xdf_read man page

xdf_read — Read samples from a xDF file

Synopsis

#include <xdfio.h>

int xdf_read(struct xdf* xdf, unsigned int ns, ...);

Description

xdf_read() reads ns samples from the xDF file referenced by xdf. This file should have been opened with mode XDF_READ and xdf_prepare_arrays(3) should have been successfully called on it. xdf_read() will fail otherwise).

The data to be read will be transferred into arrays specified by pointers provided in the variable list of arguments of the function. The function expects the same number of arrays as specified by previous call to xdf_define_arrays(3). The internal organisation of the data in the arrays should have been specified previously with calls to xdf_set_chconf(3).

In addition, it is important to note that none of the arrays should overlap.

Return Value

The function returns the number of the samples successfully read from the xDF file in case of success. The number of samples read can be smaller than the number requested in the end of the file is reached. In case of error, -1 is returned and errno is set appropriately.

Errors

EINVAL
xdf is NULL
EPERM
No successfull call to xdf_prepare_transfer(3) have been done on xdf or it has been opened using the mode XDF_WRITE.
EINTR
The call was interrupted by a signal before any data was written; see signal(7).
EIO
A low-level I/O error occurred while reading from the inode.
ESTALE
Stale file handle. This error can occur for NFS and for other file systems

Example

/* Assume xdf references a xDF file opened for reading whose
channels source their data in 2 arrays of float whose strides
are the length of respectively 4 and 6 float values,
i.e. 16 and 24 bytes (in most platforms)*/
#define NS    3
float array1[NS][4], array2[NS][6];
unsigned int strides = {4*sizeof(float), 6*sizeof(float)};
unsigned int i;

xdf_define_arrays(xdf, 2, strides);
if (xdf_prepare_transfer(xdf))
	return 1;

for (i=0; i<45; i+=NS) {
	/* Write the values to the file */
        if (xdf_write(xdf, NS, array1, array2))
		return 1;

	/* Use the values contained in array1 and array2*/
	...

}

xdf_close(xdf);

See Also

xdf_set_chconf(3), xdf_define_arrays(3), xdf_prepare_transfer(3)

Referenced By

xdf_define_arrays(3), xdf_prepare_transfer(3).

2010 EPFL xdffileio library manual