Brainfuck interpreter in C++

bf.cc

#include <iostream>
#include <cstring>
#include <fstream>

#define MAX_LINE 2048
#define DATA_ALLOC 30000

using namespace std;

void fuck(char *start, char *end) {
  static char data[DATA_ALLOC];
  static char *ptr = data;
  char *bstart, *bend;
  size_t depth = 0;
  while (start < end) {
    char ch = *start;
    if (depth) {
      if (ch == '[') {
        depth++;
      } else if (ch == ']') {
        depth--;
      }
      if (depth == 0) {
        while (*ptr) {
          fuck(bstart, bend);
        }
      } else {
        bend++;
      }
    } else {
      switch (ch) {
        case '[':
          depth++;
          bstart = start + 1;
          bend = start + 2;
          break;
        case '+':
          ++*ptr;
          break;
        case '-':
          --*ptr;
          break;
        case '>':
          ++ptr;
          break;
        case '<':
          --ptr;
          break;
        case '.':
          cout << *ptr;
          break;
        case ',':
          *ptr = getchar();
          break;
      }
    }
    start++;
  }
}

void fuck(string input) {
  char *cstr = (char*) input.c_str();
  fuck(cstr, cstr + input.size());
}

string read_file(string name) {
  fstream stream(name, ios_base::in);
  string result, line;
  string valid_chars = "[].,-+<>";
  while (getline(stream, line)) {
    for (const auto& c: line) {
      if (valid_chars.find(c) != -1) {
        result.append(sizeof(char), c);
      }
    }
  }
  stream.close();
  return result;
}

int main(int argc, char **argv) {
  fuck(read_file(argv[1]));
  return 0;
}