conversion from 'double' to 'int' requires a narrowing conversion

Question

Hi i am a c++ beginner and i really cant get my head around this error conversion from 'double' to 'int' requires a narrowing conversion this is my code; #include "Segment.h" using namespace imat1206;

Segment::Segment(int new_speed_limit
, int new_end, double new_length, double new_deceleration)
:the_speed_limit{ new_speed_limit }
, the_end{ new_end }
, the_length{ new_length }
, deceleration{ new_deceleration }


{}

Segment::Segment(double new_end, double new_acceleration)
    :the_end{ new_end }
    , acceleration{ new_acceleration }

{} error here 
double Segment::to_real() const {
return static_cast<double>((the_end)*(the_end) / (2 * (the_length)));
while (acceleration)
{
    (acceleration >= 0);
        return static_cast<double> ((the_end) /(1 * (acceleration)));
}
}

please someone help thanks
the error i am getting is : error C2397: conversion from 'double' to 'int' requires a narrowing conversion

You need to include a proper [mcve], in this case, including the .h file associated with this class. It's not clear from context where the error is occurring. — Xirema, Feb 27 '17 at 16:51

score 3 · Answer 1 · edited May 23 '17 at 10:29

The error is caused by your conversion of a double to int in the second Segment constructor. From the context of your code, I would assume that the_end is defined as an int, yet you are assigning it a double.

Segment::Segment(double new_end, double new_acceleration)
  : the_end{ new_end },               // <-- Here
    acceleration{ new_acceleration }
{

}

Your use of an initializer list in particular is causing the error as they do not allow for narrowing.

Of special note for your situation:

A floating-point value cannot be converted to an integer type.

To fix the error, simply provide an explicit cast:

Segment::Segment(double new_end, double new_acceleration)
  : the_end{ static_cast<int>(new_end) },
    acceleration{ new_acceleration }
{

}

Do note of course the potential dangers of casting from an int to a double (integer truncation, potential loss of data from going from 8 bytes to 4 bytes, etc.).

conversion from 'double' to 'int' requires a narrowing conversion

1 Answers1