CA1901: P/Invoke declarations should be portable

CA1901: P/Invoke declarations should be portable

 

TypeName

PInvokeDeclarationsShouldBePortable

CheckId

CA1901

Category

Microsoft.Portability

Breaking Change

Breaking - If the P/Invoke is visible outside the assembly. Non Breaking - If the P/Invoke is not visible outside the assembly.

This rule evaluates the size of each parameter and the return value of a P/Invoke and verifies that their size, when marshaled to unmanaged code on 32-bit and 64-bit platforms, is correct. The most common violation of this rule is to pass a fixed-sized integer where a platform-dependent, pointer-sized variable is required.

Either of the following scenarios violates this rule occurs:

  • The return value or parameter is typed as a fixed-size integer when it should be typed as an IntPtr.

  • The return value or parameter is typed as an IntPtr when it should be typed as a fixed-size integer.

You can fix this violation by using IntPtr or UIntPtr to represent handles instead of Int32 or UInt32.

You should not suppress this warning.

Example

The following example demonstrates a violation of this rule.

internal class NativeMethods
{
    [DllImport("shell32.dll", CharSet=CharSet.Auto)]
    internal static extern IntPtr ExtractIcon(IntPtr hInst, 
        string lpszExeFileName, IntPtr nIconIndex);
}

In this example, the nIconIndex parameter is declared as an IntPtr, which is 4 bytes wide on a 32-bit platform and 8 bytes wide on a 64-bit platform. In the unmanaged declaration that follows, you can see that nIconIndex is a 4-byte unsigned integer on all platforms.

HICON ExtractIcon(HINSTANCE hInst, LPCTSTR lpszExeFileName, 
    UINT nIconIndex);

Example

To fix the violation, change the declaration to the following:

internal class NativeMethods{
    [DllImport("shell32.dll", CharSet=CharSet.Auto)] 
    internal static extern IntPtr ExtractIcon(IntPtr hInst, 
        string lpszExeFileName, uint nIconIndex);
}
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