dynamic memory allocation - Please help

**Space_Cowboy** · 11-13-2002

Code:

struct name{
	char user [10];
	char color [10];
}


....
....


name student[5]	// 5 students
ifstream in;
int i = 0;
in.open ("student.da");
	while (!eof){
		in.get >> student[i].user;
		in.get >> student[i].color;
		i++;
	}


I am trying to make above statements to use
dynamic memory allocation using pointers.
Since I am a newbie at this, I came up with


struct name{
	char* user;
	char* color;
}


....
....


name* student = new name[5];	// 5 students
ifstream in;
int i = 0;
in.open ("student.da");
	while (!eof){
		in.get >> student[i]->user;
		in.get >> student[i]->color;
		i++;
	}

Apparently above code is seriously ill. I don't know what I am doing wrong. Can someone please point out where?? Thanks.

Code tags added by kermi3

***kermi3*** · 11-13-2002

I am posting this because you did not use code tags on this thread. In the furture please use Code Tags. They make your code MUCH easier to read and people will be much more likely to help you if you do. And they'll be happier about helping you

For example:

Without code tags:

for(int i=0;i<5;i++)
{
cout << "No code tags are bad";
}

With Code Tags:

Code:

for(int i=0;i<5;i++)
{
     cout << "This code is easy to read";
}

This is of course a basic example...more complicated code is even easier to read with code tags than without.

I've added code tags for you this time. They can be added by putting [code] at the beginning of your code and [/code] at the end. More information on code tags may be found on the code tag post at the top of every forum. I also suggest you take a look at the board guildlines if you have not done so already.

This is a common first post mistake, just remember to use [code] tags in the future and you'll get much more help.

If this is your first time posting here the welcome, and if there's anything I can do or any questions I can answer about these forums, or anything else, please feel free and welcome to PM me.

Good Luck with your program,

Kermi3
Lead Moderator

**Eibro** · 11-13-2002

Code:

struct name{
	char* user;
	char* color;
}


name* student = new name[5];	// 5 students
ifstream in;
int i = 0;
in.open ("student.da");
	while (!eof){
		in.get >> student[i]->user;
		in.get >> student[i]->color;
		i++;
	}

First off, you need to initilize the pointers in your name structure before you can read anything in.

Before that, you need to know how much you're reading in... so we create a buffer (pszBuffer) and read UP TO 255 characters OR until a new line is found. Then we read the length of the buffer, allocate enough memory to store the characters in the buffer, and copy them to our new memory.

Code:

struct name {
char *user;
char *color;
};

// ...

name student[5];
ifstream in("student.da");
char pszBuffer[256];

int count = 0;

while (!in.eof())
{
     in.getline(pszBuffer, 255, '\n'); // read in a single line
     student[count].user = new char[strlen(pszBuffer) + 1];
     strcpy(student[count].user, pszBuffer);

     in.getline(pszBuffer, 255, '\n');
     student[count].color = new char[strlen(pszBuffer) + 1];
     strcpy(student[count].color, pszBuffer);

     count++;
}

**Space_Cowboy** · 11-13-2002

Thank you.
I will make sure I follow the guideline next time.

BTW, do you know what my problem is?

**Space_Cowboy** · 11-13-2002

Thanks Eibro!
Would you not need to initialize

name student[5];
??

Originally posted by Eibro

Code:

struct name{ char* user; char* color; } name* student = new name[5]; // 5 students ifstream in; int i = 0; in.open ("student.da"); while (!eof){ in.get >> student[i]->user; in.get >> student[i]->color; i++; }

First off, you need to initilize the pointers in your name structure before you can read anything in.

Before that, you need to know how much you're reading in... so we create a buffer (pszBuffer) and read UP TO 255 characters OR until a new line is found. Then we read the length of the buffer, allocate enough memory to store the characters in the buffer, and copy them to our new memory.

Code:

struct name { char *user; char *color; }; // ... name student[5]; ifstream in("student.da"); char pszBuffer[256]; int count = 0; while (!in.eof()) { in.getline(pszBuffer, 255, '\n'); // read in a single line student[count].user = new char[strlen(pszBuffer) + 1]; strcpy(student[count].user, pszBuffer); in.getline(pszBuffer, 255, '\n'); student[count].color = new char[strlen(pszBuffer) + 1]; strcpy(student[count].color, pszBuffer); count++; }

**Space_Cowboy** · 11-13-2002

Thanks Eibro!
Would you not need to initialize

name student[5];
??

Originally posted by Eibro

Code:

struct name{ char* user; char* color; } name* student = new name[5]; // 5 students ifstream in; int i = 0; in.open ("student.da"); while (!eof){ in.get >> student[i]->user; in.get >> student[i]->color; i++; }

First off, you need to initilize the pointers in your name structure before you can read anything in.

Before that, you need to know how much you're reading in... so we create a buffer (pszBuffer) and read UP TO 255 characters OR until a new line is found. Then we read the length of the buffer, allocate enough memory to store the characters in the buffer, and copy them to our new memory.

Code:

struct name { char *user; char *color; }; // ... name student[5]; ifstream in("student.da"); char pszBuffer[256]; int count = 0; while (!in.eof()) { in.getline(pszBuffer, 255, '\n'); // read in a single line student[count].user = new char[strlen(pszBuffer) + 1]; strcpy(student[count].user, pszBuffer); in.getline(pszBuffer, 255, '\n'); student[count].color = new char[strlen(pszBuffer) + 1]; strcpy(student[count].color, pszBuffer); count++; }

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