Question

I have code that works on Windows, but now that I am porting to a MAC, using Xcode 3.2.5 C/C++ Compiler Version GCC 4.2, it crashes.

I have narrowed it down to a memset call. If I comment out the memset it works, and if I put it back in the code crashes.

I have a structure that looks like this in my header file:

typedef struct 
{
    int deviceCount;
    struct 
    {
        #define MAX_DEVICE_ID 256
        #define MAX_DEVICE_ENTRIES 10
        std::string deviceId;   // Device name to Open
        TransportType   eTransportType;
    } deviceNodes[MAX_DEVICE_ENTRIES];
} DeviceParams;

Then in a cpp file I have this:

DeviceParams Param;
memset(&Param, nil, sizeof(Param));

… later I have this:

pParam->deviceNodes[index].deviceId = "some string"; // <----- Line that crashes with memset

Like I said before if I remove the memset call everything works fine. If I look at the debugger before I call the memset my strings in the structure are \0 and after the memset they are nil.

Why does the nil string crash on a assignment line and only on a MAC?

Thanks.

Answer 1

You’re overwriting deviceId‘s internal data by doing memset all over it; don’t ever do memset over anything but a POD data type. This is C++, we have constructors. Your code should look something like this:

struct DeviceParams
{
    int deviceCount;

    struct DeviceNode
    {
        DeviceNode() : eTransportType() { } // initialise eTransportType
                                            // to 0, deviceId initialises itself

        static const int MAX_DEVICE_ID = 256;
        static const int MAX_DEVICE_ENTRIES = 10;

        std::string deviceId; // Device name to Open
        TransportType eTransportType;
    } deviceNodes[DeviceNode::MAX_DEVICE_ENTRIES];
};

Then

DeviceParams Param;

// get a pointer to Param in pParam

pParam->deviceNodes[index].deviceId = "some string";