The CFITSIO routines that read and write numerical data can perform implicit data type conversion. This means that the data type of the variable or array in the program does not need to be the same as the data type of the value in the FITS file. Data type conversion is supported for numerical and string data types (if the string contains a valid number enclosed in quotes) when reading a FITS header keyword value and for numeric values when reading or writing values in the primary array or a table column. CFITSIO returns status = NUM_OVERFLOW if the converted data value exceeds the range of the output data type. Implicit data type conversion is not supported within binary tables for string, logical, complex, or double complex data types.
In addition, any table column may be read as if it contained string values. In the case of numeric columns the returned string will be formated using the TDISPn display format if it exists.