Catch exception objects by const reference

A version of SqliteModernCpp#160 on the `dev` branch.

Author: zauguin

README.md

@@ -83,7 +83,7 @@ int main() {
       db << "select count(*) from user" >> str_count;
       cout << "scount : " << str_count << endl;
    }
-   catch (exception& e) {
+   catch (const exception& e) {
       cout << e.what() << endl;
    }
 }
@@ -286,7 +286,7 @@ int main() {
 
       // Even more queries ..
    }
-   catch (exception& e) { cout << e.what() << endl; }
+   catch (const exception& e) { cout << e.what() << endl; }
 }
 ```
 
@@ -388,14 +388,14 @@ try {
 }
 /* if you are trying to catch all sqlite related exceptions
  * make sure to catch them by reference */
-catch (sqlite_exception& e) {
+catch (const sqlite_exception& e) {
    cerr  << e.get_code() << ": " << e.what() << " during "
          << e.get_sql() << endl;
 }
 /* you can catch specific exceptions as well,
-   catch(sqlite::errors::constraint e) {  } */
+   catch(const sqlite::errors::constraint &e) {  } */
 /* and even more specific exceptions
-   catch(sqlite::errors::constraint_primarykey e) {  } */
+   catch(const sqlite::errors::constraint_primarykey &e) {  } */
 ```
 
 You can also register a error logging function with `sqlite::error_log`.
@@ -419,7 +419,7 @@ try {
    // inserting again to produce error
    db << "insert into person (id, name) values (?,?)" << 1 << "jack";
 }
-catch (sqlite_exception& e) {}
+catch (const sqlite_exception& e) {}
 ```
 
 Custom SQL functions

hdr/sqlite_modern_cpp.h

@@ -526,10 +526,10 @@ namespace sqlite {
 				if(!ctxt->constructed) new(ctxt) AggregateCtxt<ContextType>();
 				step<Count, Functions>(db, count, vals, ctxt->obj);
 				return;
-			} catch(sqlite_exception &e) {
+			} catch(const sqlite_exception &e) {
 				sqlite3_result_error_code(db, e.get_code());
 				sqlite3_result_error(db, e.what(), -1);
-			} catch(std::exception &e) {
+			} catch(const std::exception &e) {
 				sqlite3_result_error(db, e.what(), -1);
 			} catch(...) {
 				sqlite3_result_error(db, "Unknown error", -1);
@@ -590,10 +590,10 @@ namespace sqlite {
 				if(!ctxt->constructed) new(ctxt) AggregateCtxt<ContextType>();
 				store_result_in_db(db,
 						static_cast<Functions*>(sqlite3_user_data(db))->second(ctxt->obj));
-			} catch(sqlite_exception &e) {
+			} catch(const sqlite_exception &e) {
 				sqlite3_result_error_code(db, e.get_code());
 				sqlite3_result_error(db, e.what(), -1);
-			} catch(std::exception &e) {
+			} catch(const std::exception &e) {
 				sqlite3_result_error(db, e.what(), -1);
 			} catch(...) {
 				sqlite3_result_error(db, "Unknown error", -1);
@@ -641,10 +641,10 @@ namespace sqlite {
 			try {
 				store_result_in_db(db,
 						(*static_cast<Function*>(sqlite3_user_data(db)))(std::forward<Values>(values)...));
-			} catch(sqlite_exception &e) {
+			} catch(const sqlite_exception &e) {
 				sqlite3_result_error_code(db, e.get_code());
 				sqlite3_result_error(db, e.what(), -1);
-			} catch(std::exception &e) {
+			} catch(const std::exception &e) {
 				sqlite3_result_error(db, e.what(), -1);
 			} catch(...) {
 				sqlite3_result_error(db, "Unknown error", -1);

tests/error_log.cc

@@ -43,7 +43,7 @@ TEST_CASE("error_log works", "[log]") {
         db << "INSERT INTO person (id,name) VALUES (?,?)" << 1 << "jack";
         // triger primarykey constraint of 'id'
         db << "INSERT INTO person (id,name) VALUES (?,?)" << 1 << "bob";
-      } catch (errors::constraint& e) { }
+      } catch (const errors::constraint& e) { }
       REQUIRE(track.primarykey_called == true);
       REQUIRE(track.constraint_called == false);
       track.primarykey_called = false;
@@ -54,7 +54,7 @@ TEST_CASE("error_log works", "[log]") {
         db << "INSERT INTO person (id,name) VALUES (?,?)" << 1 << "jack";
         // trigger unique constraint of 'name'
         db << "INSERT INTO person (id,name) VALUES (?,?)" << 2 << "jack";
-      } catch (errors::constraint& e) { }
+      } catch (const errors::constraint& e) { }
 
       REQUIRE(track.primarykey_called == false);
       REQUIRE(track.constraint_called == true);

tests/mov_ctor.cc

@@ -24,7 +24,7 @@ TEST_CASE("database lifecycle", "move_ctor") {
 
   bool failed = false;
   try { dbFront dbf; }
-  catch(sqlite_exception& e) { failed = true; }
+  catch(const sqlite_exception& e) { failed = true; }
   catch(...) { failed = true; }
 
   REQUIRE(failed == false);

tests/sqlcipher.cc

@@ -37,7 +37,7 @@ TEST_CASE("sqlcipher works", "[sqlcipher]") {
         config.key = "DebugKey2";
         sqlcipher_database db(file.fname, config);
         db << "INSERT INTO foo VALUES (?, ?)" << 3 << "fail";
-    } catch(errors::notadb) {
+    } catch(const errors::notadb&) {
         failed = true;
         // Expected, wrong key
     }