Thread: about return value

There is no universal solution, but there are many options. Look up the different ways that a function can return data to the caller. You'll learn better if you hunt for the information yourself (it is not that hard to find in basic introductory texts) rather than being spoonfed.

"Bitflags" are pretty popular, you have perhaps had to use them even if you haven't implemented them yourself:

Code:

#include <iostream>
#include <string>

#define OK	0
#define TOO_SHORT 1
#define INVALID_CHAR 2
#define NO_CAP 4

using namespace std;

int validate_password (const string &pw) {
	int rv = OK, i, cap = 0, len = pw.length();
	if (len < 8) rv |= TOO_SHORT;
	for (i = 0; i < len; i++) {
		if (pw[i] < '0' || (pw[i] > '9' && pw[i] < 'A')
		  || (pw[i] > 'Z' && pw[i] < 'a') || pw[i] > 'z') {
			rv |= INVALID_CHAR;
			continue;
		}
		if (pw[i] >= 'A' && pw[i] <= 'Z') cap++;
	}
	if (!cap) rv |= NO_CAP;
	return rv;
}

int main(int argc, const char *argv[]) {
	string eg;
	cout << "Enter password: ";
	cin >> eg;

	int err = validate_password(eg);
	cout << "Validating \"" << eg << "\"...\n";
	if (err) {
		if (err & TOO_SHORT) cout << "Password must be 8+ characters.\n";
		if (err & INVALID_CHAR) cout << "Password must be only alphanumeric characters.\n";
		if (err & NO_CAP) cout << "Password must contain a capital letter\n";
	} else cout << "All good!\n";

	return 0;
}

Notice that the values of the flags are exponential -- 1, 2, 4 -- and not sequential -- 1, 2, 3. If you don't know why that is, you should, so ask. Anyway, a single int using bitflags can be used to return upto 32 (1 per bit) different possibilities alone, and in combination:

Code:

[root~/C++] ./a.out
Enter password: asdf1234
Validating "asdf1234"...
Password must contain a capital letter
[root~/C++] ./a.out
Enter password: g56$
Validating "g56$"...
Password must be 8+ characters.
Password must be only alphanumeric characters.
Password must contain a capital letter

Originally Posted by threahdead

wrong thread?

In what sense? The OP's question:

Originally Posted by talentspsp

if a function needs to return a value to indicate MULTIPLE status, such like success and different situations of failure(more than one, so can't return bool), what value should be returned

Using bitflags to do that is certainly very common.

Maybe this was left implicit, but a value of OK (zero) cannot contain any flags, because 0 == no bits set. So returning 0 indicates success, anything else indicates an error, and then you AND test the int to see which error states are set:

Code:

	if (err) {
		if (err & TOO_SHORT) cout << "Password must be 8+ characters.\n";
		if (err & INVALID_CHAR) cout << "Password must be only alphanumeric characters.\n";
		if (err & NO_CAP) cout << "Password must contain a capital letter\n";
	} else cout << "All good!\n";

So that single int can contain multiple states -- it can be TOO_SHORT and also INVALID_CHAR, or it could just be one or the other. In the example, these all pertain to one thing, but they could pertain to completely different things. The point being, it's all contained in a single return value.

Of course, you don't have to use the zero to indicate success. If you have a non-zero flag(s) for success, then you can return success and also indicate the kind of success:

Code:

#define SUCCESS_A 8
#define SUCCESS_B 16

You can make "flags" an int field in a struct too, also very common. Again, if anyone does not understand the nature of logical AND(&, different from &&, the "and" operator), logical OR (|, different from ||, the "or" operator) and bit ops generally, just ask or google "bitflags", "bitmask" or "bit operations". They are certainly the most efficient way to do something like this and also a programming fundamental everyone should understand.

Bitflags/bitmasks (same thing) are also used to set multiple possibilities. For example, the second parameter to ofstream is a bitmask:

Code:

ofstream ("somefile", ios_base::out | ios_base::binary | ios_base::trunc);

Opens a binary file for writing, and truncates it's length to zero. The parameter is type ios_base :: openmode which is an unsigned int.

Code:

#define OK	0
#define TOO_SHORT 1
#define INVALID_CHAR 2
#define NO_CAP 4

Those defines really should be constants:

Code:

const int OK = 0;
const int TOO_SHORT = 1;
const int INVALID_CHAR = 2;
const int NO_CAP = 4;