Add operator<<(ostream, exception)

1 files changed, 68 insertions, 0 deletions

diff --git a/butl/utility.cxx b/butl/utility.cxx
index d684553..d971a3f 100644
--- a/butl/utility.cxx
+++ b/butl/utility.cxx
@@ -2,6 +2,8 @@
 // copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
 // license   : MIT; see accompanying LICENSE file
 
+#include <ostream>
+
 #include <butl/utility>
 
 namespace butl
@@ -22,3 +24,69 @@ namespace butl
 
 #endif
 }
+
+namespace std
+{
+  using namespace butl;
+
+  ostream&
+  operator<< (ostream& o, const exception& e)
+  {
+    const char* d (e.what ());
+    const char* s (d);
+
+    // Strip the leading junk (colons and spaces).
+    //
+    // Note that error descriptions for ios_base::failure exceptions thrown by
+    // fdstream can have the ': ' prefix for libstdc++ (read more in comment
+    // for throw_ios_failure()).
+    //
+    for (; *s == ' ' || *s == ':'; ++s) ;
+
+    // Strip the trailing junk (periods, spaces, newlines).
+    //
+    // Note that msvcrt adds some junk like this:
+    //
+    // Invalid data.\r\n
+    //
+    size_t n (string::traits_type::length (s));
+    for (; n > 0; --n)
+    {
+      switch (s[n-1])
+      {
+      case '\r':
+      case '\n':
+      case '.':
+      case ' ': continue;
+      }
+
+      break;
+    }
+
+    // Lower-case the first letter if the beginning looks like a word (the
+    // second character is the lower-case letter or space).
+    //
+    char c;
+    bool lc (n > 0 && alpha (c = s[0]) && c == ucase (c) &&
+             (n == 1 || (alpha (c = s[1]) && c == lcase (c)) || c == ' '));
+
+    // Print the description as is if no adjustment is required.
+    //
+    if (!lc && s == d && s[n] == '\0')
+      o << d;
+    else
+    {
+      // We need to produce the resulting description and then write it
+      // with a single formatted output operation.
+      //
+      string r (s, n);
+
+      if (lc)
+        r[0] = lcase (r[0]);
+
+      o << r;
+    }
+
+    return o;
+  }
+}