CodeQL documentation

Calls to unmanaged code

ID: cs/call-to-unmanaged-code
Kind: problem
Severity: recommendation
Precision: high
Tags:
   - reliability
   - maintainability
Query suites:
   - csharp-security-and-quality.qls

Click to see the query in the CodeQL repository

Microsoft defines two broad categories for source code. Managed code compiles into bytecode and is then executed by a virtual machine. Unmanaged code is compiled directly into machine code. All C# code is managed but it is possible to call external unmanaged code. This rule finds calls to extern methods that are implemented by unmanaged code. Managed code has many advantages over unmanaged code such as built in memory management performed by the virtual machine and the ability to run compiled programs on a wider variety of architectures.

Recommendation

Consider whether the calls could be replaced by calls to managed code instead.

Example

This example shows a function that displays a message box when clicked. It is implemented with unmanaged code from the User32.dll library.

using System;
using System.Windows.Forms;
using System.Runtime.InteropServices;

public partial class UnmanagedCodeExample : Form
{
    [DllImport("User32.dll")]
    public static extern int MessageBox(int h, string m, string c, int type);

    private void btnSayHello_Click(object sender, EventArgs e)
    {
        MessageBox(0, "Hello World", "Title", 0); // BAD
    }
}

Fixing by Using Managed Code

This code example does the exact same thing except it uses managed code to do so.

using System;
using System.Windows.Forms;

public partial class ManagedCodeExample : Form
{
    private void btnSayHello_Click(object sender, EventArgs e)
    {
        MessageBox.Show("Hello World", "Title");
    }
}

References