小编pet*_*kun的帖子

在我的Gemfile中,我指定了:

ruby '1.9.3', engine: 'jruby', engine_version: '1.7.9'

但进入我的Rails项目目录会rvm引发此错误:

RVM used your Gemfile for selecting Ruby, it is all fine - Heroku does that too,
you can ignore these warnings with 'rvm rvmrc warning ignore /home/petey/rails/kotoba/Gemfile'.
To ignore the warning for all files run 'rvm rvmrc warning ignore allGemfiles'.

ruby-1.9.3,engine:jruby,engine_version:1.7.9 is not installed.
To install do: 'rvm install ruby-1.9.3,engine:jruby,engine_version:1.7.9'

但是,我确实安装了jruby 1.7.9:

$ rvm list

rvm rubies

   jruby-1.7.9 [ x86_64 ]
   ruby-1.9.3-p392 [ x86_64 ]
=* ruby-2.0.0-p247 [ x86_64 ] …

所以,我已经为obj1 + obj2进行了类内运算符重载:

fraction operator+ (fraction op);

类似地,cout << obj正在通过重载运算符重载ostream来工作:

ostream& operator<< (ostream& os, fraction& frac);

但是,如果我试图将两者结合起来,那么一切都会破裂.

fraction.cpp:77:27: error: no match for ‘operator<<’ in 
‘std::operator<< [with _Traits = std::char_traits<char>]((* & std::cout), ((const char*)"Sum: ")) 
<< f1.fraction::operator+(f2)’

这是代码:

#include <iostream>
using namespace std;

class fraction
{
    private:
        int n, d;

    public:
        fraction ()
        {
            this->n = 1;
            this->d = 0;
        }

        fraction (int n, int d)
        {
            this->n = n;
            this->d = d;
        }

        int getNumerator ()
        {
            return n;
        } …