Using Singletton Pattern for global variables

[harmodrew]

Hello you all!
I read about Singletton Pattern in this post:
http://www.qtcentre.org/threads/5326...obal-variables

But if I'd like to use it to store a global variable (yes, I need it because I cannot pass it as an argument of function or other things like this) should I add only the variable in the class? as a static member?

[Lykurg]

Hi,

if you want to use the singleton patters use the last version from our wiki with the mutex locker. Then best practice is to add a local private variable and use a getter and setter function. Also a public static const default variable is useful if you store user settings with QSettings.

If you want to store a non changeable variable, i would just define a global variable without the singleton pattern.


Lykurg

[harmodrew]

and how should I declare and define a global variable? in one-file-projects you can declare a variable out of the main after the #include (it's so ugly but it's possible). for multi-file-projects where do I put global variable declaration?

[tbscope]

The most obvious things are the hardest to figure out. That's because we puny humans always think too far.

Just create a header file like mySuperDuperGlobalVariables.h
Then include the header where you need it.
Don't forget to include it once (use #ifndef, #define, ...)

[harmodrew]

Shall I add "static" to the variables so that all instances of them will edit the same phisical variable?

[Lykurg]

Just create a normal header file and include it in every file where you need that global variables. (Using namespaces is also a good choice to group your variables!)

#ifndef ARTISTICSTYLECONSTANTS_H
#define ARTISTICSTYLECONSTANTS_H
 
namespace ArtisticStyle
{
  namespace Constants
  {
    // Predefined Style Options
    const char* const ASP_STYLE     = "style";
    const int         ASP_STYLE_DEF = -1;
 
    // Tab and Bracket Options
    const char* const ASP_INDENT            = "indent";
    const bool        ASP_INDENT_DEF        = true;
    const char* const ASP_INDENTSTYLE       = "indentStyle";
    const char* const ASP_INDENTSTYLE_DEF   = "spaces";
    const char* const ASP_INDENTSIZE        = "indentSize";
    const int         ASP_INDENTSIZE_DEF    = 2;
    const char* const ASP_BRACKETS          = "brackets";
    const bool        ASP_BRACKETS_DEF      = true;
    const char* const ASP_BRACKETSSTYLE     = "bracketsStyle";
    const int         ASP_BRACKETSSTYLE_DEF = astyle::BREAK_MODE;
 
    // [...]
  }
}
 
#endif // ARTISTICSTYLECONSTANTS_H

#ifndef ARTISTICSTYLECONSTANTS_H
#define ARTISTICSTYLECONSTANTS_H

namespace ArtisticStyle
{
  namespace Constants
  {
    // Predefined Style Options
    const char* const ASP_STYLE     = "style";
    const int         ASP_STYLE_DEF = -1;

    // Tab and Bracket Options
    const char* const ASP_INDENT            = "indent";
    const bool        ASP_INDENT_DEF        = true;
    const char* const ASP_INDENTSTYLE       = "indentStyle";
    const char* const ASP_INDENTSTYLE_DEF   = "spaces";
    const char* const ASP_INDENTSIZE        = "indentSize";
    const int         ASP_INDENTSIZE_DEF    = 2;
    const char* const ASP_BRACKETS          = "brackets";
    const bool        ASP_BRACKETS_DEF      = true;
    const char* const ASP_BRACKETSSTYLE     = "bracketsStyle";
    const int         ASP_BRACKETSSTYLE_DEF = astyle::BREAK_MODE;
    
    // [...]
  }
}

#endif // ARTISTICSTYLECONSTANTS_H

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[tbscope]

static and editing very rarely go together in one sentence.
Except when pointing out that static is static and can't be edited.

static int myStaticInt = 5;
cout << "my static int =" << myStaticInt;

static int myStaticInt = 5;
cout << "my static int =" << myStaticInt;

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That's all you can do with a static variable.