read method
Reads characters into an array.
This method will block until some input is available, an I/O error occurs, or the end of the stream is reached.
Parameters
cbuf
: Destination bufferoffset
: Offset at which to start storing characters (default: 0)length
: Maximum number of characters to read (default: remaining buffer space)
Returns
The number of characters read, or -1 if the end of the stream has been reached.
Example
final reader = FileReader('text.txt');
try {
final buffer = List<int>.filled(1024, 0);
final charsRead = await reader.read(buffer);
if (charsRead != -1) {
final text = String.fromCharCodes(buffer.sublist(0, charsRead));
print('Read: $text');
}
} finally {
await reader.close();
}
Throws InvalidArgumentException if offset
or length
is negative, or if
offset
+ length
is greater than the length of cbuf
.
Throws IOException if an I/O error occurs.
Throws StreamClosedException if the reader has been closed.
Implementation
@override
Future<int> read(List<int> cbuf, [int offset = 0, int? length]) async {
length ??= cbuf.length - offset;
if (offset < 0 || length < 0 || offset + length > cbuf.length) {
throw InvalidArgumentException('Invalid offset or length');
}
if (length == 0) {
return 0;
}
await _ensureOpen();
if (_buffer == null || _bufferPosition >= _buffer!.length) {
return -1; // End of file
}
final availableChars = _buffer!.length - _bufferPosition;
final charsToRead = length.clamp(0, availableChars);
for (int i = 0; i < charsToRead; i++) {
cbuf[offset + i] = _buffer!.codeUnitAt(_bufferPosition + i);
}
_bufferPosition += charsToRead;
return charsToRead;
}