Add char-scanner to libbutl, use in libbpkg and build2

1 files changed, 78 insertions, 0 deletions

diff --git a/butl/char-scanner.cxx b/butl/char-scanner.cxx
new file mode 100644
index 0000000..1561ad1
--- /dev/null
+++ b/butl/char-scanner.cxx
@@ -0,0 +1,78 @@
+// file      : butl/char-scanner.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2015 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#include <butl/char-scanner>
+
+#include <istream>
+
+using namespace std;
+
+namespace butl
+{
+  auto char_scanner::
+  peek () -> xchar
+  {
+    if (unget_)
+      return buf_;
+    else
+    {
+      if (eos_)
+        return xchar (xchar::traits_type::eof (), line, column);
+      else
+      {
+        xchar::int_type v (is_.peek ());
+
+        if (v == xchar::traits_type::eof ())
+          eos_ = true;
+
+        return xchar (v, line, column);
+      }
+    }
+  }
+
+  auto char_scanner::
+  get () -> xchar
+  {
+    if (unget_)
+    {
+      unget_ = false;
+      return buf_;
+    }
+    else
+    {
+      // When is_.get () returns eof, the failbit is also set (stupid,
+      // isn't?) which may trigger an exception. To work around this
+      // we will call peek() first and only call get() if it is not
+      // eof. But we can only call peek() on eof once; any subsequent
+      // calls will spoil the failbit (even more stupid).
+      //
+      xchar c (peek ());
+
+      if (!eos (c))
+      {
+        is_.get ();
+
+        if (c == '\n')
+        {
+          line++;
+          column = 1;
+        }
+        else
+          column++;
+      }
+
+      return c;
+    }
+  }
+
+  void char_scanner::
+  unget (const xchar& c)
+  {
+    // Because iostream::unget cannot work once eos is reached,
+    // we have to provide our own implementation.
+    //
+    buf_ = c;
+    unget_ = true;
+  }
+}