Question:

What are C++ inline functions?

Answer:

C++ inline functions are special functions, for which the compiler replaces the function call with body/definition of function. Inline functions makes the program execute faster than the normal functions, since the overhead involved in saving current state to stack on the function call is avoided. By giving developer the control of making a function as inline, he can further optimize the code based on application logic. But actually, it's the compiler that decides whether to make a function inline or not regardless of it's declaration. Compiler may choose to make a non inline function inline and vice versa. Declaring a function as inline is in effect a request to the compiler to make it inline, which compiler may ignore. So, please note this point for the interview that, it is upto the compiler to make a function inline or not.

inline int min(int a, int b)
{
   return (a < b)? a : b;
}
 
int main( )
{
   cout << "min (20,10): " << min(20,10) << endl;
   cout << "min (0,200): " << min(0,200) << endl;
   cout << "min (100,1010): " << min(100,1010) << endl;
   return 0;
}

If the complier decides to make the function min as inline, then the above code will internally look as if it was written like

int main( )
{
   cout << "min (20,10): " << ((20 < 10)? 20 : 10) << endl;
   cout << "min (0,200): " << ((0 < 200)? 0 : 200) << endl;
   cout << "min (100,1010): " << ((100 < 1010)? 100 : 1010) << endl;
   return 0;
}

 


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