Add SOCI_DUMMY_INIT() macro and use it

This allows to clearly indicate the initializations done just to avoid
compiler warnings instead of having to write an ad hoc comment in every
place where this was done.

No real changes.

Author: vadz

include/soci/soci-platform.h

@@ -144,6 +144,14 @@ namespace cxx_details
 
 #define SOCI_UNUSED(x) (void)x;
 
+// This macro can be used to avoid warnings from MSVC (and sometimes from gcc,
+// if initialization is indirect) about "uninitialized" variables that are
+// actually always initialized. Using this macro makes it clear that the
+// initialization is only necessary to avoid compiler warnings and also will
+// allow us to define it as doing nothing if we ever use a compiler warning
+// about initializing variables unnecessarily.
+#define SOCI_DUMMY_INIT(x) (x)
+
 #if defined(SOCI_HAVE_CXX11) || (defined(_MSC_VER) && _MSC_VER >= 1900)
     #define SOCI_NOEXCEPT noexcept
     #define SOCI_NOEXCEPT_FALSE noexcept(false)

src/backends/db2/vector-into-type.cpp

@@ -34,7 +34,7 @@ void db2_vector_into_type_backend::define_by_pos(
     this->data = data; // for future reference
     this->type = type; // for future reference
 
-    SQLINTEGER size = 0;       // also dummy
+    SQLINTEGER size SOCI_DUMMY_INIT(0);
 
     switch (type)
     {
@@ -344,7 +344,7 @@ void db2_vector_into_type_backend::resize(std::size_t sz)
 
 std::size_t db2_vector_into_type_backend::size()
 {
-    std::size_t sz = 0; // dummy initialization to please the compiler
+    std::size_t sz SOCI_DUMMY_INIT(0);
     switch (type)
     {
     // simple cases

src/backends/db2/vector-use-type.cpp

@@ -322,7 +322,7 @@ void db2_vector_use_type_backend::pre_use(indicator const *ind)
 
 std::size_t db2_vector_use_type_backend::size()
 {
-    std::size_t sz = 0; // dummy initialization to please the compiler
+    std::size_t sz SOCI_DUMMY_INIT(0);
     switch (type)
     {
     // simple cases

src/backends/mysql/vector-into-type.cpp

@@ -199,7 +199,7 @@ void mysql_vector_into_type_backend::resize(std::size_t sz)
 
 std::size_t mysql_vector_into_type_backend::size()
 {
-    std::size_t sz = 0; // dummy initialization to please the compiler
+    std::size_t sz SOCI_DUMMY_INIT(0);
     switch (type_)
     {
         // simple cases

src/backends/mysql/vector-use-type.cpp

@@ -185,7 +185,7 @@ void mysql_vector_use_type_backend::pre_use(indicator const *ind)
 
 std::size_t mysql_vector_use_type_backend::size()
 {
-    std::size_t sz = 0; // dummy initialization to please the compiler
+    std::size_t sz SOCI_DUMMY_INIT(0);
     switch (type_)
     {
         // simple cases

src/backends/odbc/statement.cpp

@@ -249,7 +249,7 @@ odbc_statement_backend::fetch(int number)
 
     SQLSetStmtAttr(hstmt_, SQL_ATTR_ROW_BIND_TYPE, SQL_BIND_BY_COLUMN, 0);
 
-    statement_backend::exec_fetch_result res = ef_success; // just for MSVC
+    statement_backend::exec_fetch_result res SOCI_DUMMY_INIT(ef_success);
 
     // Usually we try to fetch the entire vector at once, but if some into
     // string columns are bigger than 8KB (ODBC_MAX_COL_SIZE) then we use

src/backends/oracle/standard-into-type.cpp

@@ -60,8 +60,8 @@ void oracle_standard_into_type_backend::define_by_pos(
     data_ = data; // for future reference
     type_ = type; // for future reference
 
-    ub2 oracleType = 0; // dummy initialization to please the compiler
-    sb4 size = 0;       // also dummy
+    ub2 oracleType SOCI_DUMMY_INIT(0);
+    sb4 size SOCI_DUMMY_INIT(0);
 
     switch (type)
     {

src/backends/oracle/vector-into-type.cpp

@@ -52,8 +52,8 @@ void oracle_vector_into_type_backend::define_by_pos_bulk(
 
     end_var_ = full_size();
 
-    ub2 oracleType = 0;  // dummy initialization to please the compiler
-    sb4 elementSize = 0; // also dummy
+    ub2 oracleType SOCI_DUMMY_INIT(0);
+    sb4 elementSize SOCI_DUMMY_INIT(0);
     void * dataBuf = NULL;
 
     switch (type)

src/backends/postgresql/vector-into-type.cpp

@@ -260,7 +260,7 @@ std::size_t postgresql_vector_into_type_backend::size()
 
 std::size_t postgresql_vector_into_type_backend::full_size()
 {
-    std::size_t sz = 0; // dummy initialization to please the compiler
+    std::size_t sz SOCI_DUMMY_INIT(0);
     switch (type_)
     {
         // simple cases

src/backends/postgresql/vector-use-type.cpp

@@ -237,7 +237,7 @@ std::size_t postgresql_vector_use_type_backend::size()
 
 std::size_t postgresql_vector_use_type_backend::full_size()
 {
-    std::size_t sz = 0; // dummy initialization to please the compiler
+    std::size_t sz SOCI_DUMMY_INIT(0);
     switch (type_)
     {
         // simple cases