sysprog_needs_to_know.txt

WHAT A SYSTEM PROGRAMMER NEEDS TO KNOW

(Notes for oneself and the addendum for THE C++ CODE REVIEWER NOTES https://github.com/kuzminrobin/first_step_on_github/blob/master/cpp_code_reviewer_notes.txt)

Contents.
=========
[VLA] Variable Length Array.


[VLA]
What a system programmer needs to know about 
Variable Length Array.
=======================
Conclusion: 
-----------
Variable Length Array is a C language feature (starting with C99) but not a C++ language feature (as of C++14).

What the Variable Length Array is.
----------------------------------
It is stack-allocated array whose length is a run-time value. E.g.
    void func(char *pc)
    {
       char arr[strlen(pc)]; // The length of `arr` is a run-time value.
    }
The Variable Length Arrays, since they are stack-allocated, are more efficient than the heap-allocated arrays.

Recommendations:
----------------
If you need to use the Variable Length Arrays in C++ code (and want the code to be portable and warningless) then consider placing the code (using the Variable Length Array) in the `.c` files and compiling using the C (not C++) compiler. E.g.
VLA_code.h
    void func(char *pc);    // Declaration in C header.

VLA_code.c
    void func(char *pc)     // Definition in C file.
    {
       char arr[strlen(pc)]; // The length of `arr` is a run-time value.
       . . .
    }

VLA_user.cpp
    extern "C" {            // Use C language linkage in C++ code.
    #include "VLA_code.h"
    }
    . . .
    func("Hello, World!");  // Call to C function from C++ code.
    
What the Variable Length Array is, Standard Citation: 
-----------------------------------------------------
C99, 6.7.5.2 Array declarators, paragraph 4:
If the size is an integer constant expression and the element type has a known constant size, the array type is not a variable length array type; otherwise, the array type is a variable length array type.

Compiler warnings/errors (https://godbolt.org):
-----------------------------------------------
  Comipler options: -Wextra -pedantic -std=c++03
    [ARM gcc 4.6.4 (linux) #1] warning: ISO C++ forbids variable length array 'array' [-Wvla].
    [x86-64 clang 5.0.0 #1] warning: variable length arrays are a C99 feature [-Wvla-extension].
  No compiler options:
    [x86 MSVC 19 2017 RTW #1] error C2131: expression did not evaluate to a constant

Standard Provisions:
--------------------
C99 (ISO/IEC 9899:1999 (E)): Search for "variable length array", "variable-length array", "VLA".
C?? (Latest, TODO).
C++03 (ISO/IEC 14882:2003(E)): ?
C++14/17 (TODO)


TODO:
=====
Terms
    System Programming
Non-lang Specific
  const
  When to use asserts (see also Before Writing Asserts)
C++
  Logging
    Alexandrescu article.
  Before Writing Singleton Design Pattern
  Before Writing Smart Pointers
  Before Writing Asserts
  Type-Safe Programming
    Jonathan Muller
    Non-Ignorable Return Value
  New Features in a Specific Edition of the C++ Standard
    Anthony Calandra
Other Langs
  Advantages of C over C++
    [VLA]
    Struct initializer (struct { char c; int i; } s = { .c = 2, .i = 1 };)
  Advantages of D over C++
      How Nested Functions Can Help To Avoid `goto`
  Advantages of Rust over C++

How to Accelerate 
  GIT Cloning
    Shallow Clones
    Symlink to a local GIT repo (.git) - Single Full Repo, Multiple Working Dirs.
  The Build
    ccache
    Building on a RAM Drive
    SSD Drive

People
    Where a Person Known in System Programming World Can Be Met
        Walter Bright (the designer of the D programming language)
        
Chronological List of System Programming Books