Concatenate two huge files in C++

Question

I have two std::ofstream text files of a hundred plus megs each and I want to concatenate them. Using fstreams to store the data to create a single file usually ends up with an

Answer 1

It really depends whether you wish to use "pure" C++ for this, personally at the cost of portability I would be tempted to write:

#include 
#include 

int main(int argc, char* argv[]) {
    std::ostringstream command;

    command << "cat "; // Linux Only, command for Windows is slightly different

    for (int i = 2; i < argc; ++i) { command << argv[i] << " "; }

    command << "> ";

    command << argv[1];

    return system(command.str().c_str());
}

Is it good C++ code ? No, not really (non-portable and does not escape command arguments).

But it'll get you way ahead of where you are standing now.

As for a "real" C++ solution, with all the ugliness that streams could manage...

#include 
#include 

static size_t const BufferSize = 8192; // 8 KB

void appendFile(std::string const& outFile, std::string const& inFile) {
    std::ofstream out(outFile, std::ios_base::app |
                               std::ios_base::binary |
                               std::ios_base::out);

    std::ifstream in(inFile, std::ios_base::binary |
                             std::ios_base::in);

    std::vector buffer(BufferSize);
    while (in.read(&buffer[0], buffer.size())) {
        out.write(&buffer[0], buffer.size());
    }

    // Fails when "read" encounters EOF,
    // but potentially still writes *some* bytes to buffer!
    out.write(&buffer[0], in.gcount());
}