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Microsoft Visual Studio SQL server connection - invalid pointer

So, I want to create a SQL database in Microsoft SQL Management Studio and connect it to Microsoft Visual Studio. I linked the database to Visual Studio and it worked. Now, I want to open that connection to test it with a button on a windows form application. Every time I try, it says "invalid pointer" but the database name is correct. I don't know what is wrong.
I still get the invalid pointer error...My instance name is DESKTOP-BJSAO6B but it doesnt seem to work...

You need provide a proper connection string like
string connectionString =
"data source=.\SQLEXPRESS;initial catalog=student;integrated security=True;";
using (SqlConnection connection =
new SqlConnection(connectionString))
{
connection.Open();
MessageBox.Show("You are connected");
}
where SQLEXPRESS - name your MSSQL instance ( may be different). More you can see here

For Ex:
string connectionString = "Data Source=Server-Name; Initial Catalog= Database-Name;Integrated Security=True"; //If you are using a local Database.
SqlConnection conn = new SqlConnection(connectionString);
conn.Open();
MessageBox.Show("You are connected");

Can't connect to SQL Server DB

I'm trying to connect to a DB and I followed the connection string suggestions. However, I'm not a DB-guy so some things are, hrmp... less than obvious.
For instance, the DB server is within the network and the connection to it goes from another server, also in the same network. I've used the server name and port to connect to it using Management Studio so it's up and running.
This is my connection string.
System.Data.SqlClient.SqlConnection conn = new System.Data.SqlClient.SqlConnection();
conn.ConnectionString =
"integrated security=SSPI;"+
"server=server.name.as.in.management.studio,4340" +
"persist security info=False;database=NameOfTheDb";
The authentication is done using AD and the error message is 40 - can't find the server. Besides the obvious - the server can't be found - what can I do to trouble-shoot this, obtain more information etc.?
I'm at a customer and their system is not as well documented as one'd like. I get very little information and the coverage is questionable. The person who set up the attrocity is gone since a long time.
Suggestions are welcome.
EDIT
Following the corrections provided, I'm getting error code 0 - The requested name is valid but no data of the requested type was found.
What do I do with this?! :)

System.Data.SqlClient.SqlConnection conn = new System.Data.SqlClient.SqlConnection();
conn.ConnectionString =
"integrated security=SSPI;"+
"Data Source=myServerAddress;" +
"persist security info=False;" +
"Initial Catalog=NameOfTheDb";
Hope this helps.

Sure servce in Managmnet Sql Server is Start.
You can do that by go to ---> Control Panel-->All Control Panel Items-->Administrative Tools--Services --> SQL Server(MSSQLSERVER) and click Start.
System.Data.SqlClient.SqlConnection conn = new System.Data.SqlClient.SqlDbConnection();
conn.ConnectionString =
"Data Source=ServerName;" +
"Initial Catalog=DataBaseName;" +
"User id=UserName;" +
"Password=Secret;";
conn.Open();

How to backup from .mdf database that I created

I created a .mdf database file with Visual Studio 2008. I can retrieve and insert data into database but when I want to backup I receive an error.
My code:
string con = #"Data Source=.\SQLEXPRESS;AttachDbFilename=|C:\test\Data|\DB.mdf;Integrated Security=True;User Instance=True";
connect = new SqlConnection(con);
connect.Open();
SqlCommand command = new SqlCommand(#"backup database [" + System.Windows.Forms.Application.StartupPath + "\\Data\\DB.mdf] to disk ='"+str+"' with init,stats=10",connect);
command.ExecuteNonQuery();
connect.Close();
MessageBox.Show("The support of the database was successfully performed", "Back", MessageBoxButtons.OK, MessageBoxIcon.Information);
The error is:
error : invalid value for key 'attachdbfilename'.

Seems like your connection string is incorrect.
Try this one:
string con = #"Data Source=.\SQLEXPRESS;AttachDbFilename=C:\test\Data\DB.mdf;Integrated Security=True;User Instance=True";
For more options, have a look at: http://www.connectionstrings.com/sql-server-2005

This is for SQL Server 2012 and .NET 4.0.1 only.
If you have those, you should be able to use AttachDbFilename.
Anyway, if you have an .MDF for embedded database and the instance is not running, you can just copy .MDF and .LDF to back up.

just use your connection string as
SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["<your connection string name from your app.config file>"].ConnectionString);
i tried it and it worked for me.

Connecting to local SQL Server database using C#

Suppose I have created a SQL Server database called Database1.mdf in the App_Data folder in Visual Studio with a table called Names.
How could I establish a connection to read the table values using C#?
So far I've tried something like this:
SqlConnection conn = new SqlConnection("Server=localhost;Database=Database1;");
conn.Open();
// create a SqlCommand object for this connection
SqlCommand command = conn.CreateCommand();
command.CommandText = "Select * from Names";
But I get an error:
database not found/error connecting to database

In Data Source (on the left of Visual Studio) right click on the database, then Configure Data Source With Wizard. A new window will appear, expand the Connection string, you can find the connection string in there

If you use SQL authentication, use this:
using System.Data.SqlClient;
SqlConnection conn = new SqlConnection();
conn.ConnectionString =
"Data Source=.\SQLExpress;" +
"User Instance=true;" +
"User Id=UserName;" +
"Password=Secret;" +
"AttachDbFilename=|DataDirectory|Database1.mdf;"
conn.Open();
If you use Windows authentication, use this:
using System.Data.SqlClient;
SqlConnection conn = new SqlConnection();
conn.ConnectionString =
"Data Source=.\SQLExpress;" +
"User Instance=true;" +
"Integrated Security=true;" +
"AttachDbFilename=|DataDirectory|Database1.mdf;"
conn.Open();

If you're using SQL Server express, change
SqlConnection conn = new SqlConnection("Server=localhost;"
+ "Database=Database1;");
to
SqlConnection conn = new SqlConnection("Server=localhost\SQLExpress;"
+ "Database=Database1;");
That, and hundreds more connection strings can be found at http://www.connectionstrings.com/

SqlConnection c = new SqlConnection(#"Data Source=localhost;
Initial Catalog=Northwind; Integrated Security=True");

You try with this string connection
Server=.\SQLExpress;AttachDbFilename=|DataDirectory|Database1.mdf;Database=dbname; Trusted_Connection=Yes;

I like to use the handy process outlined here to build connection strings using a .udl file. This allows you to test them from within the udl file to ensure that you can connect before you run any code.
Hope that helps.

Visual Studio 2019 (and probably a few previous versions).
View -> SQL Server Object Explorer
Top of the tree is 'SQL Server'
Under 'SQL Server', are couple of '(localdb)....'
Expand the (localdb)... -> Databases until you find your db.
Database Name (eg. Database1) -> Right-click -> Properties, and scroll the many properties (eg. "ANSI
NULL Default"). Find the "Connection string" property, copy the value
into your code, and you're running.

Error trying to connect to SQL Server using C#

My code is as follows:
string constring = "Data Source=132.186.127.169"+ "Initial Catalog=CadPool1;" + "Integrated Security=True";
SqlConnection con;
con = new SqlConnection(constring);
con.Open();
string query="SELECT * from CadPoolProjectTable1";
SqlCommand cmd = new SqlCommand(query, con);
cmd.ExecuteNonQuery();
MessageBox.Show("selected");
con.Close();
I am getting error at the line con.Open();. The error is:
A network-related or instance-specific
error occurred while establishing a
connection to SQL Server. The server
was not found or was not accessible.
Verify that the instance name is
correct and that SQL Server is
configured to allow remote
connections. (provider: Named Pipes
Provider, error: 40 - Could not open a
connection to SQL Server)

You are missing a ';' after the server name in the connection string.
string constring = "Data Source=132.186.127.169"+ "Initial Catalog=CadPool1;" + "Integrated Security=True";
It should be
string constring = "Data Source=132.186.127.169;"+ "Initial Catalog=CadPool1;" + "Integrated Security=True";
The error says that your app was not able to connect to the server. I would do the following.
Check for the server address (on a quick look it looks good)
Connect using management studio and in your case it should have worked.
It means the issue is with the code. Since you are concatenating the string I would debug the code and see what the end result for the connection string is.
Tip:If it is a web application add the connection string to web.config file. More info here How to: Read Connection Strings from the Web.config File

You're missing a semicolon in your connection string
Data Source=132.186.127.169;"+ "Initial...
^
If you need to build the connection string yourself you can use the SqlConnectionStringBuilder class. That way you won't to be as troubled by these subtle mistakes.

Your connection string is wrong:
string constring =
"Data Source=132.186.127.169;Initial Catalog=CadPool1;Integrated Security=True";
You don't need to concatenate the strings together, but more importantly, you were missing the semi-colon ";" between the data source and the initial catalog settings.

First, you are missing a ; (semicolon) between Data Source and Initial Catalog.
Second, if this is a newly installed SQL Server instance, you may need to go into SQL Server Configuration Manager, and enable the protocol(s) you'll need.

Please check if you can ping the server mentioned via cmd
Also try telnet to the server from your machine.
One more thing to check would be port the server is configured for if its not the default one you will have to add the port as 132.186.127.169,XXX

Servername in the connection string is wrong. and also since there are no dynamic values you don't need string concatenation. Change it to:
string constring = "Data Source=132.186.127.169;
Initial Catalog=CadPool1;
Integrated Security=True";