Node:File Positioning, Previous:EOF and Errors, Up:C-Style I/O Functions
Three functions are available for setting and determining the position of the file pointer for a given file.
| ftell (fid) | Built-in Function |
| Return the position of the file pointer as the number of characters from the beginning of the file fid. |
| fseek (fid, offset, origin) | Built-in Function |
|
Set the file pointer to any location within the file fid.
The pointer is positioned offset characters from the origin,
which may be one of the predefined variables Return 0 on success and -1 on error. |
| SEEK_SET | Built-in Variable |
| SEEK_CUR | Built-in Variable |
| SEEK_END | Built-in Variable |
These variables may be used as the optional third argument for the
function fseek.
|
| frewind (fid) | Built-in Function |
Move the file pointer to the beginning of the file fid, returning
0 for success, and -1 if an error was encountered. It is equivalent to
fseek (fid, 0, SEEK_SET).
|
The following example stores the current file position in the variable
marker, moves the pointer to the beginning of the file, reads
four characters, and then returns to the original position.
marker = ftell (myfile); frewind (myfile); fourch = fgets (myfile, 4); fseek (myfile, marker, SEEK_SET);