newbie string question

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April 10th, 2003, 08:37 PM

maskzilla

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newbie string question

Code:

class Account{
protected:
	double acct_bal;
	unsigned acct_num;
	enum {SS_LEN = 12}; // creates class constant
	char ss[SS_LEN];

public:
	Account(){};
	Account(unsigned n, double b, char* s){
		acct_num = n;
		acct_bal = b;
		s = ss;
	};
	void deposit(double amt){
		amt += acct_bal;
	};
	int withdrawl(double amt){
	
		acct_bal -= amt;
		return 1;
	};
	double balance(){
		cout << acct_bal << endl;
		return 1;
	};
	int transfer(double amt, Account& from, Account& to){
		from.withdrawl(amt);
			to.deposit(amt);
			return 1;
		
	};
};

i just was wondering, cuz i think its wrong.. am i passing the char* s to the ss array correctly?

April 10th, 2003, 11:10 PM

Scorpions4ever

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I think you really meant to assign ss to s (instead of the other way around) in your constructor. Also, to copy strings, you should be using strcpy (or strncpy() or strlcpy() to be REALLY safe).

Code:

Account(unsigned n, double b, char* s){
		acct_num = n;
		acct_bal = b;
		strncpy(ss, s, SS_LEN);
	};

April 11th, 2003, 10:18 AM

dwise1_aol

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Quote:

Originally posted by Scorpions4ever
I think you really meant to assign ss to s (instead of the other way around) in your constructor. Also, to copy strings, you should be using strcpy (or strncpy() or strlcpy() to be REALLY safe).

Code:

Account(unsigned n, double b, char* s){ acct_num = n; acct_bal = b; strncpy(ss, s, SS_LEN); };

Or rather:

Code:

      char ss[SS_LEN+1];

     //  ...

      strncpy(ss, s, SS_LEN);
      ss[SS_LEN] = '\0';

To make room for the null terminator. And then since strncpy does not automatically include the null terminator if s is longer than SS_LEN, I normally put it at the end of the array, just in case.

Plus, you misspoke. We think he really meant to assign s to ss.

Maskzilla, the reason we want to use strcpy or strncpy is because your code was assigning a pointer to a pointer, so that ss have ended up pointing to s, rather than having copied what s was pointing to into the array pointed to by ss. If s' string was created in a function, then it would go away once you exited that function, in which case attempts to use ss would have resulted either in a segmentation fault or in clobbering other data (possibly resulting in a crash if you clobber a function's return address) or in reading a bunch of garbage.

It caused me a bit of confusion when I started learning C, but you need to get straight in your mind the difference between a character pointer and the string of characters it's pointing to, plus you need to think about what you are actually doing when you work with strings.

Last edited by dwise1_aol : April 11th, 2003 at 10:29 AM.

April 11th, 2003, 10:41 AM

Scorpions4ever

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>> To make room for the null terminator.
Yep, that's why I mentioned strlcpy() to be really safe.

>> Plus, you misspoke. We think he really meant to assign s to ss.
hehe yeah. I guess that's what happens when you're half-asleep and trying to type

newbie string question

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