Maximum string length of 13 characters about arduinojson HOT 2 CLOSED

Hi @DWilhelmLKKS,

I was about to tell you the same thing :-)
Indeed, printf() is a legacy of the C language and knows nothing about String and classes in general.
I don't know why they decided to integrate it into ESP32's core.

BTW, it was accidentally working with strings of 13 characters or less because of the short-string optimization (SSO) implemented in ESP32's String:

struct _ptr { 
    char *   buff;
    uint32_t cap;
    uint32_t len;
};
enum { SSOSIZE = sizeof(struct _ptr) + 4 - 1 };
struct _sso {
    char     buff[SSOSIZE];
    unsigned char len   : 7;
    unsigned char isSSO: 1;
};

This gives an SSOSIZE of 12 + 4 - 1 = 15, enough room for 14 characters and the terminator.
So, in theory, 14-character strings should have worked too, but there is an off-by-one error in the length comparison that decides whether to use SSO or not:

if (maxStrLen < sizeof(sso.buff) - 1)

It should be <= instead of <; that's why SSO doesn't work with 14-character strings.

Best regard,
Benoit

from arduinojson.

I found the solution! It had nothing to do with ArduinoJson. :)
Using this code fixed it:

Serial.printf("%s / %s / %s\n", remotesList[i-1].link.c_str(), remotesList[i-1].manufacturer.c_str(), remotesList[i-1].serial.c_str());

from arduinojson.