CODEWITHSUNDEEP
arraysc++11gccvectorc++03
Paradox
Paradox

Reputation: 788

Conversion from array to vector - Interface with C library

I need to use some low-level C functions provided by a library, to wrap them and provide a 'more high-level layer' ; in this case , my problem is to get a data contained within a buffer, and at least to learn how to do it right, I would like to know what you think would be the thing to do in C++03 AND in C++11.

FYI, I am working under Red Hat Linux, with GCC 4.4.7 (so not really C++11-compliant, https://gcc.gnu.org/gcc-4.4/cxx0x_status.html).

Here is a snippet of what I am trying to do :

#define DATA_BLOCKS 4096 // the numbers of 16-bit words within the buffer

std::vector<uint16_t> myClass::getData()
{
    uint16_t buffer[DATA_BLOCKS];
    getDataBuf(fd, dma, am, buffer[]); //C-function provided by the library

    // pushing buffer content into vector
    std::vector <uint16_t> myData;
    for(int i=0; i<DATA_BLOCKS; i++)
         myData.pushback(buffer[i]);
    return myData;
}

Within the link I provided, I am not able to find if it's a good idea to proceed like in C++11 to return the 'whole' vector.

For a vector, is there a best method to fill 'myData' than using the method 'pushback()' within a loop ?

Upvotes: 2

Views: 167

Answers (2)

Thomas
Thomas

Reputation: 5138

data() came with C++11. Using it makes the code more ledgibe in my opinion, and aparently others though so too or it wouldn't have been added.

Upvotes: 1

Garf365
Garf365

Reputation: 3707

You can do that, it's safe :

std::vector<uint16_t> myClass::getData()
{
    std::vector <uint16_t> myData(DATA_BLOCKS);
    getDataBuf(fd, dma, am, myData.data()); //C-function provided by the library
    // Old interface, before c++11 : getDataBuf(fd, dma, am, &myData[0]);

    return myData;
}

or if you want fill given vector:

void myClass::getData(std::vector<uint16_t> &myData)
{
    myData.resize(DATA_BLOCKS);
    getDataBuf(fd, dma, am, myData.data()); //C-function provided by the library
    // Old interface, before c++11 : getDataBuf(fd, dma, am, &myData[0]);
}

Personnally, I have no opinion about returning vector (which will probably use move semantic) or fill a given vector

EDIT

instead of using vector, because you know precisly the size, you can use std::array<std::uint8_t, DATA_BLOCKS> container (new in C++11). This use is same as vector in my examples

EDIT2

vector and array use contiguous storage locations (reference for vector class), so if you get address from first elements, you can access to the second one by incrementing address. The only dangerous point for vector is to be sure to have allocated memory. In both case, I manage to have enough allocated memory : in first example, vector is instanciate with the fill constructor, and in second one I resize vector to corresponding size. This method is describe in the book "Effective STL - 50 Specific Ways to Improve Your Use of the Standard Template Library" [Scott Meyers]. For array, no problem (on condition to declare array with enough memory of course).

Upvotes: 4

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