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);