fixed and improved single buffer version, added seeking as well

fdiobuf.cpp

@@ -37,6 +37,8 @@ std::streambuf::int_type sc::io::fdiobuf::overflow(std::streambuf::int_type c) {
 			std::cerr << "write result = " << res << ", errno = " << errno << '\n';
 		}
 	}
+	_ch = c;
+	setp(&_ch, &_ch + 1);
 	return c;
 }
 
@@ -48,3 +50,28 @@ std::streamsize sc::io::fdiobuf::xsputn(const char* s, std::streamsize num) {
 	}
 	return res;
 }
+
+std::streambuf::pos_type sc::io::fdiobuf::seekoff(std::streambuf::off_type off,
+												  std::ios_base::seekdir dir,
+												  std::ios_base::openmode /*which*/) {
+	int whence;
+	switch (dir) {
+		case std::ios_base::beg: whence = SEEK_SET; break;
+		case std::ios_base::end: whence = SEEK_END; break;
+		case std::ios_base::cur: whence = SEEK_CUR; break;
+		default: throw std::runtime_error("invalid seekdir");
+	}
+	return ::lseek(_fd, off, whence);
+}
+
+std::streambuf::pos_type sc::io::fdiobuf::seekpos(std::streambuf::pos_type pos,
+												  std::ios_base::openmode /*which*/) {
+	return ::lseek(_fd, pos, SEEK_SET);
+}
+
+std::streambuf::int_type sc::io::fdiobuf::pbackfail(std::streambuf::int_type /*c*/) {
+	if (::lseek(_fd, -1, SEEK_CUR) == -1) {
+		return EOF;
+	}
+	return 0;
+}

libscio.hpp

@@ -40,6 +40,15 @@ namespace sc {
 				// output
 				int_type overflow(int_type c) override;
 				std::streamsize xsputn(const char* s, std::streamsize num) override;
+
+				// stream offset positioning
+				pos_type seekoff(off_type off,
+								 std::ios_base::seekdir dir,
+								 std::ios_base::openmode which
+								 = std::ios_base::in | std::ios_base::out) override;
+				pos_type seekpos(pos_type pos, std::ios_base::openmode which
+								 = std::ios_base::in | std::ios_base::out) override;
+				int_type pbackfail(int_type c = EOF) override;
 		};
 
 		class fdostream : public std::ostream {