Trying to copy char array to struct crashing - c

Question

(to preface this my C is terrible)
I'm trying to send a string from iOS to a BLE device. I encode the string in swift and write it like this:
func sendUserName(userName: String) {
let bytes: [UInt8] = Array(userName.utf8)
print(bytes.count)
let data = NSData(bytes: bytes, length: bytes.count)
capsenseLedBoard!.writeValue(data, forCharacteristic: userIdCharacteristic, type: CBCharacteristicWriteType.WithResponse)
}
I send in this string "THISISATEST123456789" and this line print(bytes.count) prints out 20.
I recieve the data on the BLE device like this and pass it to the below userDidConnect function:
userDidConnect((char *)wrReqParam->handleValPair.value.val);
I have a struct called Event that looks like this:
struct Event {
char time[20]; // The time in ISO 1601 format
char name[3]; // The two character name of the event. See header for declarations.
char userId[20]; // The userId of the connected user if one is present.
struct Event* next;
};
I have a global variable declared like this:
char currentlyConnectedUserID[20];
I then have an enqueue function that looks like this:
/**
Creates a new Event and adds to the linked list.
#param time The time in ISO 8601 format.
#param name The name descriptor of the event ("VS", "VO", etc.)
#param userId The id of the user who is currently connect (if they are connected).
*/
void enqueueEvent(char time[20], char name[3], char userId[20]) {
struct Event* temp = (struct Event*)malloc(sizeof(struct Event));
strncpy( temp->time, time, 20);
strncpy( temp->name, name, 3);
strncpy( temp->userId, userId, 20);
temp->next = NULL;
if(front == NULL && rear == NULL) {
front = rear = temp;
return;
}
rear->next = temp;
rear = temp;
}
I have a function that accepts a new userId and then creates a new Event off of it and adds it to the linked list..well this is what it's suppose to do:
void userDidConnect(char *userId)
{
size_t destination_size = sizeof(userId);
snprintf(currentlyConnectedUserID, destination_size, "%s", userId);
//enqueueEvent("2007-03-01T13:00:20", "UC", currentlyConnectedUserID);
showMessageInUART(currentlyConnectedUserID, sizeof(currentlyConnectedUserID));
}
Currently if I run the userDidConnect method above I'm able to printout the currentlyConnectedUserID properly. However, if I uncomment out this line:
//enqueueEvent("2007-03-01T13:00:20", "UC", currentlyConnectedUserID);
I get a "crash". I'm doing this in a fairly obscure IDE (PSoC Creator from Cypress) so I don't see any error logs or IDE crash logs. The only way I can tell is that the showMessageInUART is never called, so I know it has to be that line.
I'm able to successfully create and enqueue a new Event if I do this:
enqueueEvent("2007-03-01T13:00:20", "UC", "1234567891234567891");
My only thought is that maybe the size of the array is wrong? Maybe? Or perhaps there is some trailing \0 that is screwing things up?
Suggestion updates:
I've tried doing this:
size_t destination_size = strlen(userId) + 1;
Which gives the correct value into currentlyConnectedUserID however enqueueing still causes a crash.
--
I've replaced strcpy with strncpy which is still causing a crash ;(
--
Tried this to ensure I didn't overflow which still didn't work:
sprintf(currentlyConnectedUserID, "%.19s", userId);
UPDATE
I updated my enqueue to look like this since don't have breakpoints:
void enqueueEvent(char time[20], char name[3], char userId[20]) {
UART_UartPutString("start enqueue");
struct Event* temp = (struct Event*)malloc(sizeof(struct Event));
UART_UartPutString("1");
strncpy( temp->time, time, 20);
UART_UartPutString("2");
strncpy( temp->name, name, 3);
UART_UartPutString("3");
strncpy( temp->userId, userId, 20);
UART_UartPutString("4");
temp->next = NULL;
UART_UartPutString("5");
if(front == NULL && rear == NULL) {
front = rear = temp;
return;
}
rear->next = temp;
rear = temp;
}
This line is crashing:
strncpy( temp->time, time, 20);
aka we never make it here: UART_UartPutString("2");
If I call this same function from main it works fine. Any idea why it would be crashing here when called from a different method?

Answer 1

The strcpy funtion Copies the C string pointed by source into the array pointed by destination, including the terminating null character (and stopping at that point).
Therefore, I propose you to change the enqueueEvent funtion, using strncpy instead of dangerous strcpy as :
void enqueueEvent(char time[20], char name[3], char userId[20]) {
struct Event* temp = (struct Event*)malloc(sizeof(struct Event));
strncpy( temp->time, time,20);
strncpy( temp->name, name,3);
strncpy( temp->userId, userId,20);
temp->next = NULL;
if(front == NULL && rear == NULL) {
front = rear = temp;
return;
}
rear->next = temp;
rear = temp;
}
Change also the allocation of temp pointer from local stack of the enqueueEvent function to global level because the pointer allocation is vanished when going outside of the function.