Explicit error for comments, with README link

README.rst

@@ -110,7 +110,7 @@ Interaction with the C preprocessor
 -----------------------------------
 
 In order to be compilable, C code must be preprocessed by the C preprocessor -
-``cpp``. ``cpp`` handles preprocessing directives like ``#include`` and
+``cpp``. A compatible ``cpp`` handles preprocessing directives like ``#include`` and
 ``#define``, removes comments, and performs other minor tasks that prepare the C
 code for compilation.
 

pycparser/c_lexer.py

@@ -209,6 +209,10 @@ def _make_tok_location(self, token):
 
     bad_octal_constant = '0[0-7]*[89]'
 
+    # comments are not supported
+    unsupported_c_style_comment = r'\/\*'
+    unsupported_cxx_style_comment = r'\/\/'
+
     # character constants (K&R2: A.2.5.2)
     # Note: a-zA-Z and '.-~^_!=&;,' are allowed as escape chars to support #line
     # directives with Windows paths as filenames (..\..\dir\file)
@@ -475,6 +479,16 @@ def t_BAD_CONST_OCT(self, t):
         msg = "Invalid octal constant"
         self._error(msg, t)
 
+    @TOKEN(unsupported_c_style_comment)
+    def t_UNSUPPORTED_C_STYLE_COMMENT(self, t):
+        msg = "Comments are not supported, see https://github.com/eliben/pycparser#3using."
+        self._error(msg, t)
+
+    @TOKEN(unsupported_cxx_style_comment)
+    def t_UNSUPPORTED_CXX_STYLE_COMMENT(self, t):
+        msg = "Comments are not supported, see https://github.com/eliben/pycparser#3using."
+        self._error(msg, t)
+
     @TOKEN(octal_constant)
     def t_INT_CONST_OCT(self, t):
         return t

tests/README.txt

@@ -1 +1 @@
-Run 'python -m unittest discover' from the root pycparser directory
+Run 'python3 -m unittest discover' from the root repository directory.

tests/test_c_lexer.py

@@ -418,11 +418,12 @@ def test_preprocessor_pragma(self):
 ERR_FILENAME_BEFORE_LINE    = 'filename before line'
 ERR_LINENUM_MISSING         = 'line number missing'
 ERR_INVALID_LINE_DIRECTIVE  = 'invalid #line directive'
+ERR_COMMENT                 = 'Comments are not supported'
 
 
 class TestCLexerErrors(unittest.TestCase):
     """ Test lexing of erroneous strings.
-        Works by passing an error functions that saves the error
+        Works by passing an error function that saves the error
         in an attribute for later perusal.
     """
     def error_func(self, msg, line, column):
@@ -496,6 +497,9 @@ def test_preprocessor(self):
         self.assertLexerError('#line "ka"', ERR_FILENAME_BEFORE_LINE)
         self.assertLexerError('#line df', ERR_INVALID_LINE_DIRECTIVE)
         self.assertLexerError('#line \n', ERR_LINENUM_MISSING)
+        # a compatible preprocessor must remove comments.
+        self.assertLexerError('//', ERR_COMMENT)
+        self.assertLexerError('/*', ERR_COMMENT)
 
 
 if __name__ == '__main__':