Catch exceptions as const references (fixes #236)

This fix allows qpdf to compile/test cleanly with gcc 8.

examples/pdf-split-pages.cc

@@ -77,7 +77,7 @@ int main(int argc, char* argv[])
     {
         process(whoami, argv[1], argv[2]);
     }
-    catch (std::exception e)
+    catch (std::exception const& e)
     {
         std::cerr << whoami << ": exception: " << e.what() << std::endl;
         return 2;

libqpdf/MD5.cc

@@ -421,7 +421,7 @@ MD5::checkFileChecksum(char const* const checksum,
 	std::string actual_checksum = getFileChecksum(filename, up_to_size);
 	result = (checksum == actual_checksum);
     }
-    catch (std::runtime_error)
+    catch (std::runtime_error const&)
     {
 	// Ignore -- return false
     }

libtests/qutil.cc

@@ -26,7 +26,7 @@ void test_to_number(char const* str, int_T wanted, bool error,
         result = fn(str);
         worked = (wanted == result);
     }
-    catch (std::runtime_error)
+    catch (std::runtime_error const&)
     {
         threw = true;
     }
@@ -247,7 +247,7 @@ void same_file_test()
         fclose(QUtil::safe_fopen("qutil.out", "r"));
         fclose(QUtil::safe_fopen("other-file", "r"));
     }
-    catch (std::exception)
+    catch (std::exception const&)
     {
         std::cout << "same_file_test expects to have qutil.out and other-file"
             " exist in the current directory\n";

qpdf/qpdf.cc

@@ -773,7 +773,7 @@ static std::vector<int> parse_numrange(char const* range, int max,
             }
         }
     }
-    catch (std::runtime_error e)
+    catch (std::runtime_error const& e)
     {
         if (throw_error)
         {
@@ -1372,7 +1372,7 @@ static void parse_rotation_parameter(Options& o, std::string const& parameter)
         parse_numrange(range.c_str(), 0, true);
         range_valid = true;
     }
-    catch (std::runtime_error)
+    catch (std::runtime_error const&)
     {
         // ignore
     }

qpdf/test_driver.cc

@@ -717,7 +717,7 @@ void runtest(int n, char const* filename1, char const* arg2)
 	    // Do it wrong first...
 	    pdf.replaceObject(qdict.getObjGen(), qdict);
 	}
-	catch (std::logic_error)
+	catch (std::logic_error const&)
 	{
 	    std::cout << "caught logic error as expected" << std::endl;
 	}
@@ -1003,7 +1003,7 @@ void runtest(int n, char const* filename1, char const* arg2)
             res2.unparseResolved();
             std::cout << "oops -- didn't throw" << std::endl;
         }
-        catch (std::logic_error e)
+        catch (std::logic_error const& e)
         {
             std::cout << "logic error: " << e.what() << std::endl;
         }
@@ -1012,7 +1012,7 @@ void runtest(int n, char const* filename1, char const* arg2)
             res2.makeDirect();
             std::cout << "oops -- didn't throw" << std::endl;
         }
-        catch (std::logic_error e)
+        catch (std::logic_error const& e)
         {
             std::cout << "logic error: " << e.what() << std::endl;
         }
@@ -1109,7 +1109,7 @@ void runtest(int n, char const* filename1, char const* arg2)
             pdf.copyForeignObject(pdf.getTrailer().getKey("/QTest"));
             std::cout << "oops -- didn't throw" << std::endl;
         }
-        catch (std::logic_error e)
+        catch (std::logic_error const& e)
         {
             std::cout << "logic error: " << e.what() << std::endl;
         }
@@ -1118,7 +1118,7 @@ void runtest(int n, char const* filename1, char const* arg2)
             pdf.copyForeignObject(QPDFObjectHandle::newInteger(1));
             std::cout << "oops -- didn't throw" << std::endl;
         }
-        catch (std::logic_error e)
+        catch (std::logic_error const& e)
         {
             std::cout << "logic error: " << e.what() << std::endl;
         }
@@ -1139,7 +1139,7 @@ void runtest(int n, char const* filename1, char const* arg2)
             w.write();
             std::cout << "oops -- didn't throw" << std::endl;
         }
-        catch (std::logic_error e)
+        catch (std::logic_error const& e)
         {
             std::cout << "logic error: " << e.what() << std::endl;
         }
@@ -1185,7 +1185,7 @@ void runtest(int n, char const* filename1, char const* arg2)
             QPDFObjectHandle::parse("[1 0 R]", "indirect test");
             std::cout << "oops -- didn't throw" << std::endl;
         }
-        catch (std::logic_error e)
+        catch (std::logic_error const& e)
         {
             std::cout << "logic error parsing indirect: " << e.what()
                       << std::endl;
@@ -1195,7 +1195,7 @@ void runtest(int n, char const* filename1, char const* arg2)
             QPDFObjectHandle::parse("0 trailing", "trailing test");
             std::cout << "oops -- didn't throw" << std::endl;
         }
-        catch (std::runtime_error e)
+        catch (std::runtime_error const& e)
         {
             std::cout << "trailing data: " << e.what()
                       << std::endl;