Need a help with C code-Segmentation Fault

nkhambal · #1 16-Jul-2004, 16:30

Hi guys,

Just started learning C a few days back.Working on following code with structures.But when i execute i get segmentation fault.Could some one pls help with this ? Right now only choice "1"(Add Record) is being coded.

CPP / C++ / C Code:

#include <stdio.h>
typedef struct emprec
	{
		unsigned short int empno;
		char *name;
		char *dob;
		char *doj;
		char *location;
		float salary;
	}emp;
emp *records;
void add_record(emp *records);
/*void view_record(int empno,emp record);
void modify_record(int empno,emp record);
void delete_record(int empno,emp record);
void report(emp records[]);*/
#define MAX_RECORDS 10
int main()
{	
	int choice,loop;
	printf("\t\t          *Employee records systems*              \n");
	printf("1. Add a record\n");
	printf("2. View a record\n");
	printf("3. Modify a record\n");
	printf("4. Delete a record\n");
	printf("5. Report\n");
	printf("6. Exit\n");
	
	do
	{
	printf("Enter selecttion: ");
	scanf("%d",&choice);
	switch (choice)
	{
	case 1: 	add_record(records);
				loop=1;
				break;
	case 2:		view_record();
				loop=1;
				break;
	case 3:		modify_record();
				loop=1;
				break;
	case 4:		delete_record();
				loop=1;
				break;
	case 5:		report();
				loop=1;
				break;
	case 6:		printf("Thanks you.Bye\n");
				loop=0;
				break;
	default:	printf("Wrong Choice again\n");
				loop=1;
	}
	}
	while (loop);
	return 0;
}
void add_record(emp *records)
{	static unsigned short int i=0;
	char *name;
	char *dob;
	char *doj;
	char *location;
	float salary;
	int add=1;
	i++;
	if (i == MAX_RECORDS)
	{
		printf("Last Empleyee\n");
	} else if (i>MAX_RECORDS)
	{
		printf("Sorry Max number of records reached\n");
		add=0;

	}
	if (add)
	{
		printf("Add record for Employee no: %d\n",i);
		printf("\nEmployee Name: ");
		scanf("%100s",name);
		printf("Date Of Birth(mm-dd-yy): ");
		scanf("%20s",dob);
		printf("Date of Joining(mm/dd/yy): ");
		scanf("%20s",doj);
		printf("Employee Location: ");
		scanf("%20s",location);
		printf("Salary: ");
		scanf("%f",&salary);
		records[i].empno=i;
		printf(".");
		records[i].name=name;
		printf(".");
		records[i].dob=dob;
		printf(".");
		records[i].doj=doj;
		printf(".");
		records[i].location=location;
		printf(".");
		records[i].salary=salary;
		printf(".");
		printf("Record added to Database.");
	}
}
void delete_record()
{
	printf("Hi\n");
}
void modify_record()
{
	printf("Hi\n");
}
void view_record()
{
	printf("Hi\n");
}
void report()
{
	printf("Hi\n");
}

dsmith · #2 16-Jul-2004, 16:42

Hi nkhambal. Welcome to GIDForums.

If you are new to C, I would try to avoid using pointers until you are a bit more comfortable with C. For example, instead of:

CPP / C++ / C Code:

emp *records;

Make this an array of structures like:

CPP / C++ / C Code:

emp records[MAX_RECORDS]

The reason that you are getting a segfault is that you are trying to use unallocated memory. When you use, "emp* records", you are simply defining a memory address that will eventually point to a type of structure emp*, but you are not allocating any memory for this. So unless you want to use malloc & a list, I would recommend using an array. (Especially for something this small.)

In addition, when you define your structure, use arrays for now to get used to C and then go back and use pointers:

CPP / C++ / C Code:

typedef struct emprec
  {
    unsigned short int empno;
    char name[30];
    char dob[20];
    char doj[20];
    char location[50];
    float salary;
  }emp;

Now to add data, you can use something more like:

CPP / C++ / C Code:

printf("Add record for Employee no: %d\n",i);
printf("\nEmployee Name: ");
scanf("%s",records[i].name);

And so on...

Also, you may want to use fgets instead of scanf. It allows you to limit your input, like so:

CPP / C++ / C Code:

fgets(stdin,30,records[i].name);

Good luck!

nkhambal · #3 16-Jul-2004, 17:11

Thanks dsmith,
That was quick.

I made the changes in code.It works now.One small problem in fuction add_record below.

CPP / C++ / C Code:

void add_record(emp records[])
{	static unsigned short int i=0;
	int add=1;
	float sal;
	i++;
	if (i == MAX_RECORDS)
	{
		printf("Last Empleyee\n");
	} else if (i>MAX_RECORDS)
	{
		printf("Sorry Max number of records reached\n");
		add=0;

	}
	if (add)
	{
		printf("Add record for Employee no: %d\n",i);
		printf("\nEmployee Name: ");
		scanf("%s",records[i].name);
		printf("Date Of Birth(mm/dd/yy): ");
		scanf("%s",records[i].dob);
		printf("Date of Joining(mm/dd/yy): ");
		scanf("%s",records[i].doj);
		printf("Employee Location: ");
		scanf("%s",records[i].location);
		printf("Salary: ");
		scanf("%f",&sal);
		records[i].empno=i;
		printf("\n....");
		records[i].salary=sal;
		printf("....\n");
		printf("Record added to Database\n");
	}
}

when i try to run the program and try adding record program does not wait on Date of birth printf it goes to next printf for date of joining.Here is my output.

*Employee records systems*
1. Add a record
2. View a record
3. Modify a record
4. Delete a record
5. Report
6. Exit
Enter selecttion: 1
Add record for Employee no: 3

Employee Name: Johny English
Date Of Birth(mm/dd/yy): Date of Joining(mm/dd/yy):

Any suggetions ?

Thanks,

dsmith · #4 16-Jul-2004, 17:55

Hi nkhambal. I am glad that things are working.

I don't use scanf alot, especially in the situations of accepting user input as in the program you have. Scanf is better suited for structured input and reading files IMO.

Instead, I would recommend looking at fgets. I gave you the wrong format last time.

It is like this:

CPP / C++ / C Code:

char *fgets(char *s, int size, FILE *stream);

I would even get your floating point using a temporary string and then using atof to convert it to a floating point, ala:

CPP / C++ / C Code:

char temp[30];
printf("Enter Salary: ");
fgets(temp,29,stdin);
records[i].salary=(float) atof(temp);

See if fgets solves the problem. It is much more suitable for accepting user input.

nkhambal · #5 16-Jul-2004, 18:13

Hi dsmith,

Tried with fgets but still program does not hault at Printf plus i get complier error saying "incompatible types in assignment".Following are some changes I did,

CPP / C++ / C Code:

char name[100];
printf("\nEmployee Name: ");
fgets(name,50,stdin);
records[i].name=name;

It gives complier error for assignment statement.Where am i going wrong?

Thanks,

dsmith · #6 16-Jul-2004, 19:41

Quote:

Originally Posted by nkhambal

Hi dsmith,

Tried with fgets but still program does not hault at Printf plus i get complier error saying "incompatible types in assignment".Following are some changes I did,

CPP / C++ / C Code:

char name[100];
printf("\nEmployee Name: ");
fgets(name,50,stdin);
records[i].name=name;

It gives complier error for assignment statement.Where am i going wrong?

Thanks,

You can't assign c string (char arrays or char pointers) with the assignment operator. You need to use the strcpy command to copy the string from one memory location to another.

CPP / C++ / C Code:

strcpy(records[i].name,name);

Also, why are you using the seperate name variable? Is there a reason that you can't just use:

CPP / C++ / C Code:

fgets(record[i].name,50,stdin);

Is that giving you an error?

Also, can you post all of your data entry routine again? I am not sure why it is not stopping to allow for input if you have removed all of the scanfs...

nkhambal · #7 16-Jul-2004, 19:52

Hi dsmith,

Now the compilation error is gone.I am using records[i].variable in fgets.However the problem with printf is still there.Programs does not wait a printf for adding name.Following is my add record function

CPP / C++ / C Code:

void add_record(emp records[])
{	static unsigned short int i=0;
	int add=1;
	float sal;
	i++;
	if (i == MAX_RECORDS)
	{
		printf("Last Empleyee\n");
	} else if (i>MAX_RECORDS)
	{
		printf("Sorry Max number of records reached\n");
		add=0;

	}
	if (add)
	{
		printf("Add record for Employee no: %d\n",i);
		printf("\nEmployee Name:");
		fgets(records[i].name,50,stdin);
		printf("Date Of Birth(mm/dd/yy):");
		fgets(records[i].dob,50,stdin);
		printf("Date of Joining(mm/dd/yy):");
		fgets(records[i].doj,50,stdin);
		printf("Employee Location:");
		fgets(records[i].location,50,stdin);
		printf("Salary:");
		scanf("%f",&sal);
		records[i].empno=i;
		printf("....");
		records[i].salary=sal;
		printf("....\n");
		printf("Record added to Database\n");
	}
}

Thanks,

dsmith · #8 16-Jul-2004, 20:15

Quote:

Originally Posted by nkhambal

Hi dsmith,

Now the compilation error is gone.I am using records[i].variable in fgets.However the problem with printf is still there.Programs does not wait a printf for adding name.Following is my add record function

CPP / C++ / C Code:

void add_record(emp records[])
{	static unsigned short int i=0;
	int add=1;
	float sal;
	i++;
	if (i == MAX_RECORDS)
	{
		printf("Last Empleyee\n");
	} else if (i>MAX_RECORDS)
	{
		printf("Sorry Max number of records reached\n");
		add=0;

	}
	if (add)
	{
		printf("Add record for Employee no: %d\n",i);
		printf("\nEmployee Name:");
		fgets(records[i].name,50,stdin);
		printf("Date Of Birth(mm/dd/yy):");
		fgets(records[i].dob,50,stdin);
		printf("Date of Joining(mm/dd/yy):");
		fgets(records[i].doj,50,stdin);
		printf("Employee Location:");
		fgets(records[i].location,50,stdin);
		printf("Salary:");
		scanf("%f",&sal);
		records[i].empno=i;
		printf("....");
		records[i].salary=sal;
		printf("....\n");
		printf("Record added to Database\n");
	}
}

Thanks,

I apologize, but I don't use scanf often because of some of its weirdness and here is another one that I just found. If I use a fgets right after a scanf, the fgets will see the enter character from the previous scanf and think that the user has pressed enter.

Work-arounds:

Totally eliminate any calls to scanf
Totally eliminate any calls to fgets
Clear the input buffer in between calls to scanf & fgets with:
CPP / C++ / C Code:
fgetc(stdin);

Sorry, I mainly use fgets so I have never encountered this before.

Hope this does the trick.

WaltP · #9 16-Jul-2004, 20:20

CPP / C++ / C Code:

typedef struct emprec
  {
    unsigned short int empno;
    char name[30];
    char dob[20];
    char doj[20];
    char location[50];
    float salary;
  }emp;

Above is your structure. Your code:

CPP / C++ / C Code:

if (add)
{
	printf("Add record for Employee no: %d\n",i);
	printf("\nEmployee Name:");
	fgets(records[i].name,50,stdin);  // name is defined as 30 -- potential memory error here.
	printf("Date Of Birth(mm/dd/yy):");
	fgets(records[i].dob,50,stdin);  // same here.
	printf("Date of Joining(mm/dd/yy):");
	fgets(records[i].doj,50,stdin);  // ditto
	printf("Employee Location:");
	fgets(records[i].location,50,stdin);  // ditto
	printf("Salary:");
	scanf("%f",&sal);
	records[i].empno=i;
	printf("....");
	records[i].salary=sal;
	printf("....\n");
	printf("Record added to Database\n");
}

Make sure you specify the MAXIMUM number of characters to read, not just a value at random otherwise you can have major program crashes.

After you enter 1 person's data is that when you have the "printf" problem? If so, it's because you still have a scanf() in your code. That call leaves the '\n' in the input buffer. switch to:

CPP / C++ / C Code:

printf("Salary:");
fgets(buffer, 50, stdin);  // read the line (be sure to define buffer[50])
sscanf(buffer, "%f", &sal);// convert to float

nkhambal · #10 16-Jul-2004, 21:10

Hi dsmith,
Clearing buffer did the job...Problem is solved now.Heres what i did..

CPP / C++ / C Code:

if (add)
	{
		fgetc(stdin);
		printf("Add record for Employee no: %d\n",i);
		printf("\nEmployee Name:");
		fgets(records[i].name,50,stdin);

Thanks for your help..

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Rate This Thread
Rate This Thread:

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Re: Formatting C / C++ code	WaltP	C Programming Language	1	07-Jan-2008 00:59
very difficult code - program	gaurav_sting	C++ Forum	1	16-Jun-2004 01:59
Explain code in MS STL's binary_search	rom	C++ Forum	11	07-Mar-2004 21:11
child pid xxx exit signal Segmentation fault (11)	bezak	Apache Web Server Forum	1	24-Nov-2003 10:18