CA1400: P/Invoke entry points should exist

Cause

A public or protected method is marked with the System.Runtime.InteropServices.DllImportAttribute. Either the unmanaged library could not be located or the method could not be matched to a function in the library. If the rule cannot find the method name exactly as it is specified, it looks for ANSI or wide-character versions of the method by suffixing the method name with 'A' or 'W'. If no match is found, the rule attempts to locate a function by using the *_stdcall name format (*MyMethod@12, where 12 represents the length of the arguments). If no match is found, and the method name starts with '#', the rule searches for the function as an ordinal reference instead of a name reference.

Rule description

No compile-time check is available to make sure that methods that are marked with DllImportAttribute are located in the referenced unmanaged DLL. If no function that has the specified name is in the library, or the arguments to the method do not match the function arguments, the common language runtime throws an exception.

How to fix violations

To fix a violation of this rule, correct the method that has the DllImportAttribute attribute. Make sure that the unmanaged library exists and is in the same directory as the assembly that contains the method. If the library is present and correctly referenced, verify that the method name, return type, and argument signature match the library function.

When to suppress warnings

Do not suppress a warning from this rule when the unmanaged library is in the same directory as the managed assembly that references it. It might be safe to suppress a warning from this rule in the case where the unmanaged library could not be located.

Example

The following example shows a type that violates the rule. No function that is named DoSomethingUnmanaged occurs in kernel32.dll.

using System.Runtime.InteropServices;

namespace InteroperabilityLibrary
{
   public class NativeMethods
   {
      // If DoSomethingUnmanaged does not exist, or has 
      // a different signature or return type, the following 
      // code violates rule PInvokeEntryPointsShouldExist.
      [DllImport("kernel32.dll")]
      public static extern void DoSomethingUnmanaged();
   }
}

See also

System.Runtime.InteropServices.DllImportAttribute