CA1901: P/Invoke declarations should be portable

Article
11/04/2016

Item	Value
RuleId	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.

Cause

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.

Rule description

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.

How to fix violations

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

When to suppress warnings

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);

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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