Can't write the last part of a txt file to cout using ifstream

问题

The code below will print all of the text from the sample text file I'm using except for the last little snippet of it. I think this has something to do with the eof or the byte size I'm using not working as I expect.

#include <iostream>
#include <fstream>

using namespace std;

int main(int argc, char* argv[]){
int length;
char* buffer;

//get file stream and open local file.
ifstream stream;
stream.open("SampleFile.txt", ios::binary);
stream.seekg(0, ios::end);
length = stream.tellg();
stream.seekg(0, ios::beg);

//read stream 1024 bytes at a time until all bytes of file are used
buffer = new char[1024];
bool eof = false;
while(!eof)
{
    stream.read(buffer, 1024);
    cout.write(buffer, 1024);
    if(stream.eof())
        eof = true;
    //cout << i << endl;
    //cout.write(buffer, 1024);
}

stream.close();
delete[] buffer;
return 0;
}

What am I missing?

回答1:

As you already know, you have a wrong size of buffer. The other thing is the read of less than 1024 characters (going to happen at the end if your file doesn't have exactly n*1024 bytes). Take the advantage of istream::gcount which gives you number of characters extracted by last read:

char buffer[1024];
while(stream)
{
    stream.read(buffer, 1024);
    cout.write(buffer, stream.gcount());
}

回答2:

1) You are not correctly calcuulating the size of the final buffer.

2) You are not correctly recognizing all of the possible error conditions.

Try:

while(stream) {
    stream.read(buffer, 1024);
    cout.write(buffer, stream.gcount());
}

PS. If you are really trying to copy the named file to standard out, there is a much easier way:

ifstream stream("SampleFile.txt", ios::binary);
std::cout << stream.rdbuf();

回答3:

Looks like the problem is that your last read doesn't happen to be exactly the size of your buffer. You need to handle that as a special case. For details, see http://www.cplusplus.com/reference/iostream/istream/read/.

Oh, and it looks like your buffer is 8 bytes long but you read 1024 bytes. That's bad.

回答4:

Since you know the size of the file, why not read the entire file at once?

buffer = new char[length];

stream.read( buffer, length );
cout.write( buffer, length );

delete[] buffer;

来源：https://stackoverflow.com/questions/6740425/cant-write-the-last-part-of-a-txt-file-to-cout-using-ifstream

标签

c++

file-io

ifstream

cout

eof