La cosa più semplice per capire come funziona è guardare il listato.
Le funzioni sono in Stream.cpp
// returns the first valid (long) integer value from the current position.
// initial characters that are not digits (or the minus sign) are skipped
// function is terminated by the first character that is not a digit.
long Stream::parseInt()
{
return parseInt(NO_SKIP_CHAR); // terminate on first non-digit character (or timeout)
}
// as above but a given skipChar is ignored
// this allows format characters (typically commas) in values to be ignored
long Stream::parseInt(char skipChar)
{
boolean isNegative = false;
long value = 0;
int c;
c = peekNextDigit();
// ignore non numeric leading characters
if(c < 0)
return 0; // zero returned if timeout
do{
if(c == skipChar)
; // ignore this charactor
else if(c == '-')
isNegative = true;
else if(c >= '0' && c <= '9') // is c a digit?
value = value * 10 + c - '0';
read(); // consume the character we got with peek
c = timedPeek();
}
while( (c >= '0' && c <= '9') || c == skipChar );
if(isNegative)
value = -value;
return value;
}
// as parseInt but returns a floating point value
float Stream::parseFloat()
{
return parseFloat(NO_SKIP_CHAR);
}
// as above but the given skipChar is ignored
// this allows format characters (typically commas) in values to be ignored
float Stream::parseFloat(char skipChar){
boolean isNegative = false;
boolean isFraction = false;
long value = 0;
char c;
float fraction = 1.0;
c = peekNextDigit();
// ignore non numeric leading characters
if(c < 0)
return 0; // zero returned if timeout
do{
if(c == skipChar)
; // ignore
else if(c == '-')
isNegative = true;
else if (c == '.')
isFraction = true;
else if(c >= '0' && c <= '9') { // is c a digit?
value = value * 10 + c - '0';
if(isFraction)
fraction *= 0.1;
}
read(); // consume the character we got with peek
c = timedPeek();
}
while( (c >= '0' && c <= '9') || c == '.' || c == skipChar );
if(isNegative)
value = -value;
if(isFraction)
return value * fraction;
else
return value;
}
Le funzioni usano due metodi privati della classe per leggere il carattere successivo.
// private method to peek stream with timeout
int Stream::timedPeek()
{
int c;
_startMillis = millis();
do {
c = peek();
if (c >= 0) return c;
} while(millis() - _startMillis < _timeout);
return -1; // -1 indicates timeout
}
// returns peek of the next digit in the stream or -1 if timeout
// discards non-numeric characters
int Stream::peekNextDigit()
{
int c;
while (1) {
c = timedPeek();
if (c < 0) return c; // timeout
if (c == '-') return c;
if (c >= '0' && c <= '9') return c;
read(); // discard non-numeric
}
}
Read, Peek e Flush sono dichiarate virtuali e si riferiscono alla classe chiamante la classe Stream, ad esempio Serial.
virtual int read() = 0;
virtual int peek() = 0;
virtual void flush() = 0;
Quindi il read() può essere interpretato come Serial.read(), cioè legge un carattere dalla Seriale.