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Full Discussion: c++ object constructor question
Top Forums Programming c++ object constructor question Post 302433543 by vino on Wednesday 30th of June 2010 02:22:33 AM
Old 06-30-2010
Quote:
Originally Posted by santiagorf
I have the following code

Code:
class Param{
    public:
    Param(int aa, int bb){
        a=aa;
        b=bb;
    }
int a,b;
};

void function(Param);

Code:
int main(){

   function(2,3);
    return 0;
}

Code:
void function(Param par){
    cout<<par.a;
}

, and when I run it, I get the following message error:

Code:
.../main.cpp|21|error: conversion from ‘int' to non-scalar type ‘Param' requested|

I know the problem is that function should have been called with an object from Param, but I was expecting that the constructor Param(int , int) would do the job.
What is wrong with my assumption, and how could I fix this problem?

thank you in advance!!
santiagorf
This is known as implicit conversion and for constructors it works if it has a single argument only.

If you have multiple arguments and want to make use of the implicit conversion, then you need a constructor having default values.

Something like...

Code:
class Param{
public:
    Param(int a, int b = 0) : _a(a), _b(b) {}
int _a,_b;
};
void function(Param par)
{
   cout<<par.a;
}
int main(){

   function(2);
   return 0;
}

 

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LEARN ABOUT DEBIAN

mlm

FBB::mlm(3bobcat)					      OFoldStream manipulator						 FBB::mlm(3bobcat)

NAME

       FBB::mlm - Manipulator modifying left margins of OFoldStream objects

SYNOPSIS

       #include <bobcat/ofoldstream> or
       #include <bobcat/ofoldstreambuf>
       Linking option: -lbobcat

DESCRIPTION

       The  mlm  class	implements  a  manipulator that can be inserted into OFoldStream objects to modify the stream's left margin by a requested
       amount. The request cannot result in a negative left margin value. If a negative left margin would be the arithmetic result of the  request
       then left margin 0 will silently be used.

       Depending  on  the  tab-setting	of  the  OFoldStream  the  inserted value represents the number of blank space characters or the number of
       tab-characters that will be added to the left margin.

       The request will be processed at the next newline character or std::flush or std::endl manipulator that is inserted into the stream.  If  a
       line  is  still empty once an mlm object and a flush manipulator are inserted into the stream then the new left margin will be effective at
       the next word inserted into that line (cf., the example section below)

       A bad_cast exception is thrown when the manipulator is inserted into an ostream that is not using a OFoldStreambuf buffer.

NAMESPACE

       FBB
       All constructors, members, operators and manipulators, mentioned in this man-page, are defined in the namespace FBB.

INHERITS FROM

       -

CONSTRUCTOR

       o      mlm(int addValue):
	      The standard copy constructor is available.

MEMBER FUNCTIONS

       There are no public or protected member functions in this class.

EXAMPLE

	   #include <iostream>
	   #include <bobcat/ofoldstream>

	   using namespace std;
	   using namespace FBB;

	   int main()
	   {
	       OFoldStream out(cout, 0, 80);
	       out << "hello world (left margin is 0)" << mlm(4) << "
"
		      "this uses a 4 character wide left margin
" <<
		       mlm(-10) << flush <<
		       "left margin -6 changed to 0, active on this line
";
	       return 0;
	   }

FILES

       bobcat/mlm - defines the class interface

SEE ALSO

       bobcat(7), manipulators(3bobcat), lm(3bobcat), ofoldstream(3bobcat)

BUGS

       None Reported.

DISTRIBUTION FILES

       o      bobcat_3.01.00-x.dsc: detached signature;

       o      bobcat_3.01.00-x.tar.gz: source archive;

       o      bobcat_3.01.00-x_i386.changes: change log;

       o      libbobcat1_3.01.00-x_*.deb: debian package holding the libraries;

       o      libbobcat1-dev_3.01.00-x_*.deb: debian package holding the libraries, headers and manual pages;

       o      http://sourceforge.net/projects/bobcat: public archive location;

BOBCAT

       Bobcat is an acronym of `Brokken's Own Base Classes And Templates'.

COPYRIGHT

       This is free software, distributed under the terms of the GNU General Public License (GPL).

AUTHOR

       Frank B. Brokken (f.b.brokken@rug.nl).

libbobcat1-dev_3.01.00-x.tar.gz 				     2005-2012							 FBB::mlm(3bobcat)
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