A simple brainfuck interpreter in C (update)

bf.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

// initialize the tape with 30,000 zeroes
unsigned char tape[30000] = {0};

// set the pointer to point at the left-most cell of the tape
unsigned char* ptr = tape;


void interpret(char* input) {
  char current_char;
  size_t i;
  size_t loop;

  for (i = 0; input[i] != 0; i++) {
    current_char = input[i];
    if (current_char == '>') {
      ++ptr;
    } else if (current_char == '<') {
      --ptr;
    } else if (current_char == '+') {
      ++*ptr;
    } else if (current_char == '-') {
      --*ptr;
    } else if (current_char == '.' ) {
      putchar(*ptr);
    } else if (current_char == ',') {
      *ptr = getchar();
    } else if (current_char == '[') {
      continue;
    } else if (current_char == ']' && *ptr) {
      loop = 1;
      while (loop > 0) {
        current_char = input[--i];
        if (current_char == '[') {
          loop--;
        } else if (current_char == ']') {
          loop++;
        }
      }
    }
  }
}


int main(int argc, char *argv[]) {

  if (argc != 2)
  {
    printf("Usage: %s file.bf\n", argv[0]);
    exit(2);
  }

  FILE *file = fopen(argv[1], "r");
  if (file == NULL)
  {
    printf("Error: fopen failed\n");
    exit(1);
  }

  fseek(file, 0L, SEEK_END);
  long file_len = ftell(file);
  rewind(file);

  char *file_buf = malloc(file_len * sizeof(char) + 1);
  file_buf[file_len] = '\0';

  fread(file_buf, file_len, sizeof(char), file);
  fclose(file);

  interpret(file_buf);  // outputs input

  free(file_buf);
  return 0;
}

Original authors is @maxcountryman, see his version here

Simple update to read bf code from a file

As has been mentioned, '[' must jump back to the ']' if memory cell == 0, for a compliant implementation.