Language Keywords

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// const keyword use case in cpp

const int Constant1 = 96; // an integer constant
    
const int * Constant2 // Constant2 is a variable pointer to a constant integer
int const * Constant2 // same as above
    
int * const Constant3 // Constant3 is constant pointer to a variable integer
    
int const * const Constant4 // Constant4 is constant pointer to a constant integer
    
// Basically ‘const’ applies to whatever is on its immediate left 
// (other than if there is nothing there in which case it applies 
// to whatever is its immediate right).

const char *Function1() { return "Some text"; } // the return value of Function1 is unalterable

void Subroutine4(big_structure_type const &Parameter1); // the variable is passed without copying and is unalterable

class Class2
{
  void Method1() const; // Method1 cannot alter any member variables in the object
  int MemberVariable1;
}

const int*const Method3(const int*const&)const;
// a const member function named Method3 that 
// takes a reference to a const pointer to an int const (or a const int) and 
// returns a const pointer to an int const (const int)

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explicit class_name ( params ) // specifies that this constructor is only considered for direct initialization (including explicit conversions)
explicit operator type ( ) // specifies that this user-defined conversion function is only considered for direct initialization (including explicit conversions)

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// share a variable between a few modules.
// define it in one module, 
// and use extern in the others.

// file1.cpp:
int global_int = 1;

// file2.cpp:
extern int global_int;
cout << "global_int = " << global_int;