Release PGresult when an exception is thrown

Fix involves:
* Call PQclear in throw_postgresql_soci_error
* Change throw_postgresql_soci_error to take pointer by reference to
effectively reset result
* PostgreSQL tests pass
* Close #86
Rename res to result for consistency.

(std::unique_ptr would be bless for correct and simple RAII across SOCI)

src/backends/postgresql/error.cpp

@@ -28,11 +28,13 @@ std::string postgresql_soci_error::sqlstate() const
     return std::string(sqlstate_, 5);
 }
 
-void soci::details::postgresql::get_error_details(PGresult *res,
+void soci::details::postgresql::get_error_details(PGresult *result,
     std::string &msg, std::string &sqlstate)
 {
-    msg = PQresultErrorMessage(res);
-    const char *sqlst = PQresultErrorField(res, PG_DIAG_SQLSTATE);
+    assert(result);
+
+    msg = PQresultErrorMessage(result);
+    const char *sqlst = PQresultErrorField(result, PG_DIAG_SQLSTATE);
     const char* blank_sql_state = "     ";
     if (!sqlst)
     {
@@ -42,11 +44,13 @@ void soci::details::postgresql::get_error_details(PGresult *res,
     sqlstate.assign(sqlst, 5);
 }
 
-void soci::details::postgresql::throw_postgresql_soci_error(PGresult *res)
+void soci::details::postgresql::throw_postgresql_soci_error(PGresult*& result)
 {
     std::string msg;
     std::string sqlstate;
 
-    get_error_details(res, msg, sqlstate);
+    get_error_details(result, msg, sqlstate);
+    PQclear(result);
+    result = NULL;
     throw postgresql_soci_error(msg, sqlstate.c_str());
 }

src/backends/postgresql/error.h

@@ -19,9 +19,9 @@ namespace details
 namespace postgresql
 {
 
-void throw_postgresql_soci_error(PGresult *res);
+void throw_postgresql_soci_error(PGresult*& res);
 
-void get_error_details(PGresult *res, std::string &msg, std::string &sqlstate);
+void get_error_details(PGresult* res, std::string &msg, std::string &sqlstate);
 
 } // namespace postgresql
 

src/backends/postgresql/session.cpp

@@ -59,7 +59,6 @@ namespace // unnamed
 void hard_exec(PGconn * conn, char const * query, char const * errMsg)
 {
     PGresult* result = PQexec(conn, query);
-
     if (0 == result)
     {
         throw soci_error(errMsg);
@@ -68,6 +67,7 @@ void hard_exec(PGconn * conn, char const * query, char const * errMsg)
     ExecStatusType const status = PQresultStatus(result);
     if (PGRES_COMMAND_OK != status)
     {
+        // releases result with PQclear
         throw_postgresql_soci_error(result);
     }
 

src/backends/postgresql/statement.cpp

@@ -162,18 +162,19 @@ void postgresql_statement_backend::prepare(std::string const & query,
     {
         statementName_ = session_.get_next_statement_name();
 
-        PGresult * res = PQprepare(session_.conn_, statementName_.c_str(),
+        PGresult* result = PQprepare(session_.conn_, statementName_.c_str(),
             query_.c_str(), static_cast<int>(names_.size()), NULL);
-        if (res == NULL)
+        if (result == NULL)
         {
             throw soci_error("Cannot prepare statement.");
         }
-        ExecStatusType status = PQresultStatus(res);
+        ExecStatusType status = PQresultStatus(result);
         if (status != PGRES_COMMAND_OK)
         {
-            throw_postgresql_soci_error(res);
+            // releases result with PQclear
+            throw_postgresql_soci_error(result);
         }
-        PQclear(res);
+        PQclear(result);
     }
 
     stType_ = stType;
@@ -280,9 +281,7 @@ postgresql_statement_backend::execute(int number)
                 result_ = PQexecParams(session_.conn_, query_.c_str(),
                     static_cast<int>(paramValues.size()),
                     NULL, &paramValues[0], NULL, NULL, 0);
-
 #else
-
                 if (stType_ == st_repeatable_query)
                 {
                     // this query was separately prepared
@@ -318,6 +317,7 @@ postgresql_statement_backend::execute(int number)
                     ExecStatusType status = PQresultStatus(result_);
                     if (status != PGRES_COMMAND_OK)
                     {
+                        // releases result_ with PQclear
                         throw_postgresql_soci_error(result_);
                     }
                     PQclear(result_);
@@ -342,7 +342,6 @@ postgresql_statement_backend::execute(int number)
 
             result_ = PQexec(session_.conn_, query_.c_str());
 #else
-
             if (stType_ == st_repeatable_query)
             {
                 // this query was separately prepared
@@ -404,6 +403,7 @@ postgresql_statement_backend::execute(int number)
     }
     else
     {
+        // releases result_ with PQclear
         throw_postgresql_soci_error(result_);
 
         // dummy, never reach