bf.cc

/* bf.cc */

#include <iostream>
#include <fstream>
#include <vector>

typedef char heap_type;
int main(int argc, char** argv) {
	std::ifstream in;

	if(argc <= 1) {
		std::cout << "Usage: bf [file]" << std::endl;
		return 1;
	}

	/* Open the file and get its size. */
	in.open(argv[1]);
	in.seekg(0, in.end);
	const int filesize = in.tellg();
	in.seekg(0, in.beg);

	/* Allocate and populate the source code buffer. */
	char* code = new char[filesize];

	in.read(code, filesize);

	in.close();


	/* It is customary to have at least thirty thousand places in the heap. */
	const int heapsize = 30000;
	heap_type* heap = new heap_type[heapsize];

	for(int i = 0; i < heapsize; i++) {
		heap[i] = 0;
	}


	std::vector<int> stack;

	heap_type* ptr = heap;
	int index = 0;

	while(index < filesize) {
		char c = code[index];
		index++;

		switch(c) {
		case '[':
			if(*ptr) {
				/* Note where this loop began. If a corresponding closing brace is encountered then jump back here. */
				stack.push_back(index - 1);
			} else {
				/* Exit the loop by reading enough braces so that the current brace is cancelled out. */
				int depth = 1;

				while(index < filesize && depth > 0) {
					if(code[index] == '[') {
						depth++;
					} else if(code[index] == ']') {
						depth--;
					}

					index++;
				}
			}

			break;

		case ']':
			if(stack.size() > 0) {
				/* Jump back to the beginning of the loop. */
				index = stack[stack.size() - 1];
				stack.pop_back();
			} else {
				/* This closing brace has no corresponding opening brace. That makes this program invalid. */
				std::cerr << "Mismatched brackets" << std::endl;
				delete [] heap;
				delete [] code;

				return 1;
			}

			break;

		case '<':
			/* Move the pointer back. */
			--ptr;
			break;

		case '>':
			/* Move the pointer forward. */
			++ptr;
			break;

		case '-':
			/* Decrease the value. */
			--*ptr;
			break;

		case '+':
			/* Increase the value. */
			++*ptr;
			break;

		case '.':
			/* Output the value. */
			std::cout << *ptr;
			break;

		case ',':
			/* Input the value. */
			std::cin >> *ptr;
			break;

		default:
			/* Ignore every other character. */
			break;
		}
	}

	delete [] heap;
	delete [] code;

	return 0;
}