How to read-write into/from text file with comma separated values

by

Step 1:
Don’t do this:

while(!file.eof())
{
    getline(file,line);
    numlines++;
}
numline--;

The EOF is not true until you try and read past it.
The standard pattern is:

while(getline(file,line))
{
    ++numline;
}

Also note that std::getline() can optionally take a third parameter. This is the character to break on. By default this is the line terminator but you can specify a comma.

while(getline(file,line))
{
    std::stringstream   linestream(line);
    std::string         value;

    while(getline(linestream,value,','))
    {
        std::cout << "Value(" << value << ")\n";
    }
    std::cout << "Line Finished" << std::endl;

}

If you store all the values in a single vector then print them out using a fixed width. Then I would do something like this.

struct LineWriter
{
        LineWriter(std::ostream& str,int size)
                :m_str(str)
                ,m_size(size)
                ,m_current(0)
        {}

        // The std::copy() does assignement to an iterator.
        // This looks like this  (*result) = <value>;
        // So overide the operator * and the operator = to
        LineWriter& operator*() {return *this;}   
        void operator=(int val)
        {
                ++m_current;
                m_str << val << (((m_current % m_size) == 0)?"\n":",");
        }

        // std::copy() increments the iterator. But this is not usfull here
        // so just implement too empty methods to handle the increment.
        void operator++()       {}
        void operator++(int)    {}

        // Local data.
        std::ostream&           m_str;
        int const               m_size;
        int                     m_current;
};

void printCommaSepFixedSizeLinesFromVector(std::vector const& data,int linesize)
{
    std::copy(data.begin(),data.end(),LineWriter(std::cout,linesize));
}

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