[cfe-dev] Premature EOF when reading binary file

Howard Hinnant hhinnant at apple.com
Wed Feb 2 09:41:19 PST 2011

On Feb 2, 2011, at 10:47 AM, Simon Peter wrote:

> 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.  I've committed a fix to revision 124727.  Please let me know if that did not clear up the problem.


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