NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part2/15565

Text File | 1996-08-05 | 10.0 KB | 427 lines

Path: nuscc.nus.sg!wongsiaw
From: [e-mail] (Virus)
Newsgroups: comp.lang.c++
Subject: [HELP!!!] Segmentation Fault!
Date: 6 Apr 1996 01:15:22 GMT
Organization: ...I am a wuggies...
Message-ID: <4k4gja$[e-mail]>
NNTP-Posting-Host: [e-mail]
X-Newsreader: TIN [version 1.2 PL2]

Help !!!
[This is going to be a very long mail, I sincerely hope that you can
read thro it to help a novice C++ programmer.]

I keep getting segmentation fault in my program, and I have tried using the
debugger (gdb in unix), but I cannot understand what the debugger is trying
to say..

[my story]
I have 2 files, that I am suppose to read in, one is space-separated and
the other is comma-separated. In each of the files, there are student
records, each terminated by a "end".

This is the space-separated file, sfile.data .

space-separated

Undergrad "Khoo Kay Chong" 946788H13
IC252 90 IC251 95 IC205 85 end

Graduate "Lee Su Shi"   901234N13 Master TA
IC401 80 IC501  85 end

Graduate "James Bond"     880007N13 PhD RA
IC405 85 IC504 90 IC512 95 end

Exchange "Tom Hanks" 905678N13 "Stanford University"
IC101 80 end


And the comma-separated file looks the same except that it uses the
comma to separate the fields of the record.

I am to write 3 classes, StudentFile, SpaceStudentFile and CommaStudentFile.
I have already done those, but I ran into segmentation fault when I
try to run my compiled program.

here are the files..

If you think you need to see Student.h, Student.c String.h, String.c,
ExchStudent.h ExchStudent.c, GradStudent.h, GradStudent.c, pls e-mail
me and let me know.

I really appreciate your help, as this is only part of my program.
I still have other classes to write that access this class to hand in
my final program. (but currently I am stuck here !!!)

Thanx!!!

regards,
Diana
ps : I hope that all the comments is sufficient for you to understand my
     codes.

-------------------------------------------------------------------------

//StudentFile.h

// Need to put "virtual" in front of the object name  and
// make it = 0 if it is a deferred obj

#ifndef StudentFile_h
#define StudentFile_h

#include "Student.h"


// Constants that needed to be used in the program
#define UNDERGRAD    "Undergrad"
#define GRADUATE    "Graduate"
#define EXCHANGE    "Exchange"
#define PHD        "PhD"
#define MASTER        "Master"
#define SCHOLARSHIP    "Scholarship"
#define TEACH        "Teach"
#define RESEARCH    "Research"
#define NONE        "None"
#define END        "end"

class StudentFile
{
public :
    // Public deferred method
    // For opening a file for reading
    // Opens the file by the name filename for reading
    // if file exists, can be opened and the opened file has the
    // correct file-type, then it returns non-0 (true)
    // Otherwise, returns 0 (false)
    virtual int open (const char *filename) = 0;

    // Public deferred method
    // For closing a file
    virtual void close () = 0;

    // Public polymorphic (non-deferred) method
    // For reading a student's record
    // Reads the next student's record, stores it in a dynamically
    // created instance, and returns a pointer to the instance
    // The dynamically created instance should belong to either
    // Student, GradStudent, ExchStudent class depending on the
    // student-type
    // Returns NULL if there is no more record in the file
    Student *readNextRecord ();

protected :
    // Protected deferred method
    // For reading a field from the file
    // Reads the next field from the file and returns a pointer
    // to the field
    // This method is used to support readNextRecord
    virtual char *readNextField ()  = 0;


    FILE *fd;
};

#endif


-----------------------------------------------------------------------

// I think the problem is here !!!
// StudentFile.c

#include <string.h>
#include "StudentFile.h"
#include "GradStudent.h"
#include "ExchStudent.h"


// Public polymorphic (non-deferred) method
// For reading a student's record
// Reads the next student's record, stores it in a dynamically
// created instance, and returns a pointer to the instance
// The dynamically created instance should belong to either
// Student, GradStudent, ExchStudent class depending on the
// student-type
// Returns NULL if there is no more record in the file

Student* StudentFile::readNextRecord ()
{
  Student *Stud;
  char *field1, *field2, *field3, *field4, *field5;

  // field1 - field5 are used for reading in of diff fields in a record
  // field1 read in from the record, this field now states the student-type


//  strcpy(field1, readNextField());
  field1 = (readNextField());

    printf("%s\n",field1); //debug stmt


  if (field1 == NULL) return NULL;
  // nothing to read in

    printf("%s\n",field1);//debug stmt

  field2 = (readNextField());
  // next field is the StudName, so get the Student name in a record

    printf("%s\n",field2);//debug stmt

    printf("%s %s \n", field1, field2);
  field3 = strdup(readNextField());
  // get the Student number in a record

    printf("%s\n",field3);//debug stmt

  // field1 has already read in the Student type, ie Graduate, Exchange, etc
  // so now need to check what is being read in

    printf("%s\n", field1);//debug stmt

    // BIG problem !!! field1 now actually has the content of
    // field3 !!! in fact all the field1, field2 and field3 has the
    // same content !!! WHY????

  // Check for Undergraduates
  if (!strcmp(field1, "Undergrad")) {
    printf("Create Undergrad here!\n");
    Stud = new Student(field2, field3);
  // The student type read in is Undergrade, an instance of Student class
  // will be created, and field2 = StudName, field3 = StudNo

    printf("Undergrad created!\n");
  }

  // Check for Graduates
  else if (!strcmp(field1, GRADUATE))
  {
    int Stud_lvl, Assist_type;

  // Now check the Gradute level
        if (!strcmp(field4 = readNextField(), PHD))
            Stud_lvl = GradStudent::PhD;
        else if (!strcmp(field4, MASTER))
            Stud_lvl = GradStudent::Master;

  // Now check the assistant-ship, make field4 read the next field
        if (!strcmp(field4 = readNextField(), TEACH))
            Assist_type = GradStudent::TA;
        else if (!strcmp(field4, SCHOLARSHIP))
            Assist_type = GradStudent::Scholarship;
        else if (!strcmp(field4, RESEARCH))
            Assist_type = GradStudent::RA;
        else if (!strcmp(field4, NONE))
            Assist_type = GradStudent::None;

  // An instance of GradStudent class will be created
        GradStudent *Grad = new GradStudent(field2, field3, Stud_lvl, Assist_type);
  // field2 = StudName, field3 = StudNo,
        Stud = Grad;
  }

  // Check for Exchange Students
  else if (!strcmp(field1, EXCHANGE))
  {
  // An instance of ExchStudent class will be created
        ExchStudent *Exch = new ExchStudent(field2, field3, readNextField());
  // field2 = StudName, field3 = StudNo, readNextField() = parentU
        Stud = Exch;
  }

  // Now read course names and grades
  while (!strcmp(field5 = readNextField(), END))
  {
    int Course_Gr;

    // read the grade of the course
    sscanf(readNextField(), "%i", &Course_Gr);
    // field5 = course_name
    Stud -> assignGrade(field5, Course_Gr);
  }

  return Stud;
} // end of readNextRecord

-------------------------------------------------------------------------

// SpaceStudentFile.h

#ifndef SpaceStudentFile_h
#define SpaceStudentFile_h

#include "StudentFile.h"

class SpaceStudentFile : public StudentFile
{
public :
    // Open the cfile.data for reading..
    int open (const char *filename);

    // Close the file after reading
    void close ();

private :

    // Read the next field from the file - record
    char *readNextField();

};

#endif


// SpaceStudentFile.c

#include "SpaceStudentFile.h"

// Fields in sfile.data are seperated by one or more spaces

int SpaceStudentFile::open (const char *filename)
{
  char buffer[20];

  fd = fopen (filename, "r");
  if (fd == NULL) {
    printf("Cannot open file : %s \n", filename);
    return 0;
  }
  fscanf(fd, "%s", buffer);
  return(!strcmp(buffer, "space-separated"));
}


void SpaceStudentFile::close ()
{
  fclose(fd);
}

char* SpaceStudentFile::readNextField()
{
  char str[40];
  int i = 0;

  // take away starting whitespaces
  while (str[0] = fgetc(fd)) {
      if (*str == ' ') continue;
    if (*str == '\t') continue;
    if (*str == '\n') continue;
    if (*str == EOF) return NULL;
    break;
  }

  // read from " to next "
  if (str[0] == '"') {
    for (i=0; ((str[i] = fgetc(fd)) != '"'); i++)
    ;
    str[i]=0;
    return str;
  }

  // else read until next whitespace
  for (i=1; ((str[i] = fgetc(fd)) != ' ')
    && (str[i] != '\n') && (str[i] != '\t'); i++)
  ;
  str[i] = 0;
  return str;


}

----------------------------------------------------------------------

// CommaStudentFile.h

#ifndef CommaStudentFile_h
#define CommaStudentFile_h

#include "StudentFile.h"

class CommaStudentFile : public StudentFile
{
public :
    // Open the cfile.data for reading..
    int open (const char *filename);

    // Close the file after reading
    void close ();

private :

    // Read the next field from the file - record
    char *readNextField();

};

#endif

----------------------------------------------------------------------

// CommaStudentFile.c

#include "CommaStudentFile.h"

// Fields in cfile.data are seperated by whitespaces and commas

int CommaStudentFile::open (const char *filename)
{
  char buffer[20];

  fd = fopen(filename, "r");
  if (fd == NULL) {
    printf("Cannot open file :%s\n", filename);
    return 0;
  }
  fscanf(fd, "%s", buffer);
  return (!strcmp(buffer, "comma-separated"));

}


void CommaStudentFile::close()
{
  fclose(fd);
}

char* CommaStudentFile::readNextField()
{
  char str[40];
  int i=0;

  // take away whitespace, for more comments, see SpaceStudentFile.c
  while (str[0] = fgetc(fd)) {
    if (*str == ' ') continue;
    if (*str == '\n') continue;
    if (*str == '\t') continue;
    if (*str == EOF) return "EOF";
    break;
  }

  // read until next comma
  for (i=0; ((str[i]=fgetc(fd)) != ',') && (str[i] != '\n'); i++)
  {    printf("%d",i); }
  ;
  printf("\n");
  str[i] =0;

  // take away trailing whitespace
  for (; (str[i-1] == ' '); i--);
  str[i+1] = 0;

  return str;


}

------------------------------------------------------------------------


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