next up previous contents FITSIO Home
Next: 9.2 HDU Access Routines Up: 9. Specialized CFITSIO Interface Previous: 9. Specialized CFITSIO Interface   Contents

9.1 FITS File Access Routines

1
Open an existing FITS file residing in core computer memory. This routine is analogous to fits_open_file. The 'filename' is currently ignored by this routine and may be any arbitrary string. In general, the application must have preallocated an initial block of memory to hold the FITS file prior to calling this routine: 'memptr' points to the starting address and 'memsize' gives the initial size of the block of memory. 'mem_realloc' is a pointer to an optional function that CFITSIO can call to allocate additional memory, if needed (only if mode = READWRITE), and is modeled after the standard C 'realloc' function; a null pointer may be given if the initial allocation of memory is all that will be required (e.g., if the file is opened with mode = READONLY). The 'deltasize' parameter may be used to suggest a minimum amount of additional memory that should be allocated during each call to the memory reallocation function. By default, CFITSIO will reallocate enough additional space to hold the entire currently defined FITS file (as given by the NAXISn keywords) or 1 FITS block (= 2880 bytes), which ever is larger. Values of deltasize less than 2880 will be ignored. Since the memory reallocation operation can be computationally expensive, allocating a larger initial block of memory, and/or specifying a larger deltasize value may help to reduce the number of reallocation calls and make the application program run faster. Note that values of the memptr and memsize pointers will be updated by CFITSIO if the location or size of the FITS file in memory should change as a result of allocating more memory.

  int fits_open_memfile / ffomem
      (fitsfile **fptr, const char *filename, int mode, void **memptr,
       size_t *memsize, size_t deltasize,
       void *(*mem_realloc)(void *p, size_t newsize), int *status)

2
Create a new FITS file residing in core computer memory. This routine is analogous to fits_create_file. In general, the application must have preallocated an initial block of memory to hold the FITS file prior to calling this routine: 'memptr' points to the starting address and 'memsize' gives the initial size of the block of memory. 'mem_realloc' is a pointer to an optional function that CFITSIO can call to allocate additional memory, if needed, and is modeled after the standard C 'realloc' function; a null pointer may be given if the initial allocation of memory is all that will be required. The 'deltasize' parameter may be used to suggest a minimum amount of additional memory that should be allocated during each call to the memory reallocation function. By default, CFITSIO will reallocate enough additional space to hold 1 FITS block (= 2880 bytes) and values of deltasize less than 2880 will be ignored. Since the memory reallocation operation can be computationally expensive, allocating a larger initial block of memory, and/or specifying a larger deltasize value may help to reduce the number of reallocation calls and make the application program run faster. Note that values of the memptr and memsize pointers will be updated by CFITSIO if the location or size of the FITS file in memory should change as a result of allocating more memory.

  int fits_create_memfile / ffimem
      (fitsfile **fptr, void **memptr,
       size_t *memsize, size_t deltasize,
       void *(*mem_realloc)(void *p, size_t newsize), int *status)

3
Reopen a FITS file that was previously opened with fits_open_file or fits_create_file. The new fitsfile pointer may then be treated as a separate file, and one may simultaneously read or write to 2 (or more) different extensions in the same file. The fits_open_file routine (above) automatically detects cases where a previously opened file is being opened again, and then internally call fits_reopen_file, so programs should rarely need to explicitly call this routine.

  int fits_reopen_file / ffreopen
      (fitsfile *openfptr, fitsfile **newfptr, > int *status)

4
Create a new FITS file, using a template file to define its initial size and structure. The template may be another FITS HDU or an ASCII template file. If the input template file name pointer is null, then this routine behaves the same as fits_create_file. The currently supported format of the ASCII template file is described under the fits_parse_template routine (in the general Utilities section)

  int fits_create_template / fftplt
      (fitsfile **fptr, char *filename, char *tpltfile > int *status)

5
Parse the input filename or URL into its component parts, namely: A null pointer (0) may be be specified for any of the output string arguments that are not needed. Null strings will be returned for any components that are not present in the input file name. The calling routine must allocate sufficient memory to hold the returned character strings. Allocating the string lengths equal to FLEN_FILENAME is guaranteed to be safe. These routines are mainly for internal use by other CFITSIO routines.

  int fits_parse_input_url / ffiurl
      (char *filename, > char *filetype, char *infile, char *outfile, char
       *extspec, char *filter, char *binspec, char *colspec, int *status)

  int fits_parse_input_filename / ffifile
      (char *filename, > char *filetype, char *infile, char *outfile, char
       *extspec, char *filter, char *binspec, char *colspec, char *pixspec,
       int *status)

6
Parse the input filename and return the HDU number that would be moved to if the file were opened with fits_open_file. The returned HDU number begins with 1 for the primary array, so for example, if the input filename = `myfile.fits[2]' then hdunum = 3 will be returned. CFITSIO does not open the file to check if the extension actually exists if an extension number is specified. If an extension name is included in the file name specification (e.g. `myfile.fits[EVENTS]' then this routine will have to open the FITS file and look for the position of the named extension, then close file again. This is not possible if the file is being read from the stdin stream, and an error will be returned in this case. If the filename does not specify an explicit extension (e.g. 'myfile.fits') then hdunum = -99 will be returned, which is functionally equivalent to hdunum = 1. This routine is mainly used for backward compatibility in the ftools software package and is not recommended for general use. It is generally better and more efficient to first open the FITS file with fits_open_file, then use fits_get_hdu_num to determine which HDU in the file has been opened, rather than calling fits_parse_input_url followed by a call to fits_open_file.

   int fits_parse_extnum / ffextn
       (char *filename, > int *hdunum, int *status)

7
Parse the input file name and return the root file name. The root name includes the file type if specified, (e.g. 'ftp://' or 'http://') and the full path name, to the extent that it is specified in the input filename. It does not include the HDU name or number, or any filtering specifications. The calling routine must allocate sufficient memory to hold the returned rootname character string. Allocating the length equal to FLEN_FILENAME is guaranteed to be safe.

   int fits_parse_rootname / ffrtnm
       (char *filename, > char *rootname, int *status);

8
Test if the input file or a compressed version of the file (with a .gz, .Z, .z, or .zip extension) exists on disk. The returned value of the 'exists' parameter will have 1 of the 4 following values:

   2:  the file does not exist, but a compressed version does exist
   1:  the disk file does exist
   0:  neither the file nor a compressed version of the file exist
  -1:  the input file name is not a disk file (could be a ftp, http,
       smem, or mem file, or a file piped in on the STDIN stream)

   int fits_file_exists / ffexist
       (char *filename, > int *exists, int *status);

9
Flush any internal buffers of data to the output FITS file. These routines rarely need to be called, but can be useful in cases where other processes need to access the same FITS file in real time, either on disk or in memory. These routines also help to ensure that if the application program subsequently aborts then the FITS file will have been closed properly. The first routine, fits_flush_file is more rigorous and completely closes, then reopens, the current HDU, before flushing the internal buffers, thus ensuring that the output FITS file is identical to what would be produced if the FITS was closed at that point (i.e., with a call to fits_close_file). The second routine, fits_flush_buffer simply flushes the internal CFITSIO buffers of data to the output FITS file, without updating and closing the current HDU. This is much faster, but there may be circumstances where the flushed file does not completely reflect the final state of the file as it will exist when the file is actually closed.

A typical use of these routines would be to flush the state of a FITS table to disk after each row of the table is written. It is recommend that fits_flush_file be called after the first row is written, then fits_flush_buffer may be called after each subsequent row is written. Note that this latter routine will not automatically update the NAXIS2 keyword which records the number of rows of data in the table, so this keyword must be explicitly updated by the application program after each row is written.

  int fits_flush_file / ffflus
      (fitsfile *fptr, > int *status)

  int fits_flush_buffer / ffflsh
      (fitsfile *fptr, 0, > int *status)

      (Note:  The second argument must be 0).


next up previous contents FITSIO Home
Next: 9.2 HDU Access Routines Up: 9. Specialized CFITSIO Interface Previous: 9. Specialized CFITSIO Interface   Contents