Jim Langston wrote:
"gr" <gr********@gmail.comwrote in message
news:11*********************@m73g2000cwd.googlegro ups.com...
hi.. I must implement an interpreter in C programming language that
will get the source code of a program in text file format and execute
it.
but i don't know C language enough to write this interpreter. so I need
this interpreter code that is written with C language.(or it can be
C++) I searched this codes in google and some websites, but codes which
I found are useless..
if you can help me, you gladden me.
please help me.. :(
*************************
a part from my homework;
Your interpreter program will accept and execute statements below:
· int variable_name
· cin>variable_name
· cout<< variable_name
· variable_name = infix arithmetic expression (variable names, +, -,
*, /, and parentheses (..)).
· for loop
· if else statement
(your interpreter does not need to recognize and execute nested for and
if/else statements .
It should give error messages. Possible syntactic errors relating
source code input are:
· Undefined variable <variable_name>
· Paranthesis mismatch
· Curly brackets mismatch
For the arithmetic expression evaluation you are free to use directly
an existing evaluator program source code like polish notation within
your interpreter.
---------
Very difficult assignment. I will say, though, that if you can get it done
you'll learn a lot.
A book I picked up years ago, The ART of C++, has the code for a mini C++
interpreter. The book itself actually isn't that good, but it does have
that.
Horrible assignment. Can you get to a library? If so, try "Constructing Language
Processors for Little Languages" by Randy M. Kaplan. Another you might be able to get
a hold of is "Compiler Design in C" by Allen I Holub, though this is probably just a
bit too advanced but still readable. In both of these the code samples are written in
C. Another you might try (in C++ this time - though not in the modern idiomatic
style) is "Writing Compilers and Interpreters" by Ronald Mak.
To start with you will need a stack. This will help you with parenthesis matching and
expression evaluation (among other things).
To illustrate, a simple function to check whether or not an arbitrary string has
balanced parentheses can be easily constructed as follows (warning: this is not
idiomatic C++, does not do any argument checking and assumes a "C" locale):
bool hasMatchedParentheses (std:string const& in)
{
std::string::size_type const insize(in.size());
std::string::size_type nparens(0);
for (std::string::size_type i(0); i != insize; ++i)
{
switch (in[i])
{
case '(':
++nparens;
break;
case ')':
--nparens;
break;
default:
break;
}
}
return nparens != 0;
}
This function uses an unsigned integral type as a "stack" to check for matched
parentheses. A non-zero value indicates an unbalanced set. You might ask what happens
if the number of ')' characters is greater than the number of '(' characters or if a
')' appears before '(' in the string? Well nparens will wrap round to a large
positive value since the standard guarantees this for unsigned integral types. In
this case, nparens is still non-zero so the test in the return statement will still
catch the error. One case it does _not_ handle is a string containing no parentheses
at all.
This function of course needs reworking to indicate the position where the error
occurred and what kind of error it was but it is sufficient to illustrate the kind of
thing you will need to do.
Hope this helps,
Jim.
