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CppScope

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(C++) Scope

The scope of a variable is the area where its name is valid. A variable declared inside a function is only valid inside that function. Thus its scope is inside the function (from Doctor Slush, Scope).

In C++, a scope is defined by accolades.

include <iostream>

int main()
{
  int a = 0;
  {
    int b = 0;
  } //b goes out of scope
  
  for (int i=0; i<10; ++i) std::cout << "Hello world" << std::endl; }
}

A variable 'without scope' is called a global variable. When the compiler needs to choose between a global and local variable, it will choose the local.

include <iostream>

include <cassert>


int a = 10; //Global 'a'
int main()
{
  int a = 0; //Local 'a'
  assert(a==0);
  assert(::a==10); //Use scope operator to get global 'a'
}

Keep scopes small [1]. Don't use the same name in both a scope and an enclosing scope [2].

Topic links

• #include
• scope operator'::'
• stream out operator '<<'
• assert
• cout
• endl
• for
• #include
• int
• iostream
• main
• return
• scope operator'::'
• std
• stream out operator '<<'

Reference

• 1) Bjarne Stroustrup. The C++ Programming Language (3rd edition).ISBN: 0-201-88954-4. item 4.10.1: 'Keep scopes small'.
• 2) Bjarne Stroustrup. The C++ Programming Language (3rd edition).ISBN: 0-201-88954-4. item 4.10.2: 'Don't use the same name in both a scope and an enclosing scope'.

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