[lmi-commits] [lmi] master a102012 6/6: Generally avoid using null_stream()

[Greg Chicares]

branch: master
commit a10201200bcabb409be97e0ef6265c5d9850b2b9
Author: Gregory W. Chicares <gchicares@sbcglobal.net>
Commit: Gregory W. Chicares <gchicares@sbcglobal.net>

    Generally avoid using null_stream()
---
 null_stream.cpp       | 15 +++++++++++++++
 system_command_wx.cpp |  4 ++--
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/null_stream.cpp b/null_stream.cpp
index 70eeca3..4df8a92 100644
--- a/null_stream.cpp
+++ b/null_stream.cpp
@@ -69,6 +69,21 @@ std::streambuf& null_streambuf()
     return z;
 }
 
+/// Reference to a static null stream--see caveat.
+///
+/// Caveat: The static object is in effect a global variable.
+/// Replacing its streambuf by calling rdbuf(another_streambuf)
+/// therefore has a global effect that is probably unwanted.
+/// Therefore, prefer to create a local object instead, e.g.:
+///   std::ostream local_os(&null_streambuf());
+///   local_os << "written to oblivion";
+///   local_os.rdbuf(std::cout.rdbuf); // effect is only local
+///   local_os << "written to stdout";
+///
+/// This is only intended to be used as a default ostream& argument:
+///   foo(std::ostream& os = null_stream());
+/// for functions that never change the streambuf.
+
 std::ostream& null_stream()
 {
     static std::ostream z(&null_streambuf());
diff --git a/system_command_wx.cpp b/system_command_wx.cpp
index d401c9d..d9c550e 100644
--- a/system_command_wx.cpp
+++ b/system_command_wx.cpp
@@ -25,7 +25,6 @@
 
 #include "alert.hpp"
 #include "force_linking.hpp"
-#include "null_stream.hpp"
 #include "timer.hpp"
 
 #include <wx/app.h>                     // wxTheApp
@@ -88,7 +87,8 @@ void concrete_system_command(std::string const& cmd_line)
         : nullptr;
         ;
     bool const b = f && f->GetStatusBar();
-    std::ostream& statusbar_if_available = b ? status() : null_stream();
+    std::ostream null_output(0);
+    std::ostream& statusbar_if_available = b ? status() : null_output;
 
     statusbar_if_available << "Running..." << std::flush;
     wxArrayString output;