C++ Overview

Posted on 2020-06-10 Edited on 2024-05-12 In Programming , Cpp

General introduction of C++ related knowledge.

Overview

What is C++

C++ is a programming language. ISO is responsible for making and maintaining its language standards.

Standards of C++

C++ 98/03, C++ 11, C++ 14, C++ 17, C++ 20

Each C++ standards consists of the

C++ features and functionalities, like lambda expression
C++ API, a collection of classes, functions and macros, also called standard library
- mainly describes the library interface and the efficiency requirement
- includes some function libraries and STL (Standard Template Library)

For more details about C++ syntax and standard library usages, refer this post.

Implementation of C++

C++ is a compiled language, meaning it needs compiler to translate into machine code, for execution or get used as a library.

Each platform implements their own compiler and standard libraries for each C++ language feature standards.

Platform (OS)	Compiler Implementation	Standard Library Implementation
Windows (x86, x64, ARM)	MSVC (Microsoft Visual C++)	MSVCRT, MinGW
Linux (x86, x64, ARM)	GCC (GNU Compiler Collection)	glibc
macOS (x86, x64, ARM)	Clang	libc++

More insights about standard libraries

Standard library is tightly coupled with Operation System because they need to convert the OS’s function into C++ interface. e.g MSVCRT needs to depend on Windows API (win32), and glibc needs to depend on Linux System Call.
In Windows platform, the compiler and standard libraries are usually aggregated into Visual Studio (IDE). But developers could also use other libraries and standard libraries implementation like MinGw. The MinGW refactors the glibc libraries by replacing Linux System Call with Windows API.

Therefore, a C++ project needs to set the target platform and the language standard version, then uses respective compiler to compile and depends on respective standard libraries.

Compile Link Process

C++ uses the compile link model to convert source code to binary machine code for execution. The compile process requires lots of resources but the number of input files are usually small. The link process has lots of files input but the processing speed is fast.

Preprocess: interpret the macro, convert source code to “interpret unit” (source code + related header files - preprocess commands)
- e.g. interpret #pragma once
Compile: convert interpret unit to object files
- Cpp Compiler: convert to assembly code
- Assembler: covert to binary file
Link: combine with other library files

Clang compile process

Different compiler has their own compiling process. Clang in macOS use a 3-steps process and uses the LLVM (Low-Level Virtual Machine) as the compile backend.

Clang separate the compile process into

Frontend: analyze syntax of source code, generate IR (Intermediate Representation)
Optimizer: optimize IR code
Backend: convert IR into machine code according to specific OS architecture

Strengths

High performance
- Stay closely with underline hardware: different platforms may have different results
- Control the lifecycle of the object accurately
- Zero-overhead abstraction
  - Don’t need to pay for unused features e.g. virtual function tables won’t be generated for classes don’t used virtual functions
  - Don’t need to pay during runtime for some language features
For large projects
- Process oriented, object oriented, generics oriented
- Function override, exception handling, reference type

Dialects

Dialects is the standard C++ with some extensions.

Name	Description
C++/CLI	- extension of the C++ - includes new keywords such as the `ref new` and `^` (hat) notation
C++/CX	- adds non-standard extensions to the C++ language - inherited syntax from C++/CLI

Library

Library is a collection of non-volatile resources used by computer programs. These may include configuration data, documentation, help data, message templates, pre-written code and subroutines, classes, values or type specifications. A library is also a collection of implementations of behavior, written in terms of a language, that has a well-defined interface by which the behavior is invoked.

WRL (Windows Runtime C++ Template Library, Legacy). WRL is exception-free, meaning its return-value discipline is HRESULT-based just like that of COM.

C++/WinRT is an entirely standard C++ language projection (the way that Win32 uses to present APIs) for Microsoft’s Windows Runtime (WinRT) platform, designed to provide access to modern Windows APIs, implemented as a header-file-based library. With C++/WinRT, developers can author and consume Windows Runtime APIs using any standards-compliant C++17 compiler. Github link

C++/WinRT is standard C++, so we cannot use it to determine the application type. Both Win32 applications and UWP applications are able to use C++/WinRT to call WinRT APIs.

Boost library is also a famous library for C++, which is usually regarded as a pre-standard library.

Build System

When the C++ project is too large so using compiler directly is not convenient, build system needs to be used.

Some common-used build systems include

Make: GNU build tool. Used Makefile to execute the building process.
ninja: build system focusing on build efficiency, especially when doing incremental build. Using build.ninja

Both Makefile and build.ninja files are hard to write directly, so build system generator like CMake, which uses human-friendly CMakeList.txt, needs to be used to generate them.

Therefore, the whole building process for a large C++ project are as follows.

Write CMakeList.txt files with CMake syntax to configure the projects
Use CMake to generate Makefile or build.ninja files
- Could specify which one to use like cmake -G ninja
Use Make or ninja to build the files using different compilers

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