MySQL and varargs

Question

I have the following query that is stored in buffer, and then is executed using my own conn.executeQuery().

char buffer[QUERY_MAX];
snprintf(buffer, QUERY_MAX, "SELECT * FROM players WHERE player_id = %d", 1);
conn.executeQuery(buffer);

While this works fine, I wonder if it can be simplified as something similar to...

conn.executeQuery("SELECT * FROM players WHERE player_id = "%d", 1);

My function:

bool SQLConnection::executeQuery(const char *query)
{ 
// Validate connection.
if (!m_connected)
    return false;  

// Execute the query
int status = mysql_query(&m_conn, query);

if (status != 0) {
    sprintf(m_errorMessage, "Error: %s", mysql_error(&m_conn)); 
    return false;
}

// Store the result
m_result = mysql_store_result(&m_conn);

return true;
}

I'm aware of varargs, and tried to follow the example here (Variable number of arguments in C++?), but I'm not simply trying to read the varargs, but to include them in the query, which is apparently troublesome for me.

Any thoughts are welcomed, thanks.

score 1 · Answer 1 · answered Jul 23 '17 at 00:18

You need a prepared statement instead, like the following

MYSQL_STMT *stmt;
MYSQL_BIND params[1 /* Here it will be the number of arguments */];
MYSQL_BIND result[1 /* Here it will be the number of columns in the result row */];
int value;
const char *query;
int id;

memset(params, 0, sizeof params);
memset(result, 0, sizeof result);
// Assuming `mysql' is an initialized MYSQL object
stmt = mysql_stmt_init(mysql);
if (stmt == NULL)
    return
// `SELECT ID' just to illustrate how you can select an integer
//             value
query = "SELECT ID FROM players WHERE player_id = ?";
if (mysql_stmt_prepare(stmt, query, strlen(query)) != 0)
    goto error;
value = 1;

result[0].buffer_type = MYSQL_TYPE_LONG;
result[0].buffer = &id;

params[0].buffer_type = MYSQL_TYPE_LONG;
params[0].buffer = &value;
if (mysql_stmt_bind_param(stmt, params) != 0)
    goto error;
if (mysql_stmt_bind_result(stmt, result) != 0)
    goto error;
if (mysql_stmt_execute(stmt) != 0)
    goto error;
if (mysql_stmt_fetch(stmt) != 0)
    goto error;
// Now all the columns are in the buffers of `result'
// or the bound variables (which is why we pass their address)
fprintf(stdout, "%d\n", id);

error:

mysql_stmt_close(stmt);

MySQL and varargs

1 Answers1