Splitting files in C++ - c++

Question

I need to split a file into multiple files without compression. I found this on cpp reference
#include <fstream>
using namespace std;
int main () {
char * buffer;
long size;
ifstream infile ("test.txt",ifstream::binary);
ofstream outfile ("new.txt",ofstream::binary);
// get size of file
infile.seekg(0,ifstream::end);
size=infile.tellg();
infile.seekg(0);
// allocate memory for file content
buffer = new char [size];
// read content of infile
infile.read (buffer,size);
// write to outfile
outfile.write (buffer,size);
// release dynamically-allocated memory
delete[] buffer;
outfile.close();
infile.close();
return 0;
}
and I thought to do it like this. But the problem is ..I can create only the 1st file because I can read data only from the beginning of the file. Can it be done like this and if no..what is the best way to split these files.

Answer 1

The example code doesn't split a file into multiple files; it just
copies the file. To split a file into multiple files, just don't close
the input. In pseudo-code:
open input
decide size of each block
read first block
while block is not empty (read succeeded):
open new output file
write block
close output file
read another block
The important part is not closing the input file, so that each read
picks up exactly where the preceding read ended.

Answer 2

You can seek the stream to the desired position and then read stream. Check this piece of code.
// get size of file
infile.seekg(0,ifstream::end);
size=infile.tellg();
infile.seekg(0);
All you need to do is to remember the position where you stopped reading infile, close outfile, open new outfile, reallocate buffers and read infile to buffer and write to second outfile.

Answer 3

You can read data from anywhere in the file - you already moved to the end and back to the start successfully.
You don't need to though: just write a loop to sequentially read each outputSize and write it to a new file, for some outputSize < size.

Answer 4

Why reinvent the wheel - Try split
Even has the source code for you to get ideas if you want to implement it in C++

Answer 5

I think I have got a solution to your problem...
You read all the first file in a char array.
Then you write the first half of your array in a file, and then second half of you array in other file...
For example :
#include <fstream>
using namespace std;
int main () {
char * buffer;
long size;
ifstream infile ("test.txt",ifstream::binary);
ofstream outfile ("new.txt",ofstream::binary);
ofstream outfile2 ("new2.txt",ofstream::binary);
// get size of file
infile.seekg(0,ifstream::end);
size=infile.tellg();
infile.seekg(0);
// allocate memory for file content
buffer = new char [size];
// read content of infile
infile.read (buffer,size);
// write to outfile
outfile.write (buffer,size/2);
outfile2.write (buffer+size/2,size);
// release dynamically-allocated memory
delete[] buffer;
outfile.close();
infile.close();
outfile2.close();
return 0;
}
You can also read the first half, write it, then read the second half and write it... Just have a look to that :
int main () {
char * buffer;
long size;
long halfSize;
ifstream infile ("test.txt",ifstream::binary);
ofstream outfile ("new.txt",ofstream::binary);
ofstream outfile2 ("new2.txt",ofstream::binary);
// get size of file
infile.seekg(0,ifstream::end);
size=infile.tellg();
infile.seekg(0);
halfSize = static_cast<int>(floor(size/2));
// allocate memory for file content
buffer1 = new char[halfSize];
buffer2 = new char[size-halfSize];
// read content of infile
infile.read (buffer1,halfSize);
infile.read (buffer2,size-halfSize);
// write to outfile
outfile.write (buffer1,halfSize);
outfile2.write (buffer2,size-halfSize);
// release dynamically-allocated memory
delete[] buffer;
delete[] buffer2;
outfile.close();
infile.close();
outfile2.close();
return 0;
}