[RESOLVED] Variable name

[Learned]

I have a bunch of functions sharing the variable names like:
void myfunc(int a, string b);
void func2(int c, string b);
void func3(int a, int c);

But they are not consistent in the way they have been called in functions. But I want to write a general checker for input variables. Something of sort:
if inputs are like this, then they each should have this value. E.g. 'a' should not be greater than 10, 'b' should not be less than 0, etc. I ask this cause within the function call, 'a', 'b', 'c' don't really exist per se but they contain values instead.

How do I implement this?

Thanks guys

[Skizmo]

Why not give variable names logical names instead of 1 letter-stuff. 1 letter variables are an abomination for maintaining code.

[Lindley]

One way to impose "automatic" checks on variables is to specify a unique type for the variable. For instance, "'a' should not be greater than 10" could be represented by a class IntLessThan10.

This class would need to be constructable from an int, and optionally, you could even make it implicitly convertible to an int. That way, you could use it almost exactly like an int, but it would have additional logic in the constructor which throws an exception if given an invalid argument.

[Learned]

@Lindley

Can you please elaborate some more on your suggestion, I like your idea but since I am still learning I feel I am missing quite a bit from your suggestion.

Thanks

[Paul McKenzie]

@Lindley

Can you please elaborate some more on your suggestion, I like your idea but since I am still learning I feel I am missing quite a bit from your suggestion.

Lindley described in detail as to what to do.

You need to specify exactly what you didn't understand.

Regards,

Paul McKenzie

[Learned]

This is what I have been thinking:
class lessthan10
{
public:
int a;
lessthan10() {cout<<"Bad data"; //etc.}
};

Now in the original function, if it had been:
void myfunc(int a, string b);

How would the user call it:
myfunc(1000, string b);

This would not work. Wouldn't the user need to define an object first, etc.

Thanks

[Igor Vartanov]

#include <iostream>
#include <sstream>
#include <string>
using namespace std;

class IntLessThan10
{
	int m_int;
public:
	operator int()
	{
		return m_int;
	}

	IntLessThan10(int int_): m_int(int_)
	{
		if (m_int >= 10)
			throw Exception(m_int);
	}

	struct Exception
	{
		Exception(int int_)
		{
			ostringstream str;
			str << "IntLessThan10: bad value: " << int_;
			msg = str.str();
		}
		string msg;
	};
};

void foo(IntLessThan10 a)
{
	cout << __FUNCTION__ << ": Succeeded with " << (int)a << endl;
}


int main()
{
	try
	{
		foo(-12);
		foo(7);
		foo(17);
	}
	catch(IntLessThan10::Exception e)
	{
		cout << e.msg << endl;
	}
	
	return 0;
}

D:\Temp\23>23
foo: Succeeded with -12
foo: Succeeded with 7
IntLessThan10: bad value: 17

[Learned]

Very nicely done. Thanks. I learn a lot here just reading people's code.

[Igor Vartanov]

Here's a bit more generic solution:

#include <iostream>
#include <sstream>
#include <string>
using namespace std;

struct LessThanException
{
	LessThanException(int int_, int threshold)
	{
		ostringstream str;
		str << "IntLessThan" << threshold << ": bad value: " << int_;
		msg = str.str();
	}
	string msg;
};

template <int t_threshold>
class IntLessThan
{
	int m_int;
public:
	operator int()
	{
		return m_int;
	}

	IntLessThan(int int_): m_int(int_)
	{
		if (m_int >= t_threshold)
			throw LessThanException(m_int, t_threshold);
	}
};

typedef IntLessThan<10>  IntLessThan10;

void foo(int a)
{
	IntLessThan10 dummy(a); // just check
	cout << __FUNCTION__ << ": Succeeded with " << a << endl;
}

template <int t_threshold>
void Foo(int a)
{
	IntLessThan<t_threshold> dummy(a); // just check
	cout << __FUNCTION__ << ": Succeeded with " << a << endl;
}


int main()
{
	try
	{
		foo(-12);      // threshold prefefined by foo implementation
		foo(7);
		Foo<20>(17);   // threshold explicitly specified
		Foo<15>(17);
	}
	catch(LessThanException e)
	{
		cout << e.msg << endl;
	}
	
	return 0;
}

D:\Temp\23>23.exe

foo: Succeeded with -12
foo: Succeeded with 7
Foo: Succeeded with 17
IntLessThan15: bad value: 17