Read binary file into vector

Question

I found several answers on how to do it but my question is why I get a difference from using C FILE functions or using the stream read function.

If I do the following:

auto  fp = fopen( read_file.c_str(), "rb" );
fseek( fp, 0, SEEK_END );
auto  file_sz = ftell( fp );

std::vector< unsigned char > data( file_sz, 0 );

fseek( fp, 0, SEEK_SET );
fread( &data.at( 0 ), 1, file_sz, fp );
fclose( fp );

then data has 10384 values which matches file_sz.

If I do:

std::ifstream  orig_file( read_file, std::ios_base::binary );

if( orig_file.fail() )
    {
    std::cout << "Error Opening Input File [" << read_file << "]. " << strerror( errno ) << "\n";
    return;
    }

orig_file.seekg( 0, std::ios::end );
auto len = orig_file.tellg();
orig_file.seekg( 0, std::ios::beg );

std::vector< unsigned char >
                        data( len );
orig_file.read( ( char * )&data[ 0 ], len );

then data has the same 10384 bytes, but if I do the following:

std::istream_iterator< unsigned char >
                            it_begin( orig_file );
std::istream_iterator< unsigned char >
                            it_end;
std::vector< unsigned char >
                            data( it_begin, it_end );

or

data.assign( it_begin, std::istream_iterator< unsigned char >() );

data only has 10374 bytes. Thanks.

I don't understand how 9 bytes are lost when being inserted into the vector. Can you help explain that to me?

My guess is you have something that is being treated as white space at the end of the file. What happens if you try [this](http://stackoverflow.com/questions/17022096/input-iterator-skipping-whitespace-any-way-to-prevent-this-skipping) — NathanOliver, Aug 25 '16 at 14:34
check out this http://en.cppreference.com/w/cpp/iterator/istream_iterator It skips whitespaces by default, to disable http://en.cppreference.com/w/cpp/io/manip/skipws — Denis Zaikin, Aug 25 '16 at 14:36

Read binary file into vector

0 Answers0