C++ stops connecting to DB after so many successful connects - c++

Question

I am currently using C++ to write directly to a mySQL database, the program will write the first 151 items in the data base but as soon as it gets to number 152 it fails to connect to the data base and throws this exact error:
Unhandled exception at 0x6188F1F9 (libmysql.dll) in Project1.exe: 0xC0000005: Access violation reading location 0x000003B0
I have no idea what this means and cannot seem to find anything on the internet about it. Below I will post the code that writes to the DB. Again though I will say that it is working just fine up until number 152.
void writeToDB(string coordString, string time, string id){
MYSQL *connect; // Create a pointer to the MySQL instance
connect=mysql_init(NULL); // Initialise the instance
/* This If is irrelevant and you don't need to show it. I kept it in for Fault Testing.*/
if(!connect) /* If instance didn't initialize say so and exit with fault.*/
{
fprintf(stderr,"MySQL Initialization Failed");
}
/* Now we will actually connect to the specific database.*/
connect=mysql_real_connect(connect,SERVER,USER,PASSWORD,DATABASE,0,NULL,0);
/* Following if statements are unneeded too, but it's worth it to show on your
first app, so that if your database is empty or the query didn't return anything it
will at least let you know that the connection to the mysql server was established. */
if(connect){
printf("Connection Succeeded\n");
}
else{
printf("Connection Failed!\n");
return;
}
MYSQL_RES *result; /* Create a pointer to recieve the return value.*/
MYSQL_ROW row; /* Assign variable for rows. */
std::string strSql = "INSERT INTO locationtime (id, dateTime, location) VALUES ('" + id + "','" + time + "','" + coordString + "')";;
const char* sql = strSql.c_str();
mysql_query(connect, sql);
/* Send a query to the database. */
mysql_close(connect); /* Close and shutdown */
}
EDIT: Okay so I was able to get it to stop throwing the error, however it is still just mysteriously refusing to connect to the DB, I did test it with a PHP script instead and got 800+ values in the table with no issue at all. Im not sure what the issue is at all!

Answer 1

If the mysql_real_connect() had failed you should also put a return; or exit(1) after the printf("Connection Failed!\n");:
if(connect) {
printf("Connection Succeeded\n");
}
else {
printf("Connection Failed!\n");
return; // <<<
}
Otherwise your program will likely crash, without even you could see the error notification printed.
To check what actually was going wrong with the mysql_real_connect() function (and maybe give some more useful information than just "Connection Failed!\n"), you can use the mysql_errno() function. A list of the error codes relevant for this function can be found here.
Another possibility is you are passing invalid or empty data to the INSERT statements. Put some integrity checks for the data passed from coordString, time, id.

Answer 2

Okay so I finally got the answer after I had a second pair of eyes debugging with me.
In my function that actually writes to the database when the connection is actually successful, the mysql_close(); function was written AFTER the return statements. So it was all on me with a simple error that I over looked many times.
Thanks for all the help from the commenters and the answer I got!