLen)
        ico_image << buffer[i + j];
      if (fileLen - i - j <= 3) {
        ico_image << buffer[i + j + 1];
        ico_image << buffer[i + j + 2];
      }
      i += j;
    }
  }
}

bool is_icon(char const *buffer) {
  return std::strncmp(buffer, "icon", 4);
}