brainfuck.cpp

#include <cstdio>
struct Node {
  unsigned char data;
  Node *pre, *next;
  Node(unsigned char d = 0, Node *p = nullptr, Node *n = nullptr) {
    data = d;
    pre = p;
    next = n;
  }
} * memory, *source;
Node *left(Node **nd) {
  if ((*nd)->pre != nullptr) (*nd) = (*nd)->pre;
  return *nd;
}
Node *right(Node **nd) {
  if ((*nd)->next == nullptr) {
    Node *t = new Node;
    (*nd)->next = t;
    t->pre = *nd;
  }
  (*nd) = (*nd)->next;
  return *nd;
}
int init_code(FILE *code) {
  char c;
  source = new Node;
  while (true) {
    bool flag = 1;
    do {
      const char *cmd = "+-<>,.[]";
      c = fgetc(code);
      if (c == EOF) break;
      for (int idx = 0; idx < 8; idx++)
        if (c == cmd[idx]) {
          flag = 0;
          break;
        }
    } while (flag);
    if (c == EOF) break;
    right(&source);
    source->data = c;
  }
  while (source->data)
    left(&source);
  return 0;
}
int run() {
  bool err = 0;
  memory = new Node;
  while (1) {
    if (source->next == nullptr) break;
    right(&source);
    char c = source->data;
    switch (c) {
    case '+':
      memory->data++;
      break;
    case '-':
      memory->data--;
      break;
    case '<':
      if (memory->pre == nullptr) {
        err = 1;
        break;
      }
      left(&memory);
      break;
    case '>':
      right(&memory);
      break;
    case ',':
      memory->data = getchar();
      break;
    case '.':
      putchar(memory->data);
      break;
    case '[':
      if (memory->data == 0) {
        int le = 1;
        while (source->next != nullptr) {
          right(&source);
          if (source->data == '[') le++;
          if (source->data == ']') le--;
          if (!le) break;
        }
        if (le) err = 1;
      }
      break;
    case ']':
      if (memory->data) {
        int ri = 1;
        while (source->pre != nullptr) {
          left(&source);
          if (source->data == '[') ri--;
          if (source->data == ']') ri++;
          if (!ri) break;
        }
        if (ri) err = 1;
      }
      break;
    default:
      break;
    }
    if (err) break;
  }
  if (err) {
    puts("Runtime Error!");
    return -1;
  }
  return 0;
}
int main(const int argc, const char **argv) {
  FILE *code;
  if (argc != 2) return -1;
  code = fopen(argv[1], "r");
  if (code == nullptr) return -1;
  return init_code(code) + run();
}