const vs static NSStrings in Objective-C

Question

These lines are both in the implementation file above the @implementation declaration.

NSString * const aVar = @\"aVarStringValue\";

static NSS         


        

Answer 1

In order to resolve all possible discussions on need of static and position of const:

According to C99/GNU99 specification (which usually used for Objective-C code):

• static

  • is storage-class specifier

  • objects of file level scope by default has external linkage

  • objects of file level scope with static specifier has internal linkage

• const

  • is type-qualifier (is a part of type)

  • keyword applied to immediate left instance - i.e.

    • MyObj const * myVar; - unqualified pointer to const qualified object type

    • MyObj * const myVar; - const qualified pointer to unqualified object type

  • Leftmost usage - applied to the object type, not variable

    • const MyObj * myVar; - unqualified pointer to const qualified object type

THUS:

static NSString * const myVar; - constant pointer to immutable string with internal linkage.

Absence of the static keyword will make variable name global and might lead to name conflicts within the application.