Question

I am trying to cast a datastream into a struct since the datastream consists of fixed-width messages and each message has fulle defined fixed width fields as well. I was planning on creating a struct and then using reinterpret_cast to cast pointer to the datastream to the struct to get the fields. I made some test code and get weird results. Could any explain why I am getting these or how to correct the code. (the datastream will be binary and alpha numeric mixed but im just testing with strings)

#pragma pack(push,1)
struct Header 
{
    char msgType[1];
    char filler[1];
    char third[1];
    char fourth[1];
};
#pragma pack(pop)

int main(void)
{
    cout << sizeof(Header) << endl;

    char* data = "four";
    Header* header = reinterpret_cast<Header*>(data);
    cout << header->msgType << endl;
    cout << header ->filler << endl;
    cout << header->third << endl;
    cout << header->fourth << endl;
    return 0;
}

The result that are coming up are

4
four
our
ur
r

I think the four, our and ur is printing since it cant find the null terminator. How do I get around the null terminator issue?

Answer 1

In order to be able to print an array of chars, and being able to distinguish it from a null-terminated string, you need other operator<< definitions:

template< size_t N >
std::ostream& operator<<( std::ostream& out, char (&array)[N] ) {
     for( size_t i = 0; i != N; ++i ) out << array[i];
     return out;
}