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c++arduinoesp8266arduino-esp8266platformio

Read from serial data length is always 1

Trying to read bytes from serial to buffer:

char buf[512];
if (int len = Serial.readBytes(buf, 512) > 0)
{
   DEBUG_LOGF("got bytes available=%d", len);
}else
{
   DEBUG_LOG("nothing read");
}

I'm always get 1 in len even it send data was long string. Strange thing is I found whole long string data in buf, while I still have len==1.

Why? How to fix that?

Solution

  • It's because of operator precedence.

    The expression int len = Serial.readBytes(buf, 512) > 0 is really equal to int len = (Serial.readBytes(buf, 512) > 0).

    That is, you assign the result of the comparison Serial.readBytes(buf, 512) > 0 to the variable len.

    You need to split the variable definition and the assignment to it, and use parentheses to get the correct precedence:

    char buf[512];
int len;
if ((len = Serial.readBytes(buf, 512)) > 0)