Help understanding structure behaviior in esp now example

Projects Programming
24

here's a memory dump of the contents of struct struct_message, renamed Msg

both 'a', the c-string and 'e', the String have the same values, "Some String". you can see the matching ASCII values 'a' contains, but 'e' contains just 6 values which aren't printable ASCII values

dump: msg
 53 6f 6d 65 20 53 74 72
 69 6e 67 00 00 00 00 00
 00 00 00 00 00 00 00 00
 00 00 00 00 00 00 00 00
 ad 7e 00 00 80 3f d4 02
 0b 00 0b 00 01

dump: msg.a - char[]
 53 6f 6d 65 20 53 74 72
 69 6e 67 00 00 00 00 00
 00 00 00 00 00 00 00 00
 00 00 00 00 00 00 00 00

dump: msg.b - int
 ad 7e

dump: msg.c - float
 00 00 80 3f

dump: msg.d - String
 d4 02 0b 00 0b 00

dump: msg.e - bool
 01

  1 sizoef char
  2 sizoef int
  4 sizoef float
  6 sizoef String
  1 sizoef bool



struct Msg {
  char   a[32];
  int    b;
  float  c;
  String d;
  bool   e;
};

Msg msg = { "Some String", 0x7ead, 1.0, "Some String", 1 };


char s [90];

// -----------------------------------------------------------------------------
void
dump (
    uint8_t    *p,
    unsigned    nByte,
    const char *label )
{
    sprintf (s, "dump: %s", label);
    Serial.print (s);
    for (unsigned n = 0; n < nByte; n++) {
        if (! (n % 8))
            Serial.println ();
        sprintf (s, " %02x", *p++);
        Serial.print (s);
    }
    Serial.println ();
    Serial.println ();
}

// -----------------------------------------------------------------------------

void
dumpMsg (
    Msg msg )
{
    dump ((uint8_t*) & msg, sizeof(msg),      "msg");
    dump ((uint8_t*) & msg.a, 32,             "msg.a - char[]");
    dump ((uint8_t*) & msg.b, sizeof(int),    "msg.b - int");
    dump ((uint8_t*) & msg.c, sizeof(float),  "msg.c - float");
    dump ((uint8_t*) & msg.d, sizeof(String), "msg.d - String");
    dump ((uint8_t*) & msg.e, sizeof(bool),   "msg.e - bool");
}

// -----------------------------------------------------------------------------
void
setup (void)
{
    Serial.begin (9600);

    dumpMsg (msg);

    sprintf (s, " %2d sizoef %s", sizeof(char), "char");    Serial.println (s);
    sprintf (s, " %2d sizoef %s", sizeof(int), "int");      Serial.println (s);
    sprintf (s, " %2d sizoef %s", sizeof(float), "float");  Serial.println (s);
    sprintf (s, " %2d sizoef %s", sizeof(String), "String");Serial.println (s);
    sprintf (s, " %2d sizoef %s", sizeof(bool), "bool");    Serial.println (s);
}

void
loop (void)
{
}