Help with dynamically allocated array of pointer to a structure.

[cmasri]

bool AddRecord(StudentRecord**& Records, int& numRecords){	
	struct StudentRecord
{
	char* firstName;	// student key
	char* lastName;	// student name
	int id;		//student id
	float mark;	// course mark
};

                StudentRecord**Temp; /*Declare array of pointers to a struct*/
	Temp=new StudentRecord*[1000]; /*dynamically allocate memory*/
	Temp[0]->firstName=new char[1000]; /*crashes here, why?*/

}

[ChaosEngine]

        StudentRecord**Temp; /*Declare array of pointers to a struct*/
	Temp=new StudentRecord*[1000]; /*dynamically allocate memory*/

at this point in your code you've allocated an array of pointers. Temp[0] is a pointer, but it's not pointing to anything yet so this line

Temp[0]->firstName=new char[1000];

crashes because you are trying to access uninitialised memory.

you need to do this first.

        StudentRecord**Temp; /*Declare array of pointers to a struct*/
	Temp=new StudentRecord*[1000]; /*dynamically allocate memory*/
	Temp[0] = new StudentRecord; // allocate space for student record
	Temp[0]->firstName=new char[1000]; // should work fine now

I'm not sure why you're using an array of pointers anyway. A vector would be easier and safer or if you really need a container of pointers use a boost::ptr_vector (see my sig)

[7stud]

The pointers in the array don't point to any StudentRecord structs yet. You have to create some StudentRecord structs and assign their addresses to the pointers in the array--before you can acesss the structs.

[cmasri]

        StudentRecord**Temp; /*Declare array of pointers to a struct*/
	Temp=new StudentRecord*[1000]; /*dynamically allocate memory*/

at this point in your code you've allocated an array of pointers. Temp[0] is a pointer, but it's not pointing to anything yet so this line

Temp[0]->firstName=new char[1000];

crashes because you are trying to access uninitialised memory.

you need to do this first.

        StudentRecord**Temp; /*Declare array of pointers to a struct*/
	Temp=new StudentRecord*[1000]; /*dynamically allocate memory*/
	Temp[0] = new StudentRecord; // allocate space for student record
	Temp[0]->firstName=new char[1000]; // should work fine now

I'm not sure why you're using an array of pointers anyway. A vector would be easier and safer or if you really need a container of pointers use a boost:tr_vector (see my sig)

Thank you it works!!

[ChaosEngine]

Glad it works, but for the record this is a much more C++ way of coding

struct StudentRecord
{
	std::string firstName;	// student key
	std::string lastName;	// student name
	int id;		//student id
	float mark;	// course mark
};

std::vector<StudentRecord> Temp(1000);
Temp[0].firstName = "Chaos"

shorter and safer, and uses a lot less memory (unless you know many people with 1000 character first names! )

[cmasri]

Glad it works, but for the record this is a much more C++ way of coding

struct StudentRecord
{
	std::string firstName;	// student key
	std::string lastName;	// student name
	int id;		//student id
	float mark;	// course mark
};

std::vector<StudentRecord> Temp(1000);
Temp[0].firstName = "Chaos"

shorter and safer, and uses a lot less memory (unless you know many people with 1000 character first names! )

I don't understand this code. It is an assignment requirement to program it with array of pointers to struct. see http://ca.geocities.com/[email protected] assignment0 for your reference.

[ChaosEngine]

Ok if you have to code it like that, fair enough. And I have to say it's refreshing to see someone asking for help with a problem in a decent way rather than asking us to do their assignment for them. Keep it up.