Function Overloading Example Showing Error in C++

Question

I am trying to run an example of Function Overloading in C++. But Its showing me following error

        function.cpp(21): error C2084: function 'double abs(double)' already has a body
        include\math.h(495) : see previous definition of 'abs'
        function.cpp(26): error C2084: function 'long abs(long)' already has a body
        include\stdlib.h(467) : see previous definition of 'abs'

Program

#include<iostream>
using namespace std;

int abs(int i);
double abs(double d);
long abs(long l);
int main()
 {

     cout << abs(-10);
     cout << abs(-20.2);
     cout << abs(-30L);
     return 0;
 }

int abs(int i)
{
    cout << "Using int \n";
    return i<0 ? -i:i;
}

double abs(double d)
{
    cout << "Using Double \n";
    return d<0.0 ?-d:d;
}
 long abs(long l)
 {
     cout << "Using Long\n";
     return l<0?-l:l;
 }

I have copied the same code as given in book C++ Complete Reference , Fourth Edition by Herbert Schildt

You should avoid using namespace std to make sure you aren't getting one of the std::abs functions. And put your abs in a namespace to make sure you aren't getting any of the C standard library abs functions. — juanchopanza
– juanchopanza, Commented Nov 22, 2013 at 10:39
Herbert Schildt is notorius in certain quarters for writing books that describe a language that is almost but not quite the same as C++. — john
– john, Commented Nov 22, 2013 at 10:40
I removed using namespace std; line and now its showing more errors. But I am using modern compiler so it should work with using namespace std — Akash Sharma
– Akash Sharma, Commented Nov 22, 2013 at 10:42
@AkashSharma No it shouldn't. Just because using namespace std; works in one program does not mean it will work in another. You should realise (it gets said often enough) that using namespace std; is dangerous, if you don't understand the danger then you should not use it. — john
– john, Commented Nov 22, 2013 at 10:43
@AkashSharma Please describe the new errors, I would guess that you need to replace cout with std::cout. — john
– john, Commented Nov 22, 2013 at 10:43

ForEveR · Accepted Answer · 2013-11-22 11:07:19Z

9

~~You should remove using namespace std, since there is already abs function in standard-library in cmath header, or you can wrap your own functions into some namespace.~~

So, since you have errors from math.h - you should use another names of functions, or trying to wrap functions into your own namespace.

edited Nov 22, 2013 at 11:07

answered Nov 22, 2013 at 10:39

ForEveR

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7 Comments

Akash Sharma Over a year ago

I removed using namespace line and added new header <cmath> but no solution.

ForEveR Over a year ago

@AkashSharma you shouldn't include cmath. You must qualify cout with std:: prefix.

Akash Sharma Over a year ago

I tried std:: prefix but still same errors. hlinker.com/stackoverflow/errors.png

ForEveR Over a year ago

@AkashSharma ok. you should trying to wrap your functions into namespace, since there is abs in global ns.

ForEveR Over a year ago

@user2708138 it's not strange. It's not reglamented which header should be include in another header in standard library.

|

user2768863 · Accepted Answer · 2013-11-22 13:21:01Z

0

#include<iostream>
using namespace std;
int f(int d)
{   return d<0.0 ?-d:d; }
double f(double d)
{  return d<0.0 ?-d:d; }`enter code here`
int main()
 {  cout<< f(2);
   cout<< f(2.3);    
    return 0;
 }

answered Nov 22, 2013 at 13:21

user2768863

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