Re: [Dev-C++] delete statement gives segmentation fault error

[David M. <ci...@ya...>]

Hmm, it works fine for me.

I tried a few changes to your main() which follow:

int main(int argc, char* argv[])
{
   argv[0] = "dc";
   argv[1] = "rate = 2.5; distance = rate * 5;";
   argc = 2;
   switch (argc) {
     case 1:
       input = &cin  ;
       break;
     case 2:
       //Modified
       input = new istringstream(argv[1]);
       if(input == NULL) {
         cout << "Error with new" << endl;
         return 1;
       }
       if(!input->good()) {
         cout << "Stringstream not created properly" <<
endl;
       }
       break;
     default:
       error("too many arguements");
       return 1;
   }
   table ["pi"] = 3.1415926535897932385;
   table ["e"] = 2.718281828459042354;

   while (*input) {
     get_token();
     if (curr_tok == END) break;
     if (curr_tok == PRINT) continue;
     cout << expr(false) << '\n';
   }

   if (input != cin) {
     //Modified
     cout << "About to delete input" << endl;
     delete input;
   }
   //Modified
   system("PAUSE");
   return no_of_errors;
}

My only other change is instead of including
#include <strstream>
I included
#include <sstream>

Your code should work fine though. All I did was do some
error checking to
see if something is going wrong before we reach the delete.

----- Original Message ----- 
From: "Dawood Vora" <da...@ku...>
To: "Dev C++" <dev...@li...>
Sent: Thursday, August 14, 2003 8:39 PM
Subject: [Dev-C++] delete statement gives segmentation
fault error


> Hello every body,
> below is a straight code from Stroustrup's classic.  I am
running
> bloodshed DEV-C++. At the end, it is trying to delete the
object "input"
> using delete statement.  It straightaway gives me invalid
memory or
> segmentation fault error.  Also, if I comment the delete
statement, the
> code works fine as it should be.  Actually it happens,
only when I try to
> pass the command line arguement. As u all know, it is the
famous
calculator
> example from the 6th chapter of the book.  Right now, I
am in the 6th
> chapter, so I do not have a very good idea about new and
delete
> statements.  According to me the code should work, as we
are trying to
> delete the object we explicitly created.
>
> #include <iostream>
> #include <string>
> #include <map>
> #include <cctype>
> #include <strstream>
>
> enum Token_value{
>        NAME, NUMBER,END,
>        PLUS = '+',MINUS = '-', MUL = '*', DIV = '/',
>        PRINT = ';', ASSIGN = '=', LP = '(', RP = ')'
> };
>
> Token_value curr_tok  = PRINT;
>
> double number_value;
> string string_value;
> istream* input;
>
>
> int no_of_errors;
> double error(const string& s) {
>    no_of_errors++;
>    cerr<<"error: "<<s<<'\n';
>    return 1;
> }
>
> Token_value get_token() {
>    char ch;
>    do { // skip whitespace except \n
>        if (!((*input).get(ch))) return curr_tok = END;
>    } while (ch!= '\n' && isspace(ch));
>
>    switch (ch) {
>    case ';':
>    case '\n':
>      return curr_tok = PRINT;
>    case '*':
>    case '/':
>    case '+':
>    case '-':
>    case '(':
>    case ')':
>    case '=':
>      return curr_tok = Token_value(ch);
>
>    case '0':
>    case '1':
>    case '2':
>    case '3':
>    case '4':
>    case '5':
>    case '6':
>    case '7':
>    case '8':
>    case '9':
>    case '.':
>      (*input).putback(ch);
>      (*input)>> number_value;
>      return curr_tok = NUMBER;
>    default:
>      if (isalpha(ch)) {
>        string_value = ch;
>        while ((*input).get(ch) && isalnum(ch))
>           string_value+=ch;
>        (*input).putback(ch);
>        return curr_tok = NAME;
>      }
>      error ("bad token");
>      return curr_tok = PRINT;
>    }
> }
>
> //------------------------------------------------
prim(bool get)
> double expr(bool);
> map<string,double>table;
>
> double prim(bool get) {   // handle primaries
>    if (get) get_token();
>
>    switch(curr_tok){
>    case NUMBER:       //floating point constant
>    {
>      double v = number_value;
>      get_token();
>      return v;
>    }
>    case NAME:
>    {
>      double& v = table[string_value];
>      if (get_token() == ASSIGN)
>        v = expr(true);
>      return v;
>    }
>    case MINUS:  // unary minus
>      cout<<"reading negative number\n";
>      return  -prim(true);
>    case LP:
>    {
>      double  e =  expr(true);
>      if (curr_tok != RP) return error("')' expected");
>      get_token();  //eat ')'
>      return e;
>    }
>    default:
>      return error ("primary expected");
>    }
> }
>
> //------------------------------------------------
term(bool get)
> double term(bool get){          // multiply and divide
>    double left = prim(get);
>
>    for (;;)
>      switch (curr_tok) {
>      case MUL:
>        left *= prim(true);
>        break;
>      case DIV:
>        if (double d = prim(true)) {
>          left /= d;
>          break;
>        }
>        return error("divide by zero");
>      default:
>        return left;
>      }
> }
>
> //------------------------------------------------
expr(bool get)
> double expr(bool get) {      // add and subtract
>    double left = term(get);
>
>    for(;;)                     //forever
>      switch (curr_tok) {
>      case PLUS:
>        left += term(true);
>        break;
>      case MINUS:
>        left -= term(true);
>        break;
>      default:
>        return left;
>    }
> }
>
>
> int main(int argc, char* argv[])
> {
>    argv[0] = "dc";
>    argv[1] = "rate = 2.5; distance = rate * 5;";
>    argc = 2;
>    switch (argc) {
>      case 1:
>        input = &cin  ;
>        break;
>      case 2:
>        input = new istrstream(argv[1]);
>        break;
>      default:
>        error("too many arguements");
>        return 1;
>    }
>    table ["pi"] = 3.1415926535897932385;
>    table ["e"] = 2.718281828459042354;
>
>    while (*input) {
>      get_token();
>      if (curr_tok == END) break;
>      if (curr_tok == PRINT) continue;
>      cout << expr(false) << '\n';
>    }
>
>    if (input != cin) delete input;
>    return no_of_errors;
>
>        system("PAUSE");
>        return 0;
> }
>
>
>
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