marshalling a struct containing string

Question

i basically want to take int name and string age from user in c# and send it to dll method written in c which take int and char[50] arguments in it and return string .i crea

Answer 1

Within a struct, to marshal char arrays defined as char[] you should use the UnmanagedType.ByValTStr instead.

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct Argument
{
    public int age;

    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 50)]
    public string name;
}

Answer 2

You need to change your struct definition of Argument to either

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct Argument
{
    public int age;

    [MarshalAs(UnmanagedType.LPStr, SizeConst = 50)]
    public string name;
}

- or -

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
unsafe public struct Argument
{
    public int age;
    fixed char name[50];
}

You might also find the article Default Marshaling for Strings helpful.