CCfits - HEASARC - NASA

6 Writing Primary Images and Image Extensions 13
extension of type float is also written by calls in between the writes to the primary
header demonstrating switch between HDUs during writes.
Note that in the example below data of type float is written to an image of type unsigned
int, demonstrating both implicit type conversion and the cfitsio extension to unsigned
data.
User keywords can be added to the PHDU after successful construction and these will
both be accessible as container contents in the in-memory FITS object as well as being
written to disk by cfitsio.
Images are represented by the standard library valarray template class which supports
vectorized operations on numeric arrays (e.g. taking the square root of an array) and
slicing techniques.
The code below also illustrates use of C++ standard library algorithms, and the facilities
provided by the std::valarray class.
int writeImage()
{
// Create a FITS primary array containing a 2-D image
// declare axis arrays.
long naxis = 2;
long naxes[2] = { 300, 200 };
// declare auto-pointer to FITS at function scope. Ensures no resources
// leaked if something fails in dynamic allocation.
std::auto_ptr pFits(0);
try
{
// overwrite existing file if the file already exists.
const std::string fileName("!atestfil.fit");
// Create a new FITS object, specifying the data type and axes for the
primary
// image. Simultaneously create the corresponding file.
// this image is unsigned short data, demonstrating the cfitsio
extension
// to the FITS standard.
pFits.reset( new FITS(fileName , USHORT_IMG , naxis , naxes ) );
}
catch (FITS::CantCreate)
{
// ... or not, as the case may be.
return -1;
}
// references for clarity.
long& vectorLength = naxes[0];
long& numberOfRows = naxes[1];
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