For A-Format input conversion, w must be specified (unless the A-Format is used to read a variable-length line, as explained below). The result is a character string containing the next w characters from the input stream file.
The A-Format is used without a field width to read a variable-length line. The A-Format reads the content of the current line, starting with the current column and ending with the end of the line, then sets the column position so that the next operation will read a new line.