National Instruments 320682C

Chapter 2 Formatting and I/O Library

Return Value

position long integer Offset of the new file pointer

position from the beginning of

the file.

Return Code

-1 Error due to an invalid file handle, an invalid origin

value, or an offset value that is before the beginning

of the file.

Parameter Discussion

The valid values of origin are as follows:

•0 = beginning of file

•1 = current position of file pointer

•2 = end of file

Using This Function

This function can also be used to obtain the file size by setting offset to 0 and origin to 2. In this

case, the return value indicates the file size and the pointer will be at the end of the file.

It is possible to position the file pointer beyond the end of the file. Intermediate bytes (bytes

between the old end of file and the new end of file) contain indeterminate values. An attempt to

position the file pointer before the beginning of the file causes the function to return an error.

If the file is a device that does not support random access (such as the standard input), the

function returns an indeterminate value.

Example

/* Open or create the file c:\TEST.DAT, move 10 bytes into the

file, and write a string to the file. */

/* Note: Use \\ in pathname in C instead of \. */

int handle,result;

long position;

handle = OpenFile("c:\\TEST.DAT", 0, 2, 1);

if (handle == -1){

FmtOut("error opening file");

exit(1);

}

position = SetFilePtr(handle, 10L, 0);

if (position == 10){