Modern C++ - Basics

1. Basics

The C++ programming language

C++ (/ˈsiː plʌs plʌs/) is a general-purpose programming language. It has imperative, object-oriented and generic programming features, while also providing facilities for low-level memory manipulation.

(from wikipedia

History of C++

Origins

Assembly -> BCPL -> B -> C          -> D
                             -> C++ -> Java
          Algol -> Algol68          -> C#
        Fortran -> Simula67

Timeline

• 1980 Bjarne Stroustrup starts working on C with Classes
• 1983 The new language is named as C++
• 1985 Aleksey Stepanov works on Generic programming
• 1990 The language has exceptions
• 1990 The Annotated Reference Manual (ARM) (book from Stroustrup and M. Ellis)
• 1991 ISO standardisation process starts
• 1994 The Design and Evolution of C++ (book from Stroustrup)
• 1998 C++ standard ISO/IEC 14882:1998
• 2003 Minor bugfixes (C++03 standard)
• 2011 Major language revision (C++11 standard)
• 2014 Minor revision (C++14)
• 2017 Major language revision (C++17)

Design goals of C++

Type safety

C++ is a statically, strongly typed programming language The compiler decides the type of all (sub)expression in compile time

In run time: pointers, conversions, Object-oriented constructs brings dynamism into the static type system.

Resource safety

• Not just memory! All resources (files, sockets, locks, etc.)
• No garbage collection by def. (but can implement)
• Use the RAII (Resource Acquisition Is Initialization) idiom

Many beginner makes resource errors.

Performance

• Direct access to HW resources. No virtual machine
• High performance trading, phone exchange systems
• Low energy cosumption (Mars rover)

C++ programs does not guarantees high performance! They gives control to the programmer to decide on performance-related issues.

Predictability

Orthogonal features should work well together. Capability to safety implement large systems (2-10 million eLoC).

Learnability, readability

Lots of problems in earlier versions. C++11 version goes from expert-friendly to novice-friendly.

Compiling, linking

  preprocessing   compiling         linking   executing

header      source      object       library

  a.h
  b.h   ->    b.c    ->   b.o  ---------|
                                        ----->    a.out (b.exe)
  e.h                                   |            |
  f.h   ->    d.c    ->   d.o  ---------|            |runtime
                                        |            |
  g.h   ->    g.c    ->   g.o           |            |
  h.h   ->    h.c    ->   h.o    ->   h.a  (h.lib)   |
                                       archive       |
  i.h   ->    i.c    ->   i.o                        |
  j.h   ->    j.c    ->   j.o    ->   j.so (j.dll) --|
                                      shared object

First C++ program: hello world

$ cat hello.cpp

1 #include <iostream>
2 
3 int main()
4 {
5   std::cout << "hello world" << std::endl;
6   return 0;
7 }

Compiling, linking, executing

# compile + link
$ g++  hello.cpp

# execute
$ ./a.out
hello world

# compile + link + set warnings on
$ g++ -ansi -pedantic -Wall -W hello.cpp

# c++11 mode
$ g++ -std=c++11 -ansi -pedantic -Wall hello.cpp

# set output name to hello.exe
$ g++ -std=c++11 -ansi -pedantic -Wall hello.cpp -o hello.exe

# compile only
$ g++ -c  hello.cpp
$ ls
hello.o

# will call the linker 
$ g++ hello.o
$ ls
a.out

# calls the compiler for all sources then calls the linker
$ g++ a.cpp b.cpp d.o e.a f.so

Compiler errors, warnings

If we make a syntax error, the compiler emits error(s):

 1 /*
 2  *  BAD VERSION !!!
 3  *  Missing semicolon
 4  */
 5 #include <iostream>
 6 
 7 int main()
 8 {
 9   std::cout << "hello world" << std::endl // missing ;
10   return 0;
11 }

$ g++ -ansi -pedantic -W -Wall hello.cpp 
hello.cpp: In function ‘int main()’:
hello.cpp:10:3: error: expected ‘;’ before ‘return’
   return 0;
   ^

If there is a syntax error, do compiler do not generate object code. When we have a warning, the compiler does generate object output.

1 #include <iostream>
2 
3 int main()
4 {
5   int i = 1;
6   return 0;
7 }

g++ -ansi -pedantic -Wall -W unused.cpp 
unused.cpp: In function ‘int main()’:
unused.cpp:9:7: warning: unused variable ‘i’ [-Wunused-variable]
   int i = 1;
       ^

Warnings can be serious things in C++, you should treat them as errors unless you are absolute sure in the opposite. Even there, it is a good habit to write warning-free code.