When to use static keyword before global variables

Question

Can someone explain when you re supposed to use the static keyword before global variables or constants defined in header files   For example  lets say I have a header file with the line    const float kGameSpriteWidth   12 0f    Should this have static in front of const or not  What are some best practices for using static

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global static variables are initialized at compile-time unlike automatic

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You should not define global variables in header files  You should define them in  c source file    If global variable is to be visible within only one  c file  you should declare it static  If global variable is to be used across multiple  c files  you should not declare it static  Instead you should declare it extern in header file included by all  c files that need it    Example    example h  extern int global foo   foo c   include  example h   int global foo   0  static int local foo   0   int foo function           sees  global foo and local foo       cannot see  local bar        return 0     bar c   include  example h   static int local bar   0  static int local foo   0   int bar function            sees  global foo  local bar           sees also local foo  but it s not the same local foo as in foo c        it s another variable which happen to have the same name         this function cannot access local foo defined in foo c            return 0

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static renders variable local to the file which is generally a good thing  see for example this Wikipedia entry

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static before a global variable means that this variable is not accessible from outside the compilation module where it is defined   E g  imagine that you want to access a variable in another module   foo c  int var     a global variable that can be accessed from another module    static int var  means that var is local to the module only       bar c  extern int var     use the variable in foo c       Now if you declare var to be static you can t access it from anywhere but the module where foo c is compiled into   Note  that a module is the current source file  plus all included files  i e  you have to compile those files separately  then link them together

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The correct mechanism for C   in anonymous namespaces  If you want something that is local to your file  you should use an anonymous namespace rather than the static modifier

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Yes  use static  Always use static in  c files unless you need to reference the object from a different  c module   Never use static in  h files  because you will create a different object every time it is included

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The static keyword is used in C to restrict the visibility of a function or variable to its translation unit  Translation unit is the ultimate input to a C compiler from which an object file is generated   Check this  Linkage    Translation unit

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Rule of thumb for header files    declare the variable as extern int foo  and put a corresponding intialization in a single source file to get a modifiable value shared across translation units use static const int foo   42  to get a constant which can be inlined

[c] When to use static keyword before global variables?

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