Programming in C

476 Appendix B The Standard C Library
associated with filePtr. If the freopen call is successful, filePtr is returned; otherwise,
a null pointer is returned.The freopen function is frequently used to reassign
stdin, stdout, or stderr in the program. For example, the call
if ( freopen ("inputData", "r", stdin) == NULL ) {
...
}
has the effect of reassigning stdin to the file inputData, which is opened in read
access mode. Subsequent I/O operations performed with stdin are performed with
the file inputData, as if stdin had been redirected to this file when the program was
executed.
int fscanf (filePtr, format, arg1, arg2, ..., argn)
Reads data items from the file identified by filePtr, according to the format specified
by the character string format.The values that are read are stored in the arguments
specified after format, each of which must be a pointer.The format characters
that are allowed in format are the same as those for the scanf function (see Chapter
16).The fscanf function returns the number of items successfully read and assigned
(excluding any %n assignments) or the value EOF if the end of file is reached before
the first item is converted.
int fseek (filePtr, offset, mode)
Positions the indicated file to a point that is offset (a long int) bytes from the
beginning of the file, from the current position in the file, or from the end of the file,
depending upon the value of mode (an integer). If mode equals SEEK_SET, positioning
is relative to the beginning of the file. If mode equals SEEK_CUR, positioning is relative
to the current position in the file. If mode equals SEEK_END, positioning is relative to
the end of the file. SEEK_SET, SEEK_CUR,and SEEK_END are defined in .
On systems that distinguish between text and binary files, SEEK_END might not be
supported for binary files. For text files, either offset must be zero or must be a
value returned from a prior call to ftell. In the latter case, mode must be SEEK_SET.
If the fseek call is unsuccessful, a nonzero value is returned.
int fsetpos (filePtr, fpos)
Sets the current file position for the file associated with filePtr to the value pointed
to by fpos, which is of type fpos_t (defined in ). Returns zero on success,
and nonzero on failure. See also fgetpos.
long ftell (filePtr)
Returns the relative offset in bytes of the current position in the file identified by
filePtr, or –1L on error.