The readData flag is by default false (see below for the alternative case), which means that the data in the column is not read.
int readHeader() { const string SPECTRUM("SPECTRUM"); // read a particular HDU within the file. This call reads just the header // information from SPECTRUM std::auto_ptr<FITS> pInfile(new FITS("file1.pha",Read,SPECTRUM)); // define a reference for clarity. (std::auto_ptr<T>::get returns a pointer ExtHDU& table = pInfile->extension(SPECTRUM); // read all the keywords, excluding those associated with columns. table.readAllKeys(); // print the result. std::cout << table << std::endl; return 0; }