Re: Delete chars in a file stream

"Bernie" <indico(at)gmx-topmail.de> wrote in message
news:4852328d$1_7@news.bluewin.ch...


[Not thoroughly tested; error checking omitted for brevity]:

#include <cstdio>
#include <fstream>
#include <ios>
#include <iostream>
#include <iterator>
#include <string>

void remove_last_n(const std::string& filename,
                   std::streamsize n)
{
    std::string temp(std::tmpnam(0));
    std::ifstream in(filename.c_str());
    std::ofstream out(temp.c_str());
    std::istream_iterator<char> itstart(in);
    std::istream_iterator<char> itend;

    std::iterator_traits<std::istream_iterator<char> >
        ::distance_type size(std::distance(itstart, itend));

    if(size > n)
    {
        std::streamsize new_size(size - n);
        in.clear();
        in.seekg(0);

        for(std::streamsize i = 0; i < new_size; ++i)
            out.put(in.get());

        in.clear();
        in.close();
        out.close();
        std::remove(filename.c_str());
        std::rename(temp.c_str(), filename.c_str());
    }
}

int main()
{
    remove_last_n("test.txt", 5);
    return 0;
}

-Mike