What library is the error() function in?

Question

I try to use the error() function in my program, but it shows "Error: identifier "error" is undefined". Is there a library that I need to include? This is found from a book called "Programming Principles and Practice Using C++". The error() function will terminate the program with a system error message plus the string that is passed to error() as an argument.

if (x<=0) error("non-positive x"); 
if (y<=0) error("non-positive y");
int area1 = area(x,y); 

Really, the only question is what to do if we find an error. Here, we have called a function error() which we assume will do something sensible. In fact, in std_lib_facilities.h we supply an error() function that by default terminates the program with a system error message plus the string we passed as an argument to error(). If you prefer to write out your own error message or take other actions, you catch runtime_error (§5.6.2, §7.3, §7.8, §B.2.1). This approach suffices for most student programs and is an example of a style that can be used for more sophisticated error handling.

Answer 1

It is a user defined function. If you take a look at section 5.6.3 "Bad input", you can see, he defines it as:

void error (string s)

{
  throw runtime_error (s);
}

He redefines it further in the text to accept two arguments.

Answer 2

In your book

Support

The book's support website, http://www.stroustrup.com/Programming, contains a variety of materials supporting the teaching and learning of programming using this book. The material is likely to be improved with time, but for starters, you can find:

• Slides for lectures based on the book
• An instructor's guide
• Header flies and implementations of libraries used in the book
• Code for examples in the book
• Solutions to selected exercises
• Potentially useful links
• Errata Suggestions for improvements are always welcome.

And later at the end of first chapter:

So, here is your first drill:

1. Go to Appendix C and follow the steps required to set up a project. Set up an empty, console C++ project called hello_ world.

[...]

How do you find std_lib_facilities.h? If you are in a course, ask your instructor. If not, download it from our support site http://www.stroustrup.com/Programming.