file doesn't open, running outside of debugger results in seg fault (c++)

Question

Hello (and thanks in advance)

I'm in a bit of a quandry, I cant seem to figure out why I'm seg faulting.

A couple of notes:

1. It's for a course -- and sadly I am required to use use C-strings instead of std::string.
2. Please dont fix my code (I wont learn that way and I will keep bugging you). please just point out the flaws in my logic and suggest a different function/way.
3. platform: gcc version 4.4.1 on Suse Linux 11.2 (2.6.31 kernel)

Here's the code

main.cpp:

// ///////////////////////////////////////////////////////////////////////////////////
// INCLUDES (C/C++ Std Library)
#include    <cstdlib>      /// EXIT_SUCCESS, EXIT_FAILURE
#include    <iostream>     /// cin, cout, ifstream
#include    <cassert>      /// assert



// ///////////////////////////////////////////////////////////////////////////////////
// DEPENDENCIES (custom header files)
#include    "dict.h"       /// Header for the dictionary class





// ///////////////////////////////////////////////////////////////////////////////////
// PRE-PROCESSOR CONSTANTS
#define     ENTER    '\n'     /// Used to accept new lines, quit program.
#define     SPACE    ' '      /// One way to end the program




// ///////////////////////////////////////////////////////////////////////////////////
// CUSTOM DATA TYPES

/// File Namespace -- keep it local
namespace
{
   /// Possible program prompts to display for the user.
   enum  FNS_Prompts     
   {
      fileName_,     /// prints out the name of the file
      noFile_,       /// no file was passed to the program
      tooMany_,      /// more than one file was passed to the program
      noMemory_,     /// Not enough memory to use the program
      usage_,        /// how to use the program
      word_,         /// ask the user to define a word.
      notFound_,     /// the word is not in the dictionary
      done_,         /// the program is closing normally
   };

}


// ///////////////////////////////////////////////////////////////////////////////////
// Namespace
using    namespace   std;     /// Nothing special in the way of namespaces




// ///////////////////////////////////////////////////////////////////////////////////
// FUNCTIONS

/** prompt()   prompts the user to do something, uses enum Prompts for parameter.
*/
void  prompt(FNS_Prompts    msg   /** determines the prompt to use*/)
{
   switch(msg)
      {
         case  fileName_   :
            {
               cout << ENTER << ENTER << "The file name is: ";
               break;
            }
         case  noFile_     :
            {
               cout << ENTER << ENTER << "...Sorry, a dictionary file is needed.  Try again." << endl;
               break;
            }
         case  tooMany_    :
            {
               cout << ENTER << ENTER << "...Sorry, you can only specify one dictionary file.  Try again." << endl;
               break;
            }
         case  noMemory_   :
            {
               cout << ENTER << ENTER << "...Sorry, there isn't enough memory available to run this program." << endl;
               break;
            }
         case  usage_   :
            {
               cout << "USAGE:" << endl
                  << "    lookup.exe   [dictionary file name]" << endl << endl;
               break;
            }
         case  done_       :
            {
               cout << ENTER << ENTER << "like Master P says, \"Word.\"" << ENTER << endl;
               break;
            }
         case  word_       :
            {
               cout << ENTER << ENTER << "Enter a word in the dictionary to get it's definition." << ENTER
                  << "Enter \"?\" to get a sorted list of all words in the dictionary." << ENTER
                  << "... Press the Enter key to quit the program: ";
               break;
            }
         case  notFound_   :
            {
               cout << ENTER << ENTER << "...Sorry, that word is not in the dictionary." << endl;
               break;
            }
         default           :
            {
               cout << ENTER << ENTER << "something passed an invalid enum to prompt(). " << endl;
               assert(false);    /// something passed in an invalid enum
            }
      }
}




/** useDictionary()  uses the dictionary created by createDictionary
 * - prompts user to lookup a word
 * - ends when the user enters an empty word
 */
void    useDictionary(Dictionary    &d)
{
   char  *userEntry = new char;  /// user's input on the command line
   if(   !userEntry     )        // check the pointer to the heap
      {  cout << ENTER << MEM_ERR_MSG << endl;     exit(EXIT_FAILURE);
      }

   do
      {
         prompt(word_);
         // test code
         cout << endl << "----------------------------------------" << endl
            << "Enter something: ";

         cin.getline(userEntry,  INPUT_LINE_MAX_LEN,  ENTER);

         cout << ENTER << userEntry << endl;

      }while (  userEntry[0] != NIL    &&    userEntry[0] != SPACE  );

   // GARBAGE COLLECTION
   delete[] userEntry;

}




/** Program Entry
 * Reads in the required, single file from the command prompt.
 * - If there is no file, state such and error out.
 * - If there is more than one file, state such and error out.
 * - If there is a single file:
 *    - Create the database object
 *    - Populate the database object
 *    - Prompt the user for entry
 * main() will return EXIT_SUCCESS upon termination.
 */
int   main(int    argc,    /// the number of files being passed into the program
           char   *argv[]  /// pointer to the filename being passed into tthe program
          )
{

   // EXECUTE

   /* Testing code * /
         char  tempFile[INPUT_LINE_MAX_LEN] = {NIL};
         cout  << "enter filename: ";
         cin.getline(tempFile, INPUT_LINE_MAX_LEN, '\n');
   */
   // uncomment after successful debugging
   if(argc <= 1)
      {
            prompt(noFile_);     prompt(usage_);
            return   EXIT_FAILURE;  /// no file was passed to the program
      }
   else if(argc > 2)
      {
         prompt(tooMany_);    prompt(usage_);
         return   EXIT_FAILURE;  /// more than one file was passed to the program
      }
   else
      {
         prompt(fileName_);   cout << argv[1];  // print out name of dictionary file

         if(   !argv[1]    )
            {
            prompt(noFile_);     prompt(usage_);
            return   EXIT_FAILURE;  /// file does not exist
            }
         /*
            file.open( argv[1] );                  // open file
            numEntries >> in.getline(file);        // determine number of dictionary objects to create
            file.close();                          // close file
            Dictionary[ numEntries ](argv[1]);     // create the dictionary object
         */

         // TEMPORARY FILE FOR TESTING!!!!
         //Dictionary  scrabble(tempFile);

         Dictionary  scrabble(argv[1]);         // creaate the dicitonary object
         //*/
         useDictionary(scrabble);               // prompt the user, use the dictionary
      }

   // exit
   return   EXIT_SUCCESS;     /// terminate program.
}

Dict.h/.cpp

#ifndef  DICT_H
#define  DICT_H


// ///////////////////////////////////////////////////////////////////////////////////
// DEPENDENCIES (Custom header files)
#include    "entry.h"   /// class for dictionary entries


// ///////////////////////////////////////////////////////////////////////////////////
// PRE-PROCESSOR MACROS
#define  INPUT_LINE_MAX_LEN   256   /// Maximum length of each line in the dictionary file


class  Dictionary
{
  public  :

      //
      // Do NOT modify the public section of this class
      //

      typedef void  (*WordDefFunc)(const char  *word, const char  *definition);

      Dictionary( const char  *filename );
      ~Dictionary();

      const char  *lookupDefinition( const char  *word );

      void  forEach( WordDefFunc  func );

   private  :

      //
      // You get to provide the private members
      //

      // VARIABLES

      int      m_numEntries;        /// stores the number of entries in the dictionary
      Entry    *m_DictEntry_ptr;    /// points to an array of class Entry

      // Private Functions

};

#endif
-----------------------------------
// ///////////////////////////////////////////////////////////////////////////////////
// INCLUDES (C/C++ Std Library)
#include    <iostream>     /// cout, getline
#include    <fstream>      // ifstream
#include    <cstring>      /// strchr



// ///////////////////////////////////////////////////////////////////////////////////
// DEPENDENCIES (custom header files)
#include    "dict.h"       /// Header file required by assignment
//#include    "entry.h"      /// Dicitonary Entry Class


// ///////////////////////////////////////////////////////////////////////////////////
// PRE-PROCESSOR MACROS
#define  COMMA    ','   /// Delimiter for file
#define  ENTER    '\n'  /// Carriage return character

#define  FILE_ERR_MSG   "The data file could not be opened.  Program will now terminate."

#pragma     warning(disable : 4996)    /// turn off MS compiler warning about strcpy()


// ///////////////////////////////////////////////////////////////////////////////////
// Namespace reference
using    namespace   std;


// ///////////////////////////////////////////////////////////////////////////////////
// PRIVATE MEMBER FUNCTIONS

/**
 * Sorts the dictionary entries.
*/
/*
   static   void  sortDictionary(?)
   {
     // sort through the words using qsort

   }
*/


/**   NO LONGER NEEDED??
 * parses out the length of the first cell in a delimited cell
 * /
int   getWordLength(char  *str       /// string of data to parse
                    )
{
   return strcspn(str, COMMA);
}
 */


// ///////////////////////////////////////////////////////////////////////////////////
// PUBLIC MEMBER FUNCTIONS

/** constructor for the class
*  - opens/reads in file
*  - creates initializes the array of member vars
*  - creates pointers to entry objects
*  - stores pointers to entry objects in member var
*  - ? sort now or later?
*/
Dictionary::Dictionary( const char  *filename )
   {
      // Create a filestream, open the file to be read in
      ifstream    dataFile(filename,   ios::in );

      /*
      if(   dataFile.fail()   )
         {  cout << FILE_ERR_MSG << endl;    exit(EXIT_FAILURE);
         }
      */

      if(   dataFile.is_open()   )
         {
            // read first line of data
            // TEST CODE in.getline(dataFile,   INPUT_LINE_MAX_LEN)  >> m_numEntries;
            // TEST CODE char  temp[INPUT_LINE_MAX_LEN]   = {NIL};
            // TEST CODE dataFile.getline(temp,INPUT_LINE_MAX_LEN,'\n');
            dataFile >> m_numEntries;  /** Number of terms in the dictionary file
                                  *  \todo find out how many lines in the file, subtract one, ingore first line
                                  */

            //create the array of entries
            m_DictEntry_ptr   =  new   Entry[m_numEntries];

            // check for valid memory allocation
            if(   !m_DictEntry_ptr   )
               {  cout << MEM_ERR_MSG << endl;     exit(EXIT_FAILURE);
               }

            // loop thru each line of the file, parsing words/def's and populating entry objects

            for(int EntryIdx = 0;   EntryIdx < m_numEntries;   ++EntryIdx)
               {
                  // VARIABLES               
                  char  *tempW_ptr;    /// points to a temporary word
                  char  *tempD_ptr;    /// points to a temporary def
                  char  *w_ptr;        /// points to the word in the Entry object
                  char  *d_ptr;        /// points to the definition in the Entry

                  int   tempWLen;      /// length of the temp word string
                  int   tempDLen;      /// length of the temp def string

                  char  tempLine[INPUT_LINE_MAX_LEN] = {NIL};  /// stores a single line from the file


                  // EXECUTE
                  // getline(dataFile, tempLine)            // get a "word,def" line from the file
                  dataFile.getline(tempLine, INPUT_LINE_MAX_LEN);    // get a "word,def" line from the file

                  // Parse the string
                  tempW_ptr = tempLine;                  // point the temp word pointer at the first char in the line
                  tempD_ptr = strchr(tempLine, COMMA);   // point the def pointer at the comma
                  *tempD_ptr = NIL;                      // replace the comma with a NIL
                  ++tempD_ptr;                           // increment the temp def pointer

                  // find the string lengths... +1 to account for terminator
                  tempWLen = strlen(tempW_ptr)  + 1;
                  tempDLen = strlen(tempD_ptr)  + 1;

                  // Allocate heap memory for the term and defnition
                  w_ptr    =  new char[ tempWLen ];
                  d_ptr    =  new char[ tempDLen ];

                  // check memory allocation
                  if(   !w_ptr   &&    !d_ptr   )
                     {  cout << MEM_ERR_MSG << endl;     exit(EXIT_FAILURE);
                     }

                  // copy the temp word, def into the newly allocated memory and terminate the strings
                  strcpy(w_ptr,tempW_ptr);   w_ptr[tempWLen] = NIL;
                  strcpy(d_ptr,tempD_ptr);   d_ptr[tempDLen] = NIL;

                  // set the pointers for the entry objects
                  m_DictEntry_ptr[ EntryIdx ].setWordPtr(w_ptr);
                  m_DictEntry_ptr[ EntryIdx ].setDefPtr(d_ptr);
               }

            // close the file
            dataFile.close();
         }

      else
         {  cout << ENTER << FILE_ERR_MSG << endl;    exit(EXIT_FAILURE);
         }
   }


/**
 * cleans up dynamic memory
 */
Dictionary::~Dictionary()
   {
      delete[]    m_DictEntry_ptr;  /// thou shalt not have memory leaks.
   }


/**
 * Looks up definition
 */
/*
const char  *lookupDefinition( const char  *word )
   {
     // print out the word ---- definition
   }
 */

/**
 * prints out the entire dictionary in sorted order
 */
/*
void  forEach( WordDefFunc  func )
  {
      // to sort before or now.... that is the question
  }
*/

Entry.h/cpp

#ifndef     ENTRY_H
#define     ENTRY_H

// ///////////////////////////////////////////////////////////////////////////////////
// INCLUDES (C++ Std lib)
#include    <cstdlib>      /// EXIT_SUCCESS, NULL

// ///////////////////////////////////////////////////////////////////////////////////
// PRE-PROCESSOR MACROS
#define  NIL            '\0'  /// C-String terminator
#define  MEM_ERR_MSG    "Memory allocation has failed.  Program will now terminate."


// ///////////////////////////////////////////////////////////////////////////////////
// CLASS DEFINITION
class    Entry
{
   public:
      Entry(void) : m_word_ptr(NULL), m_def_ptr(NULL) {  /* default constructor */  };

      void  setWordPtr(char  *w_ptr);  /// sets the pointer to the word - only if the pointer is empty
      void  setDefPtr(char  *d_ptr);   /// sets the ponter to the definition - only if the pointer is empty

      /// returns what is pointed to by the word pointer
      char  getWord(void)  const    {  return   *m_word_ptr;    }

      /// returns what is pointed to by the definition pointer
      char  getDef(void)   const    {  return   *m_def_ptr;     }

   private:

      char  *m_word_ptr;   /** points to a dictionary word */
      char  *m_def_ptr;     /** points to a dictionary definition */
};

#endif
--------------------------------------------------
// ///////////////////////////////////////////////////////////////////////////////////
// DEPENDENCIES (custom header files)
#include    "entry.h"      /// class header file

// ///////////////////////////////////////////////////////////////////////////////////
// PUBLIC FUNCTIONS

/*
 * only change the word member var if it is in its initial state
 */
void  Entry::setWordPtr(char  *w_ptr)
{
   if(m_word_ptr == NULL)
      {  m_word_ptr = w_ptr;
      }
}



/*
 * only change the def member var if it is in its initial state
 */
void  Entry::setDefPtr(char  *d_ptr)
{
   if(m_def_ptr == NULL)
      {  m_word_ptr = d_ptr;
      }
}

Answer 1

You are allocation single character for user entry, while it could be a lot bigger. Use char *userEntry = new char[MAX_PATH] instead

Answer 2

The previous post picked out the likely immedate cause of the segfault, you need INPUT_LINE_MAX_LEN+1 bytes to store the input. But in this function there is no reason nto new/delete in the first place, just use char userEntry[INPUT_LINE_MAX_LEN+1]; on the stack

Also note that you do have a memory leaks -- the Entry class owns the pointers, but does not delete them. Since you are not copying anything, then just adding the delete statements to this class will work.

I hope that the intent of this assigment is to illustrate just why we avoid new[]/delete[] and the ilk in modern C++. If this were a Java course, this would be like programming something in AWT 1.0 just to demonstrate why it was replaced years ago. The things is, that many instructors are instructors because they can profess to have used C++ "for 15+ years." More often than not, sad to say, this means "I write C++ as if it were 1995." Pick up "Accelerated C++" for a good beginners into to C++ that uses the libraries.

Answer 3

Easy Problems

The easy problem to spot is here:

cin.getline(userEntry,  INPUT_LINE_MAX_LEN,  ENTER); 

The first problem is that unless INPUT_LINE_MAX_LEN == 1 then the line is wrong.
This is easy to fix change the declaration og userEntry to:

userEntry = new char[INPUT_LINE_MAX_LEN + 1];

The second problem I see is:

// GARBAGE COLLECTION   
delete[] userEntry; 

Which is wrong because you only allocate a single char not an array of char for userEntry. The same solution as above.

A better solution is to use a managed array of characters (i.e. a string)

std::string    userEntry;
std::getline(std::cin,userEntry);

No need to allocate or delete and it re-sizes as required so you can't write off then end.

Other worries:

Seeing this in C++ code makes the hares on the back of my nech stand up:

typedef void  (*WordDefFunc)(const char  *word, const char  *definition); 

In C++ it is much easier to use interfaces rather than function pointers. (Yes I know C++ does not have the keyword interface. But the concept of an interface is the same in all languages it is a class definition that implements a specific contract).

class IFuncAction
{
    virtual void action(char const* word,char const* definition) = 0;
};

You do way too much memory management in the class.
I can already see several memory leaks (if I look harder I am sure I will spot pointers to non existant objects that have gone out of scope).

A modern C++ program will have very few pointers in it.

• Replace your "const char*" and your "char*" with std::string.
• Replace your manually created arrays with std::vector<>
• Oh. We already have a standard Dictionary. Look up std::map.

I will bet most of your problems will disapear if you stop trying to do manual memory management like this was a C program.

Dictionary::Dectionary

Ideally the dictionary constructor woudl look like this:

// Pass a stream to the constructor.
// Now a dictionary can be created from a file or
// a string (stringstream) when doing unit tests.
//
Dictionary::Dictionary(std::istream& data) 
{
    if (!data)
    {    throw MyProblemException("Bad Input to Dictionary constructor");
    }

    Entry  item;

    // While we can read data from the stream
    while(data >> item)
    {
        // Add it to the store
        m_DictEntry.push_back(item);
    }
} 

std::istream& operator>>(std::istream& str,Entry& data)
{
    std::getline(str,data.m_word, COMMA);
    std::getline(str,data.m_definition);

    return str;
}