Thread: Assert: When to and when not to.

I would go with something like

Code:

if ( _employee != NULL ) {
    // do stuff
} else {
    assert(_employee != NULL);
}

This way, the code won't suddenly blow up in a release build should a NULL pointer unexpectedly arrive.

I could carp about symbols beginning with underscore as well.

Originally Posted by Salem

I would go with something like

Code:

if ( _employee != NULL ) {
    // do stuff
} else {
    assert(_employee != NULL);
}

This way, the code won't suddenly blow up in a release build should a NULL pointer unexpectedly arrive.

I could carp about symbols beginning with underscore as well.

That's just my way to differentiate between local variables and passed variables, any other suggestions for that?

Originally Posted by Shamino

That's just my way to differentiate between local variables and passed variables, any other suggestions for that?

Add the "_" at the end of the variable name instead.
Leading underscores on variable names tend to be reserved for compiler and library users.

Tim S.

I've made some adjustments according to the responses to the thread, thanks for your input everyone!

Employee.h:

Code:

#ifndef EMPLOYEE_H
#define EMPLOYEE_H
#include <string>
using namespace std;

class employee
{
public:
	employee(string _name, string _payrate)
	{
		name = _name;
		payrate = _payrate;
	}

	string& get_name()
	{
		return name;
	}

	string& get_payrate()
	{
		return payrate;
	}
	void edit()
	{
		string input;
		int selection;
		bool goodinput = false;		//loop conditional, input must match conditions, else continue
		while (goodinput == false)
		{
			cout << "What would you like to change?" << endl		// prompt
				 << "1. Name" << endl << "2. Payrate" << endl;

			getline(cin, input);	//get input
			stringstream(input) >> selection;	//extract selection integer

			if (selection == 1)
			{
				cout << "Please enter a name for this employee: ";
				getline(cin, name);
				goodinput = true;
			}
			else if (selection == 2)
			{
				goodinput = true;
				cout << "Please enter a pay rate for this employee (hourly): ";
				getline(cin, payrate);	
			}
			else
			{
				goodinput = false;	// invalid selection - continue loop
				cout << "Please enter a valid selection, 1 or 2." << endl;
			}
		}
	}

private:
	string name;
	string payrate;
};

#endif

Experimentations.cpp (main)

Code:

// Experimentations.cpp : main project file.

#include "stdafx.h"
#include <iostream>
#include <string>
#include <sstream>
#include <vector>
#include <assert.h>
#include "Employee.h"
using namespace std;

vector<employee> employees;

employee create()
{
    cout << "Please enter the new employee's name: ";
    string name;
    getline(cin, name);
    cout << "Please enter the new employee's payrate: ";
    string payrate;
    getline(cin, payrate);
    employee new_employee(name, payrate);
	return new_employee;
}

employee & get_employee(string name)
{
	for (unsigned int i = 0; i < employees.size();)
	{
		if (name.compare(employees[i].get_name()) == 1)
		{
			return employees[i];
		}
		else
		{
			i++;
		}
	}
	throw;
}

void list_employees(vector<employee> & employees)
{
	for (unsigned int i = 0; i < employees.size(); i++)
	{
		cout << employees[i].get_name() << endl;
	}
}

int main()
{
	int selection;
	string input;
	bool goodinput = false;
    while (goodinput == false)
	{
		cout << "Welcome to the employee database, what would you like to do?" << endl		// prompt
			 << "1. Add an employee" << endl << "2. Modify an employee" << endl;

		getline(cin, input);	//get input
		stringstream(input) >> selection;	//extract selection integer

		if (selection == 1)
		{
			goodinput = true;
			employees.push_back(create());
		}
		else if (selection == 2)
		{
			cout << "Enter the name of the employee you'd like to edit: ";
			getline(cin, input);
			get_employee(input).edit();
			goodinput = true;
		}
		else
		{
			goodinput = false;	// invalid selection - continue loop
			cout << "Please enter a valid selection, 1 or 2." << endl;
		}
	}
    return 0;
}

I'm not quite sure how to logically arrange the functions that actually handle the employees vector. I'm thinking about making menu objects to simplify that aspect of programming this thing, any suggestions?

Originally Posted by Salem

I would go with something like

Code:

if ( _employee != NULL ) {
    // do stuff
} else {
    assert(_employee != NULL);
}

This way, the code won't suddenly blow up in a release build should a NULL pointer unexpectedly arrive.

That's one of those "This should never happen, but if it does" kind of things. Those bug me because it really shows that the programmer is unsure if putting the assert there is the right thing to do, i.e. they aren't sure if it will never happen. If you're sure enough that it can't happen to go and put the assert there, then why on earth would you code for the possibility that you were wrong? It just means you were never sure enough to put the assert there to begin with.

Precondition testing is basically one of the reasons that you can never be sure that an assert is appropriate, and in that case it is fair enough.
One option is throwing on error:

Code:

if (employee == NULL) throw something;

However to avoid such an exception from being inadvertantly caught and ignored, you unfortunately do need to assert also. At work we use an ASSERT_THEN_THROW_IF_FALSE macro. Yes its long and wordy, but I don't have to explain what it does now do I

Something allong the lines of a CHECK_PRECONDITION macro might be even better.

Then you can save the assert for things which you know for sure are not going to be false.