C ++将ifstream管道化为stringstream

Question

I am overloading my istream operator, so I can replace std::cin with my object. I know I will have to feed it an empty stringstream for the final output to work.

I would like to feed an std::ifstream into a std::stringstream as so:

while(ifs >> ss) {}

Is this possible? Here is an example prototype code:

friend istream & operator >> (istream & is, Database & db)
{
    ifstream ifs;
    ifs.open(db.inputFilename_, ios::in | ios::binary);
    if (!ifs.is_open())
    {
        cout << "Couldn't read " << db.inputFilename_ << endl;
        return is;
    }
    while (ifs >> db.iss)
    {}
    ifs.close()
    return db.iss;
}

I am not interested in any answers that start with "use Boost" :) This is a purely standard C++ project. Thank you for any help or pointers.

Right now I am getting:

error: invalid operands to binary expression ('ifstream' (aka 'basic_ifstream<char>') and 'istringstream' (aka 'basic_istringstream<char>'))

Answer 1

Simply do this:

 if(ifs){
     db.iss << ifs.rdbuf();    
     ifs.close();
 }

Answer 2

You can use std::copy with an std::istream_iterator for std::cin and std::ostream_iterator for the std::stringstream .

#include <algorithm>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <sstream>

void redirect(std::ifstream &is, std::stringstream &os) {
    is >> std::noskipws;
    std::istream_iterator<char> begin(is);
    std::istream_iterator<char> end;
    std::ostream_iterator<char> out(os);
    std::copy(begin, end, out);
}

Note that this copies the entire file into the std::stringstream , and thus for really large files that can't fit in memory, this will fail. The rdbuf solution that NaCl gave will similarly have an issue with very large files.

You can solve the large file problem by not reading all of the input at once. However, this will most likely require you to restructure your code inside your parsers. Without more detail on their implementations, I can't point you in the right direction.