bf.cpp

/*
+ : Increments the value at the current cell by one.
- : Decrements the value at the current cell by one.
> : Moves the data pointer to the next cell (cell on the right).
< : Moves the data pointer to the previous cell (cell on the left).
. : Prints the ASCII value at the current cell (i.e. 65 = 'A').
, : Reads a single input character into the current cell.
[ : If the value at the current cell is zero, skips to the corresponding ] .
    Otherwise, move to the next instruction.
] : If the value at the current cell is zero, move to the next instruction.
    Otherwise, move backwards in the instructions to the corresponding [ .
*/

#include <iostream>
#include <fstream>
#include <streambuf>
#include <algorithm>
#include <string>
#include <vector>

class BrainfuckTape {
public:
    BrainfuckTape(): tape{0}, tape_ptr(tape.begin()) {
    }

    ~BrainfuckTape() {
     }

    void inc() {
        (*tape_ptr)++;
    }

    void dec() {
        (*tape_ptr)--;
    }

    void next() {
        tape_ptr++;
    }

    void prev() {
        tape_ptr--;
    }

    void out() {
        std::cout << char(*tape_ptr);
    }

    void get() {
    }

    int value() {
        return *tape_ptr;
    }

private:
    std::vector<int> tape;
    std::vector<int>::iterator tape_ptr;
};

void error(const std::string &msg) {
    std::cerr << "error: " << msg << std::endl;
    return;
}

void compile(std::string code) {
    BrainfuckTape tape;
    std::string::iterator loop_begin;

    for(std::string::iterator iter = code.begin(), end = code.end(); iter != end; iter++) {
        if(*iter == '+') {
            tape.inc();
        } else if(*iter == '-') {
            tape.dec();
        } else if(*iter == '>') {
            tape.next();
        } else if(*iter == '<') {
            tape.prev();
        } else if(*iter == '.') {
            tape.out();
        } else if(*iter == ',') {
            tape.get();
        } else if(*iter == '[') {
            if(tape.value() == 0) {
                iter = std::find(iter, code.end(), ']');
            } else {
                loop_begin = iter;
            }
        } else if(*iter == ']') {
            if(tape.value() == 0) {
                iter++;
            } else {
                iter = loop_begin;
            }
        }
    }

    std::cout << std::endl;
}

int main(int argc, char *argv[]) {
    int status = 0;

    if(argc != 2) {
        error("improper usage.\nusage: " + std::string(argv[0]) + " FILE");
        status = 1;
    } else {
        std::ifstream handle(argv[1]);

        if(not handle) {
            error("could not open file.");
            status = 1;
        } else {
            std::string code((std::istreambuf_iterator<char>(handle)), std::istreambuf_iterator<char>());
            compile(code);
        }
    }

    return status;
}