- In some programming languages, it is
not possible to define
two (or more) (different) functions
that has the
same name
Example:
void f(int i) { printf("i = %d\n\n", i); } void f(double f) { printf("f = %f\n\n", f); }
- This is
illegal
in
non-object oriented programming languages such as
C .
- Example C Program:
(Demo above code)
- Prog file: click here
Compile this program with "cc overload01.c"
Result:
line 10: identifier redefined: f current : function(double) returning void previous: function(int) returning void : "overload01.c", line 4
- Object oriented programming languages,
such as
the C++ and Java programming language
do allow
multiple functions with the
same name
- Example Program:
(Demo above code)
- Prog file: click here
Compile this program with "CC overload02.C" and run it...
- C++ can even tell the
difference
between
float
and
double:
void f(float f) { cout << "float f = " << f << endl << endl; } void f(double d) { cout << "double d = " << d << endl << endl; }
int main(int argc, char *argv[]) { float y = 4.0; double z = 4.0; f(y); f(z); f(3.0); // A constant is always "int" or "double" f((float) 3.0); // force "float" } - Example Program:
(Demo above code)
- Prog file: click here
- We say that a function name is overloaded when there are different functions with the same name
- C
identifies
a function
using
only the function name
- In contrast,
C++
identifies
a function
using
its function name
and
the number and type of its parameters
Example:
int i; double f; f(i); // will invoke f(int) f(f); // will invoke f(double) f(3); // will invoke f(int) f(3.0); // will invoke f(double) f((float) 3.0); // will invoke f(float)
- Overloading functions is a great feature to
implement the
same operation
on
different type of data.
- Example:
matrix-matrix
multiplication
and
matrix-vector
multiplication
class Matrix3 { public: float A[3][3]; }; class Vector3 { public: float x[3]; };// ============================ Matrix-matrix multiply Matrix3 operator*(Matrix3 & M1, Matrix3 & M2) { Matrix3 r; int i, j, k; for (i = 0; i < 3; i=i+1) for (j = 0; j < 3; j=j+1) r.A[i][j] = 0; for (i = 0; i < 3; i=i+1) for (j = 0; j < 3; j=j+1) for (k = 0; k < 3; k=k+1) r.A[i][j] = r.A[i][j] + M1.A[i][k]*M2.A[k][j]; return r; } // ============================ Matrix-vector multiply Vector3 operator*(Matrix3 &M, Vector3 &v) { Vector3 z; int i, j; for (i = 0; i < 3; i=i+1) z.x[i] = 0; for (i = 0; i < 3; i=i+1) for (j = 0; j < 3; j=j+1) z.x[i] = z.x[i] + M.A[i][j]*v.x[j]; return z; }int main(int argc, char *argv[]) { Matrix3 M1, M2, M3; Vector3 v1, v2; M3 = M1 * M2; // Selects Matrix-matrix multiply // because operator*(Matrix3,Matrix3) v2 = M2 * v1; // Select Matrix-vector multiply // because operator*(Matrix3,Vector3) } - Example Program:
(Demo above code)
- Prog file: click here