c++ - file stream tellg/tellp and gcc-4.6 is this a bug? -

this code:

#include <iostream> #include <cstdio> #include <fstream> #include <string>  int main() {        std::remove("test.txt");     std::fstream f("test.txt",std::ios::in | std::ios::out | std::ios::binary | std::ios::trunc);     std::cout << f.good() << std::endl;     f<<"test"<< std::flush;     std::cout << f.tellg() << " " << f.tellp() << std::endl;     f.seekg(0);     std::string s;     f>>s;     std::cout << f.tellg() << " " << f.tellp() << std::endl; }    

gives following output in gcc-4.4.5

1 4 4 4 4 

i.e. both tellg , tellp returned expected stream position 4.

while gcc-4.6.0

gives:

1 4 4 -1 4 

where can find reference tell:

1. 1st case correct (bug in gcc-4.6)
2. 2nd case correct (bug in gcc < gcc-4.6)
3. both case correct behavior undefined

ok, not bug, seems required behavior:

according c++ 2003 standard:

• tellg(): (27.6.1.3)

  after constructing sentry object, if fail() != false, returns pos_type(-1) indicate failure. otherwise, returns rdbuf()->pubseekoff(0, cur, in).

• sentry (27.6.1.1.2):

  if noskipws 0 , is.flags() & ios_base::skipws nonzero, func- tion extracts , discards each character long next available input character c whitespace character. if is.rdbuf()->sbumpc() or is.rdbuf()->sgetc() returns traits::eof(), function calls setstate(failbit | eofbit) (which may throw ios_base::failure).

so

• tellg() creates sentry object:
• sentry extracts white space characters , should set failbit after getting eof.
• tellg() sees failbit should return eof() (-1)

so gcc-4.6 seems behave correctly...