A Simple Brinfuck to C Compiler!

This time we're going to look at a simple brainfuck compiler to C code, based on this: http://www.muppetlabs.com/~breadbox/bf/
Incase you didn't know, brainfuck is a really cool little language which has only got 8 instructions, the code looks like this:

++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>.

This tutorial is based heavily on the code from the previous one, so make sure to have read that first!

// Most of this is heavily based on the previous tutorial
// So we've just copied the file and changed a couple of things
// This time, we filter like before but print out different text
// instead.

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

int heapsize;
char * filter_string;
FILE * input_file, * output_file;

void display_usage(char * name) {
  printf("usage: %s [-i input filename] [-o output filename] [-h heapsize, default 512]\n", name);
}

int process_args(int argc, char ** argv) {
  int ch;
  
  // Deal with the command line arguments here
  // return 1 on success, 0 on failure
  // (failure meaning malformed parameters or anything)
  
  heapsize = 512;
  input_file = stdin;
  output_file = stdout;
  
  while((ch = getopt(argc, argv, "i:o:h:")) != -1) { // look at all the args + -heap
    // getopt returns -1 once it's finished
    if(ch == '?') return 0;
    
    switch(ch) {
    case 'i':
      input_file = fopen(optarg, "r");
      if(!input_file) {
        printf("Could not open input file \"%s\"\n", optarg);
        return 0;
      }
      break;
    case 'o':
      output_file = fopen(optarg, "w");
      if(!output_file) {
        printf("Could not open output file \"%s\"\n", optarg);
        return 0;
      }
      break;
    case 'h':
      heapsize = atoi(optarg);
      break;
    }
  }
  
  return 1;
}

// Heres the first version:
int main(int argc, char ** argv) {
  int ch;
  
  if(!process_args(argc, argv)) {
    display_usage(argv[0]); // ammendment, argv[0] is the program name
                           // we shall display this in usage
    return EXIT_FAILURE;
  }
  
  filter_string = ".,+-<>[]";
  fputs("#include <stdio.h>\n", output_file);
  fputs("#include <stdlib.h>\n", output_file);
  fprintf(output_file, "static int heap[%d];\n", heapsize);
  fprintf(output_file, "int main(void) {int * p = heap+%d;", heapsize/2);
  while((ch = fgetc(input_file)) != EOF)
    switch(ch) {
    case '>':  break;
    case '<': fputs("--p;", output_file); break;
    case '+': fputs("++*p;", output_file); break;
    case '-': fputs("--*p;", output_file); break;
    case '.': fputs("putchar(*p);", output_file); break;
    case ',': fputs("*p = getchar();", output_file); break;
    case '[': fputs("while (*p) {", output_file); break;
    case ']': fputs("}", output_file); break;
    }
  fputs("return EXIT_SUCCESS;}\n", output_file);
  fflush(output_file);
  fclose(output_file);
  
  return EXIT_SUCCESS;
}

// it seesm to work well but there's some improvements possible.
// Example outout: int main(void) {int * p = heap+256;putchar(*p);++p;++*p;++*p;++*p;++*p;++*p;++*p;++*p;++p;++*p;++*p;++*p;++*p;++*p;++*p;++*p;++*p;++*p;++*p;while (*p) {--p;++*p;++*p;++*p;++*p;++*p;++p;--*p;}++*p;++*p;++*p;++*p;++*p;++*p;++*p;++p;++*p;++*p;++*p;++*p;++*p;++*p;++*p;++*p;++*p;++*p;while (*p) {--p;++....
// all these ++p could be turned into a single p+=50;
// similarly with -- ++* and --*
// that'll be next!