chsh.cpp

一个类c++语言解释器

#include <iostream>
#include <fstream>
#include <new>
#include <stack>
#include <vector>
#include <cstring>
#include <cstdlib>
#include <cctype>
#include "chsh.h"

using namespace std;

char *prog;  // current execution point in source code
char *p_buf; // points to start of program buffer

// This structure encapsulates the info
// associated with variables.
struct var_type {
  char var_name[MAX_ID_LEN+1]; // name
  token_ireps v_type; // data type
  int value; // value
};

// This vector holds info for global variables.
vector<var_type> global_vars;

// This vector holds info for local variables
// and parameters.
vector<var_type> local_var_stack;

// This structure encapsulates function info.
struct func_type {
  char func_name[MAX_ID_LEN+1]; // name
  token_ireps ret_type; // return type
  char *loc; // location of entry point in program
};

// This vector holds info about functions.
vector<func_type> func_table;

// Stack for managing function scope.
stack<int> func_call_stack;

// Stack for managing nested scopes.
stack<int> nest_scope_stack;

char token[MAX_T_LEN+1]; // current token
tok_types token_type; // token type
token_ireps tok; // internal representation

int ret_value; // function return value

bool breakfound = false; // true if break encountered

int main(int argc, char *argv[])
{
  if(argc != 2) {
    cout << "Usage: minicpp <filename>\n";
    return 1;
  }

  // Allocate memory for the program.
  try {
    p_buf = new char[PROG_SIZE];
  } catch (bad_alloc exc) {
    cout << "Could Not Allocate Program Buffer\n";
    return 1;
  }

  // Load the program to execute.
  if(!load_program(p_buf, argv[1])) return 1;

  // Set program pointer to start of program buffer.
  prog = p_buf;

  try {
    // Find the location of all functions
    // and global variables in the program.
    prescan();

    // Next, set up the call to main().

    // Find program starting point.
    prog = find_func("main");

    // Check for incorrect or missing main() function.
    if(!prog) {
      cout << "main() Not Found\n";
      return 1;
    }

    // Back up to opening (.
    prog--;

    // Set the first token to main
    strcpy(token, "main");

    // Call main() to start interpreting.
    call();
  }
  catch(InterpExc exc) {
    sntx_err(exc.get_err());
    return 1;
  }
  catch(bad_alloc exc) {
    cout << "Out Of Memory\n";
    return 1;
  }

  return ret_value;
}

// Load a program.
bool load_program(char *p, char *fname)
{
  int i=0;

  ifstream in(fname, ios::in | ios::binary);
  if(!in) {
    cout << "Cannot Open file.\n";
    return false;
  }

  do {
    *p = in.get();
    p++; i++;
  } while(!in.eof() && i < PROG_SIZE);

  if(i == PROG_SIZE) {
    cout << "Program Too Big\n";
    return false;
  }

  // Null terminate the program. Skip any EOF
  // mark if present in the file.
  if(*(p-2) == 0x1a) *(p-2) = '\0';
  else *(p-1) = '\0';

  in.close();

  return true;
}

// Find the location of all functions in the program
// and store global variables.
void prescan()
{
  char *p, *tp;
  char temp[MAX_ID_LEN+1];
  token_ireps datatype;
  func_type ft;

  // When brace is 0, the current source position
  // is outside of any function.
  int brace = 0;

  p = prog;

  do {
    // Bypass code inside functions
    while(brace) {
      get_token();
      if(tok == END) throw InterpExc(UNBAL_BRACES);
      if(*token == '{') brace++;
      if(*token == '}') brace--;
    }

    tp = prog; // save current position
    get_token();

    // See if global var type or function return type.
    if(tok==CHAR || tok==INT) {
      datatype = tok; // save data type
      get_token();

      if(token_type == IDENTIFIER) {
        strcpy(temp, token);
        get_token();

        if(*token != '(') { // must be global var
          prog = tp; // return to start of declaration
          decl_global();
        }
        else if(*token == '(') { // must be a function

          // See if function already defined.
          for(unsigned i=0; i < func_table.size(); i++)
            if(!strcmp(func_table[i].func_name, temp))
              throw InterpExc(DUP_FUNC);

          ft.loc = prog;
          ft.ret_type = datatype;
          strcpy(ft.func_name, temp);
          func_table.push_back(ft);

          do {
            get_token();
          } while(*token != ')');
          // Next token will now be opening curly
          // brace of function.
        }
        else putback();
      }
    }
    else {
      if(*token == '{') brace++;
      if(*token == '}') brace--;
    }
  } while(tok != END);
  if(brace) throw InterpExc(UNBAL_BRACES);
  prog = p;
}

// Interpret a single statement or block of code. When
// interp() returns from its initial call, the final
// brace (or a return) in main() has been encountered.
void interp()
{
  int value;
  int block = 0;

  do {
    // Don't interpret until break is handled.
    if(breakfound) return;

    token_type = get_token();

    // See what kind of token is up.
    if(token_type == IDENTIFIER ||
       *token == INC || *token == DEC)
    {
      // Not a keyword, so process expression.
      putback();  // restore token to input stream for
                  // further processing by eval_exp()
      eval_exp(value); // process the expression
      if(*token != ';') throw InterpExc(SEMI_EXPECTED);
    }
    else if(token_type==BLOCK) { // block delimiter?
      if(*token == '{') { // is a block
        block = 1; // interpreting block, not statement
        // Record nested scope.
        nest_scope_stack.push(local_var_stack.size());
      }
      else { // is a }, so reset scope and return
        // Reset nested scope.
        local_var_stack.resize(nest_scope_stack.top());
        nest_scope_stack.pop();
        return;
      }
    }
    else // is keyword
      switch(tok) {
        case CHAR:
        case INT:     // declare local variables
          putback();
          decl_local();
          break;
        case RETURN:  // return from function call
          func_ret();
          return;
        case IF:      // process an if statement
          exec_if();
          break;
        case ELSE:    // process an else statement
          find_eob(); // find end of else block
                      // and continue execution
          break;
        case WHILE:   // process a while loop
          exec_while();
          break;
        case DO:      // process a do-while loop
          exec_do();
          break;
        case FOR:     // process a for loop
          exec_for();
          break;
        case BREAK:   // handle break
          breakfound = true;

          // Reset nested scope.
          local_var_stack.resize(nest_scope_stack.top());
          nest_scope_stack.pop();
          return;
        case SWITCH:  // handle a switch statement
          exec_switch();
          break;
        case COUT:    // handle console output
          exec_cout();
          break;
        case CIN:     // handle console input
          exec_cin();
          break;
        case END:
          exit(0);
      }
  } while (tok != END && block);
  return;
}

// Return the entry point of the specified function.
// Return NULL if not found.
char *find_func(char *name)
{
  unsigned i;

  for(i=0; i < func_table.size(); i++)
    if(!strcmp(name, func_table[i].func_name))
      return func_table[i].loc;

  return NULL;
}

// Declare a global variable.
void decl_global()
{
  token_ireps vartype;
  var_type vt;

  get_token(); // get type

  vartype = tok; // save var type

  // Process comma-separated list.
  do {
    vt.v_type = vartype;
    vt.value = 0; // init to 0
    get_token(); // get name

    // See if variable is a duplicate.
    for(unsigned i=0; i < global_vars.size(); i++)
      if(!strcmp(global_vars[i].var_name, token))
        throw InterpExc(DUP_VAR);

    strcpy(vt.var_name, token);
    global_vars.push_back(vt);

    get_token();
  } while(*token == ',');

  if(*token != ';') throw InterpExc(SEMI_EXPECTED);
}

// Declare a local variable.
void decl_local()
{
  var_type vt;

  get_token(); // get var type
  vt.v_type = tok; // store type

  vt.value = 0; // init var to 0

  // Process comma-separated list.
  do {
    get_token(); // get var name

    // See if variable is already the name
    // of a local variable in this scope.
    if(!local_var_stack.empty())
    for(int i=local_var_stack.size()-1;
        i >= nest_scope_stack.top(); i--)
    {
      if(!strcmp(local_var_stack[i].var_name, token))
        throw InterpExc(DUP_VAR);
    }

    strcpy(vt.var_name, token);
    local_var_stack.push_back(vt);
    get_token();
  } while(*token == ',');

  if(*token != ';') throw InterpExc(SEMI_EXPECTED);
}

// Call a function.
void call()
{
  char *loc, *temp;
  int lvartemp;

  // First, find entry point of function.
  loc = find_func(token);

  if(loc == NULL)
    throw InterpExc(FUNC_UNDEF); // function not defined
  else {
    // Save local var stack index.
    lvartemp = local_var_stack.size();

    get_args(); // get function arguments
    temp = prog; // save return location

    func_call_stack.push(lvartemp); // push local var index

    prog = loc; // reset prog to start of function
    get_params(); // load the function's parameters with
                  // the values of the arguments

    interp(); // interpret the function

    prog = temp; // reset the program pointer

    if(func_call_stack.empty()) throw InterpExc(RET_NOCALL);

    // Reset local_var_stack to its previous state.
    local_var_stack.resize(func_call_stack.top());
    func_call_stack.pop();
  }
}

// Push the arguments to a function onto the local
// variable stack.
void get_args()
{
  int value, count, temp[NUM_PARAMS];
  var_type vt;

  count = 0;
  get_token();
  if(*token != '(') throw InterpExc(PAREN_EXPECTED);

  // Process a comma-separated list of values.
  do {
    eval_exp(value);
    temp[count] = value; // save temporarily
    get_token();
    count++;
  } while(*token == ',');
  count--;

  // Now, push on local_var_stack in reverse order.
  for(; count>=0; count--) {
    vt.value = temp[count];
    vt.v_type = ARG;
    local_var_stack.push_back(vt);
  }
}

// Get function parameters.
void get_params()
{
  var_type *p;
  int i;

  i = local_var_stack.size()-1;

  // Process comma-separated list of parameters.
  do {
    get_token();
    p = &local_var_stack[i];
    if(*token != ')' ) {
      if(tok != INT && tok != CHAR)
        throw InterpExc(TYPE_EXPECTED);

      p->v_type = tok;
      get_token();

      // Link parameter name with argument already on
      // local var stack.