Thread: How to read a file stream entirely into a vector?

I've got a file to read, well, read to a vector<short> m_vVoice;

we all know that

1 ) ios_base->ios->istream->ifstream

2 ) istream& read ( char* s, streamsize n );


So, I tried the following code

Code:

ifstream ifs (fn.c_str (), ios::binary);


// 1) -- fail
// copy(istream_iterator<short>(ifs),istream_iterator<short>(),back_inserter(this->m_vVoice));

// 2) -- fail
// vector<short>::iterator currentPos = this->m_vVoice.begin();
// ifs.read (reinterpret_cast <char *>(&currentPos), this->m_iVoiceLength * sizeof(short));

// 3) -- works, but too slow
// http://www.thescripts.com/forum/thread133371.html, clumsy way
for(int i = 0; i < this->m_iVoiceLength; i++)
{
ifs.read( reinterpret_cast <char *> (&this->m_vVoice), sizeof (short) );
}

The first two methods are trying to read a whole/entire block of memory directly into vector<short> m_vVoice, but failed; the 3rd method is running, but it actually read data one by one. It's pretty slow, which is not what I expected.

Can anybody help??

Best Regards
JIA Pei

Originally Posted by jiapei100

The first two methods are trying to read a whole/entire block of memory directly into vector<short> m_vVoice, but failed; the 3rd method is running, but it actually read data one by one. It's pretty slow, which is not what I expected.

Why not just read all the data in that third example, instead of a single short?

Code:

#include <fstream>
#include <vector>
#include <string>
#include <algorithm>

int main( void ) {
  std::ifstream in( "shorts.txt", std::ios::binary );

  if ( in ) {
    std::vector<short> vs;
    vs.insert( vs.begin(), std::istream_iterator<short>(in), std::istream_iterator<short>() );
    std::copy( vs.begin(), vs.end(), std::ostream_iterator<int>(std::cout, "\n"));
  }

  return 0;
}

The trick is to use insert.

Assuming your file actually contains shorts rather than text, try something like this:

Code:

ifstream inputFile( "shorts.txt", std::ios::binary );
vector<short> shorts( (istreambuf_iterator<short>( inputFile )), istreambuf_iterator<short>() );