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CS253 Introduction

Bjarne Stroustrup presents C++ to the Founding Fathers

Things you need to know

Do I look like your mother?

Origin

B-Strous

• 1979: Bjarne Stroustrup, at AT&T Bell Labs, began work on “C with classes”.
• 1983: “C with classes” was renamed as “C++”.
• 1998: C++ first standardized by ISO.

Dialects

• In this class, we’re learning C++, not g++.
• g++ is the particular implementation of C++ that we use in class. g++ is the compiler that transforms source code written in the C++ language into executable machine instructions.
• Many C++ compilers exist: Clang, Microsoft Visual Studio, etc.
• Similarly, there are many dialects of English, Spanish, French, etc.

Standards

auto 🐵=[](){ return "🍌"; };
cout << 🐵();

🍌

• Is that code on the right valid C++?
• How do we tell what’s real C++ and what’s a dialect?
• Let’s back up—how do know anything ?
• Definitions are by consensus. “Dog” means 🐕 because we agree on that.
• Says who? Mom? Your next-door neighbor? The President? The loudest person?
• An authority: a dictionary, the law, a committee, scholarly consensus, an influential leader, etc.

Authorities

The important part is not the answer, it’s the “according to”.

Standard C++

• C++ is defined by ISO, the International Organization for Standardization (?), and its national member organizations such as ANSI, the American National Standards Institute.
• There are several versions of the C++ standard: 1998, 2003, 2011, 2014, 2017, 2020.
• This class focuses on C++ 2017 (alias C++17).
  • It’s too soon for C++ 2020.
• I’ll let you get away with anything that g++ permits on the Linux lab computers, however.
  • g++ implements extensions to the C++ standards.
    • Handy, but dangerous. It’s easy to produce non-standard code.
  • For almost everything that you turn in, you will provide a control file (CMakeLists.txt or a Makefile) that can determine which version of C++ you want to use, via a g++ option. Specify the version that you want to use.
  • For other situations, assume C++ 2017.

Standard

An HP co-worker, Donn Terry, used to say “Standard is better than better”. This meant that doing something in the standard way is superior to doing it in a non-standard way, even if the non-standard way yields better results. True enough, as far as it goes.

If all you know is Australian English, thick with local slang, you’ll have a difficult time being understood in Detroit. Knowing Standard English can be useful.

I want you to learn standard C++. That way, your programs will work everywhere, on any standard-conforming compiler. If you use compiler extensions, non-standard features, then your program will work on that particular compiler, but perhaps not on others. Not so good.

C++ is C

When C++ was being developed, C compatibility was very important. It still is. There are zillions of C programs out there, and the creator of C++ wanted it to be very easy to take a C program and turn it into a C++ program.

Therefore, C++ is just about a superset of C. This means that almost all C programs are C++ programs.

Valid C & C++

This is a valid C program, and a valid C++ program:

#include <stdio.h>
int main() {
    printf("Hello from C!\n");
    return 0;
}

Hello from C!

#include <stdio.h>
int main() {
    printf("Hello from C++!\n");
    return 0;
}

Hello from C++!

printf() is as much a part of C++ as int and while. 97.314% of C programs are valid C++.

C++, not C

It’s the Bad Code Badger !

This is a valid C program, but not a C++ program, because C++ claimed class as a keyword:

int main() {
    int class = 253;
    printf("C: %d\n", class);
    return 0;
}

C: 253

int main() {
    int class = 253;  // 🦡
    printf("C++: %d\n", class);
    return 0;
}

c.cc:2: error: expected primary-expression before ‘int’

This is a rare exception.

Better C++

Sure, it’s better C++ style to do the first program like this:

#include <iostream>
using namespace std;
int main() {
    cout << "Hello, world!\n";
    return 0;
}

Hello, world!

However, that doesn’t change the fact that the first program is C++.

A Final Note

• Despite all that, I don’t let you use certain C facilities (printf(), malloc(), etc.) in this class.
• You must use the corresponding C++ facilities (cout, new).
• I feel no guilt about this.
• You’re too comfortable with printf(), so, if it were up to you, you’d never bother to learn cout.
• It’s like removing the training wheels from your kid’s bicycle.