Dynamic recompiling

[Angeljruiz]

Hey everybody,
Well i created my first emulator. Currently, it only interprets. Ive learned first hand the obvious - its slow. So my solution is to make it dynamically recompile the code. Problem is i dont know where to start with dynamic recompiling. If anyone could give some extremely basic code examples of a link it would be great. Thanks :D

[Imadatobanisa]

What do you mean by "Dynamic recompiling" ?

[Jan Pasierb]

Dynamic compilation in C++? Good luck.

Seriously though try java's JIT mechanism.

[JLBorges]

A pure interpreted language would be the most appropriate to implement read-eval-print loops.
http://docs.python.org/2/library/code.html

And then hook C++ up with a glue library - for instance, Boost.Python.
http://www.boost.org/doc/libs/1_52_0/libs/python/doc/index.html



> Problem is i dont know where to start with dynamic recompiling.
> If anyone could give some extremely basic code examples of a link it would be great.

Here is a toy example of dynamic recompiling with C++:

int f( int x, int y )
{
    return
        x+y-45;
}

#include <iostream>
#include <string>
#include <vector>
#include <fstream>
#include <cstdlib>

std::vector<std::string> read_lines( const char* path2file )
{
    std::vector<std::string> vec ;
    std::ifstream file(path2file) ;
    std::string line ;
    while( std::getline(file,line) ) vec.push_back(line) ;
    return vec ;
}

void write_lines( std::vector<std::string>& lines, const char* path2file )
{
    // make a backup copy of the file first
    std::ofstream file(path2file) ;
    for( const auto& s : lines ) file << s << '\n' ;
}

std::string get_fn_expr()
{
    std::string expr ;
    std::cout << "enter expression for f(x,y):\n\tfor example x*x*x + y*y - 23 ? " ;
    std::getline( std::cin, expr ) ;
    // validate expr
    return expr.empty() ? get_fn_expr() : expr ;
}

void do_recompile_and_run()
{
    std::cout << "recompiling. please wait..." ;

    // adjust command(s) appropriately for the implementation
    std::string recompile_cmd = "/bin/g++ -Wall -std=c++11 --pedantic -Wall -Wextra -Werror " ;
    recompile_cmd += __FILE__ ;
    recompile_cmd += "&& ./a.out run" ;

    std::system( recompile_cmd.c_str() ) ;
}

void modify_function_and_recompile()
{
    std::vector<std::string> code = read_lines(__FILE__) ;
    enum { LINE_TO_MODIFY = 3 } ;
    code[LINE_TO_MODIFY] = "        " + get_fn_expr() + ';' ;
    write_lines( code, __FILE__ ) ;
    do_recompile_and_run() ;
}

void run()
{
    std::cout << " done. running the program now.\n" ;
    int x, y ;
    std::cout << "x? " && std::cin >> x ;
    std::cout << "y? " && std::cin >> y ;
    std::cout << "f(x,y) evaluates to " << f(x,y) << '\n' ;
}

int main( int argc, char*[] )
{
    if( argc == 1 ) modify_function_and_recompile() ;
    else run() ;
}