How to use vector<string> in OCCI setDataBuffer?

Question

I have a simple table called mytable2 with only one column, name as varchar2(20). I now have a list of names stored as vector of std::string to be inserted into the table. I want to use executeArrayUpdate, so I must do the setDataBuffer first. However, as I could see, people always use char[][20] to set databuffer.

This leaves me a big headache, since I have two issues here, first is to convert from vector to array, second is to convert the string to char.

1st, I tired to use vector of char[20], and this doesn't compile. Googled and they say that vector can't take char[], so I changed my vector of std::string to vector of char*.

2nd, I tried to turn the vector to arrray by using "void* p=&names[0]", as some people say this way we can use vectors just as array.

I used stmt->setDataBuffer(1,mystring,OCCI_SQLT_STR,20,NULL), and the program compiled and executed alright, but when I "select name from mytable2", it showed only some strange charaters.

Anyone has had a similiar issue before? what should I do?

My code is simple as below:

    count=2;
    vector<char*> mystring;
    for(int i=0;i<count;i++)
    {
        char my[20];
        strcpy_s(my,"Michael");
        mystring.insert(mystring.end(),my);
             }
    stmt->setDataBuffer(1,&mystring[0],OCCI_SQLT_STR,20,NULL);

    stmt->setBatchErrorMode (true);

    stmt->executeArrayUpdate(count);

Answer 1

You'd need to dynamically create the char array you're putting into the vector for it to have a chance of working correctly.

I have not used OCCI, but if I had to use API that asked for char[][20], I would give it char[][20]

If you have your existing data in vector, why not just copy it across into the 2D char array? Eg.

// intialise vector with nonsense
unsigned int const VEC_SIZE = 2 ;
vector<string> v;
for (unsigned int i = 0; i < VEC_SIZE; ++i) {
    stringstream s;
    s << "Jon Paul " << i << endl;
    v.push_back ( s.str() ) ;
}

// create the required 2D char array
unsigned int const STR_LEN = 20 ;
char c [VEC_SIZE][STR_LEN];

// copy the data from the vector of strings to the 2D char array
for (unsigned int i = 0; i < VEC_SIZE; ++i) {
    string s = v[i].substr(0,STR_LEN);
    char const * const cc = s.c_str();      
    unsigned int j = 0;
    for (; j < STR_LEN && j < s.size(); ++j) {
        c[i][j] = cc[j];
    }
    c[i][ j==STR_LEN ? 20 : j ] = 0; // write NULL character
}

I take it you've simplified your example to be a fixed size vector, so my response is going to be simplified to, with the thorny issue of dynamic allocation of 2D arrays left as an exercise for the reader...