Brainfuck to C compiler.

bf.c

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

void die(const char* msg) {
  puts(msg);
  exit(1);
}

void cp(FILE* a, FILE* b) {
  int c;
  while((c = fgetc(a)) != EOF)
    fputc(c, b);
}

void compile(FILE* in, FILE* out) {
  int c;
  int nest = 0;

  fputs("void run(void) {", out);

  while((c = fgetc(in)) != EOF) {
    switch(c) {
    case '>': fputs("i = (i + 1) % SIZE;", out); break;
    case '<': fputs("i = (i - 1) % SIZE;", out); break;
    case '+': fputs("++a[i];", out);             break;
    case '-': fputs("--a[i];", out);             break;
    case '.': fputs("putchar(a[i]);", out);      break;
    case ',': fputs("a[i] = getchar();", out);   break;
    case '[':
      fputs("while(a[i]) {", out);
      ++nest;
      break;
    case ']':
      fputs("}", out);
      if(--nest < 0) die("unbalanced square brackets");
      break;
    default: continue;
    }

    fputc('\n', out);
  }

  if(nest != 0) die("unbalanced square brackets");

  fputs("}", out);
}

int main(int argc, char** argv) {
  if(argc != 2)
    die("provide exactly one argument (the file to compile)");

  FILE* in = fopen(argv[1], "r");
  if(!in) die("cannot open file");

  FILE* out = fopen("out.c", "w");
  if(!out) die("cannot open file: out.c");

  FILE* template = fopen("template.c", "r");
  if(!template) die("cannot open file: template.c");

  cp(template, out);

  fclose(template);

  compile(in, out);

  fclose(in);
  fclose(out);
  return 0;
}

run

#!/bin/sh
# ./run <(echo ',+[-.,+]')

gcc -pedantic -Wall -Wextra -Werror bf.c || exit

./a.out $1 || exit

gcc -pedantic -Wall -Wextra -Werror -o out out.c || exit
./out

rm -f a.out out out.c

template.c

#include <stddef.h>
#include <stdio.h>

#define SIZE 0x10000

char a[SIZE];
size_t i = 0;

void run(void);

int main(void) {
  run();
  return 0;
}