What does m variable prefix mean

Question

I often see m  prefix used for variables  m World m Sprites      in tutorials  examples and other code mainly related to game development   Why do people add prefix m  to variables

User · Answer

Lockheed Martin uses a 3-prefix naming scheme which was wonderful to work with, especially when reading others' code.

   Scope          Reference Type(*Case-by-Case)   Type

   member   m     pointer p                       integer n
   argument a     reference r                     short   n
   local    l                                     float   f
                                                  double  f
                                                  boolean b

So...

int A::methodCall(float af_Argument1, int* apn_Arg2)
{
    lpn_Temp = apn_Arg2;
    mpf_Oops = lpn_Temp;  // Here I can see I made a mistake, I should not assign an int* to a float*
}

Take it for what's it worth.

User · Answer

As stated in the other answers  m  prefix is used to indicate that a variable is a class member  This is different from Hungarian notation because it doesn t indicate the type of the variable but its context   I use m  in C   but not in some other languages where  this  or  self  is compulsory  I don t like to see  this-   used with C   because it clutters the code   Another answer says m dsc is  bad practice  and  description   is  good practice  but this is a red herring because the problem there is the abbreviation   Another answer says typing this pops up IntelliSense but any good IDE will have a hotkey to pop up IntelliSense for the current class members

User · Answer

As stated in many other responses  m  is a prefix that denotes member variables  It is was commonly used in the C   world and propagated to other languages too  including Java    In a modern IDE it is completely redundant as the syntax highlighting makes it evident which variables are local and which ones are members  However  by the time syntax highlighting appeared in the late 90s  the convention had been around for many years and was firmly set  at least in the C   world     I do not know which tutorials you are referring to  but I will guess that they are using the convention due to one of two factors     They are C   tutorials  written by people used to the m  convention  and or    They write code in plain  monospaced  text  without syntax highlighting  so the m  convention is useful to make the examples clearer

User · Answer

One argument that I haven t seen yet is that a prefix such as m  can be used to prevent name clashing with  define d macro s   Regex search for  define  a-z  A-Za-z0-9        in  usr include term h from curses ncurses

User · Answer

To complete the current answers and as the question is not language specific  some C-project use the prefix m  to define global variables that are specific to a file -  and g  for global variables that have a scoped larger than the file they are defined  In this case global variables defined with prefix m   should be defined as static   See EDK2  a UEFI Open-Source implementation  coding convention for an example of project using this convention

User · Answer

The m  prefix is often used for member variables - I think its main advantage is that it helps create a clear distinction between a public property and the private member variable backing it   int m something  public int Something   gt  this m something     It can help to have a consistent naming convention for backing variables  and the m  prefix is one way of doing that - one that works in case-insensitive languages   How useful this is depends on the languages and the tools that you re using  Modern IDEs with strong refactor tools and intellisense have less need for conventions like this  and it s certainly not the only way of doing this  but it s worth being aware of the practice in any case

User · Answer

In Clean Code  A Handbook of Agile Software Craftsmanship there is an explicit recommendation against the usage of this prefix      You also don t need to prefix member variables with m  anymore  Your classes and functions should be small enough that you don t need them    There is also an example  C  code  of this   Bad practice   public class Part       private String m dsc     The textual description      void SetName string name                m dsc   name            Good practice   public class Part       private String description       void SetDescription string description                this description   description            We count with language constructs to refer to member variables in the case of explicitly ambiguity  i e   description member and description parameter   this

User · Answer

This is typical programming practice for defining variables that are member variables  So when you re using them later  you don t need to see where they re defined to know their scope  This is also great if you already know the scope and you re using something like intelliSense  you can start with m  and a list of all your member variables are shown  Part of Hungarian notation  see the part about scope in the examples here

User · Answer

It is common practice in C    This is because in C   you can t have same name for the member function and member variable  and getter functions are often named without  get  prefix   class Person      public        std  string name   const      private        std  string name     This would lead to a compilation error        std  string m name     OK          main cpp 9 19  error  duplicate member  name        std  string name                      main cpp 6 19  note  previous declaration is here       std  string name   const                      1 error generated        http   coliru stacked-crooked com a f38e7dbb047687ad    m   states for the  member   Prefix     is also common   You shouldn t use it in programming languages that solve this problem by using different conventions grammar

[hungarian-notation] What does `m_` variable prefix mean?

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