NAME¶
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)
