changed fdstream documentation, added FAIL_FD constant, fallback file descriptor is now optional

alib2std/src/extensions/fdstream.cpp

@@ -6,6 +6,8 @@
 namespace std {
+const int FAIL_FD = -1;
+
 fdstreambuf::fdstreambuf ( int fd ) : fd ( fd ) {
 	setp ( buff.begin ( ), buff.end ( ) - 1 );
 }
@@ -61,7 +63,7 @@ bool fdaccessor::is_redirected ( ) const {
 	return redirected;
 }
-ofdstream::ofdstream ( int fd, int fallback_fd ) : fda ( fd, fallback_fd ), fdbuf ( fda.get_fd ( ) ) {
+ofdstream::ofdstream ( int fd, int fallback_fd = FAIL_FD) : fda ( fd, fallback_fd ), fdbuf ( fda.get_fd ( ) ) {
 	this->init ( & fdbuf );
 	if ( fda.get_fd ( ) == -1 )

alib2std/src/extensions/fdstream.hpp

@@ -4,12 +4,14 @@
 /*
  * ofdstream
- * ofdstream takes a file descriptor (fd) by constructor to use for output
- * if the file descriptor is not valid for any reason during construction of the ofdstream, ofdstream will set its state to ios::fail
- * if the file descriptor is valid, it is used for successive buffered output
+ * ofdstream takes a primary file descriptor (fd) and fallback file descriptor by constructor to use for output
+ * if the primary fd is not valid for any reason, ofdstream will try to use fallback fd, if even fallback fd is not valid, ofdstream sets its state to ios::fail
+ * if the primary fd (or fallback fd) is valid , it is used for successive buffered output
  *
  * supplied file descriptor has to be already open in order for ofdstream to work
  * ofdstream does not close the file descriptor and does not change internal flags of the file descriptor during the lifetime of ofdstream and during destruction of ofdstream
+ *
+ * typical use is to use as primary fd some arbitrary fd (5) and for fallback fd some standard fd (2) if we wish to see the output
  */
 #ifndef FDSTREAM_HPP_
@@ -22,6 +24,8 @@
 namespace std {
+extern const int FAIL_FD;
+
 class fdstreambuf : public streambuf {
 	static const size_t buff_sz = 512;