matlab.io.fits.getHdrSpace

Get number of records in header

Syntax

[nrecs,morekeys] = matlab.io.fits.getHdrSpace(fptr)


Description

[nrecs,morekeys] = matlab.io.fits.getHdrSpace(fptr) returns the number of existing records (not counting the record containing the END keyword) and the amount of space currently available for more keywords. The function returns a value of -1 in the morekeys output argument if the header has not yet been closed.

Note

The CFITSIO library dynamically adds space, if required, when writing new keywords to a header. So, in practice, there is no limit to the number of keywords that you can add to a header.

Examples

Get Available Header Space

import matlab.io.*
fptr = fits.openFile("tst0012.fits");
[nrecs,morekeys] = fits.getHdrSpace(fptr)

nrecs = 
23

morekeys = 
12

fits.closeFile(fptr)

Tips

• This function corresponds to the fits_get_hdrspace (ffghsp) function in the CFITSIO library C API.

• To use this function, you must be familiar with the CFITSIO C interface. You can access the CFITSIO documentation at the CFITSIO website.

Extended Capabilities

Thread-Based Environment

Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool. (since R2026a)

The matlab.io.fits.getHdrSpace function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

Version History

R2026a: Use function in thread-based environments

You can use this function in thread-based environments.