获取错误：类mysqli的对象无法在第5行转换为字符串[重复]
This question is an exact duplicate of:
I'm getting this error:
Catchable fatal error: Object of class mysqli could not be converted to string in C:\xampp\htdocs\gym\userAvailability.php on line 5
And this is the code:
<?php
function username_exists($username, $con){
$sql = "SELECT * FROM admin WHERE username = '$username'";
$result = mysqli_query($con, sql);
$resultarr = mysqli_fetch_assoc($result);
if(!mysqli_num_rows($result) == 1){
return true;
}else{
return false;
}
}
I've also checked all the variable name from the .php file that the function username_exist is being used and it is all correct. Any ideas on how to fix this?
</div>
For one, this code is vulnerable to SQL injection - you should use prepared statements with placeholders instead. You're also fetching the result, which isn't used - so you can get rid of the mysqli_fetch_assoc() inside this function.
Your actual issue though, is a dollar-sign missing in front of your $sql and the logic here if(!mysqli_num_rows($result) == 1) { is inverse. If there is a result, you basically get !1 == 1, which is false (as !1 becomes 0, so you get 0 == 1). So the inverse-operator ! had the result be the other way around.
Cleaned a bit, fixed the logical issue and added prepared statements, would look like this
function username_exists($username, $con){
$stmt = $con->prepare("SELECT * FROM admin WHERE username = ?");
$stmt->bind_param('s', $username);
$stmt->execute();
$stmt->store_result();
$num_rows = $stmt->num_rows;
$stmt->close();
return $num_rows == 1 ? true : false;
}
This function would now return true if the username is found in the database. You should now use this function like
if (!username_exists($_POST['username'], $con) {
/* Do the insert to the database here */
} else {
/* The username was taken!
Don't perform the INSERT query */
}
When passing the $username parameter to the function, use the raw username (don't use mysqli_real_escape_string() on it here, since we're using prepared statements).
You might also want to look into adding the UNIQUE constraint for your username-column in the database.