[cfe-dev] Premature EOF when reading binary file

[Simon Peter]

Hi,

I'm using libc++ inside the Barrelfish[1] operating system, compiled 
using g++ 4.4.5.

When reading a binary file using the read() method on a regular fstream 
object, I sometimes get an EOF prematurely, e.g.:

     uint64_t actual_size = 1234;
     char *data = (char*) malloc(actual_size);

     fstream binary_file(file_path, ios::in|ios::binary);
     binary_file.read(data, actual_size);

This won't read the complete file into the buffer and sets the EOF bit 
on the stream. The file is longer than 1234 bytes.

I tracked the problem down to the implicit cast in fstream, line 582:

     __c = *this->gptr();

In this case, this->gptr() returns a 'char *' to the next available 
character in the input stream, while __c is an 'int'. The implicit cast 
ends up converting the input character to -1 (a valid character in the 
input stream), which coincides with traits_type::eof() and is thus 
treated as an end-of-file indication.

I am unsure how to fix this and would be grateful for suggestions.

Thanks!
Simon

[1] http://www.barrelfish.org/