[C++] stringop-overflow warning in generateConstPropertyMethods output

[neomantra]

While building SBE-generated C++ code for <group> fields, I see the following compiler warning for code generated from Group->Field elements with a char primitive type:

warning: 'strlen' argument missing terminating nul [-Wstringop-overflow=]

The generated code block looks like this:

class MDIncrementalRefreshTradeSummary42
{
	.....
    class NoMDEntries
    {
        .....
        SBE_NODISCARD const char *mDEntryType() const
        {
            static const std::uint8_t mDEntryTypeValues[] = { 50 };

            return (const char *)mDEntryTypeValues;
        }

Inspecting the situation, I see that:

• SBE-message end-users should use length functions like mDEntryTypeLength()
• The return value of mDEntryType() truly a pointer to a single char, not a NULL-terminated string.

So in that regard, this is not a SBE codegen bug. But, unfortunately any C++ programmer can pass that const char* to a myriad of functions that expect the input to be NULL terminated. This could lead to inadvertent out-of-bounds / buffer-overrun bugs.

Adding a NULL to the static array in that function would mitigate this class of bugs at small expense of static storage. So something like this at this line:

-            indent + "        static const std::uint8_t %1$sValues[] = { %2$s };\n\n" +
+            indent + "        static const std::uint8_t %1$sValues[] = { %2$s, 0 };\n\n" +

While I'm here, I'd also like to thank you for all your fantastic contributions and thought leadership to both software engineering at-large and particularly in the trading community. 🤗

[mjpt777]

Can you post the snippet of the schema for the field?

[neomantra]

It is the MDEntryType field of NoGroupEntries group of MDIncrementalRefreshTradeSummary42 messages from this
CME schema:

ftp://ftp.cmegroup.com/SBEFix/Production/Templates/templates_FixBinary.xml

    <ns2:message name="MDIncrementalRefreshTradeSummary42" id="42" description="MDIncrementalRefreshTradeSummary" blockLength="11" semanticType="X" sinceVersion="5">
        <field name="TransactTime" id="60" type="uInt64" description="Start of event processing time in number of nanoseconds since Unix epoch" offset="0" semanticType="UTCTimestamp"/>
        <field name="MatchEventIndicator" id="5799" type="MatchEventIndicator" description="Bitmap field of eight Boolean type indicators reflecting the end of updates for a given Globex event" offset="8" semanticType="MultipleCharValue"/>
        <group name="NoMDEntries" id="268" description="Number of Trade Summary entries" blockLength="32" dimensionType="groupSize">
            <field name="MDEntryPx" id="270" type="PRICE" description="Trade price" offset="0" semanticType="Price"/>
            <field name="MDEntrySize" id="271" type="Int32" description="Consolidated trade quantity" offset="8" semanticType="Qty"/>
            <field name="SecurityID" id="48" type="Int32" description="Security ID as defined by CME" offset="12" semanticType="int"/>
            <field name="RptSeq" id="83" type="uInt32" description="Sequence number per instrument update" offset="16" semanticType="int"/>
            <field name="NumberOfOrders" id="346" type="Int32NULL" description="The total number of real orders per instrument that participated in a match step within a match event" offset="20" semanticType="int"/>
            <field name="AggressorSide" id="5797" type="AggressorSide" description="Indicates which side is the aggressor or if there is no aggressor" offset="24" semanticType="int"/>
            <field name="MDUpdateAction" id="279" type="MDUpdateAction" description="Market Data update action" offset="25" semanticType="int"/>
            <field name="MDEntryType" id="269" type="MDEntryTypeTrade" description="Market Data entry type" semanticType="char"/>
            <field name="MDTradeEntryID" id="37711" type="uInt32NULL" description="Market Data Trade entry ID" offset="26" sinceVersion="7" semanticType="int"/>
        </group>
        <group name="NoOrderIDEntries" id="37705" description="Number of OrderID entries" blockLength="16" dimensionType="groupSize8Byte">
            <field name="OrderID" id="37" type="uInt64" description="Unique order identifier as assigned by the exchange" offset="0" semanticType="int"/>
            <field name="LastQty" id="32" type="Int32" description="Quantity bought or sold on this last fill" offset="8" semanticType="Qty"/>
        </group>
    </ns2:message>

[mjpt777]

For constant values I can kind of see a point here. However this issue would exist regardless for required values if the user filled all values of the array with chars and did not put in a null termination. Adding the null terminator like you suggest might be the safest way to go.