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Function

Posted By: Ryan Evans     Category: C++ Programming     Views: 4587

This article explains about functions in c++.

Return From The Function

  • In C++ main returns type int to OS
  • The function prototyping is essential here
  • Prototyping requires each variable to be declared separately while variable names can be omitted
  • Function() is same as function(void) in c++
  • Void do_something(…) is possible to have 
  • In C++ use of void is redundant and unnecessary
  • Call by reference is by reference variables
  • Return by reference is also possible

Return by Reference Example

 int & max(int & x, int & y)
 {
     if (x>y)
             return x;
     else 
             return y;
  }

max(a,b) = -1 is then legal and assigns the value   -1 larger of a and b

Inline Request to Compiler

  • The context switching problem for small functions and inappropriateness of macro
  • The inline function definition
  • The inline request may not be accepted when
    • For function returning values  if loop, switch or goto exists
    • For functions not returning values, if a return statement exists
    • Functions either containing static variables 
    • Function is recursive 


Default Arguments

 float amt(float prin, int period, float rate = 1.5);
 value = amount ( 5000,5); // third arg missing 
 value = amount ( 5000,5,1.7); //no missing arg

A default argument is checked for type at the time of declaration and evaluated at the time of call
Only the trailing args can be default args

 int mul(int i, int j = 5,int k = 6) // valid
 int mul(int i = 5, int j) //invalid
 int mul(int i = 0, int j, int k =10) // invalid
 int mul(int i = 2, int j = 0, int k =10)// valid

Const Args and Function Overloading

 int strlen(const char *p);
 int length (const string & s);
 int add(int a, int b)
 int add(int a, int b, int c)
 double add(double x, double y)
 double add(int p, double q)
 double add(double p, int q)

Argument Matching

  • Here compiler tries to get an exact match 
  • Otherwise compiler uses the integral promotion like char to int, float to double
  • Otherwise it tries to use built in conversion
  • At the time of conversion, if more matches are found, compiler will generate an error
  • If all of the steps fail, compiler will try to use user defined conversions in combination with integral promotions and built in conversions
  
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Ryan Evans
Ryan Evans author of Function is from London, United Kingdom.
 
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