equivalent char* in C#
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12-09-2019 - |
Question
I have a dll that is written in c++. And I am p/invoking to call the functions.
I have this c++ declaration.
int dll_registerAccount(char* username, char* password);
I have done this dllimport declaration:
[DllImport("pjsipDlld")]
static extern int dll_registerAccount(IntPtr username, IntPtr password);
Would my DllImport be the equivalent to the c++ using IntPtr?
Many thanks for any advice,
Solution
The C# way of doing this is by letting the marshaler handle the char*
stuff while you work with a string:
[DllImport("pjsipDlld")]
static extern int dll_registerAccount(
[MarshalAs(UnmanagedType.LPStr)]string username,
[MarshalAs(UnmanagedType.LPStr)]string password);
Replace LPStr
with LPWStr
if you're working with wide chars.
OTHER TIPS
StringBuilder for char*, since the length is unknown?
[DllImport("pjsipDlld")]
static extern int dll_registerAccount(StringBuilder username, StringBuilder password);
[DllImport("pjsipDlld", CharSet = CharSet.Ansi)]
static extern int dll_registerAccount(string username, string password);
Be aware of calling conventions, this tripped me up. In my case I need to call a C++ DLL but with C-style exports, which uses the cdecl
calling convention. If you have the luxury of having the source Visual Studio Solution, go to Properties -> C/C++ -> Advanced and find it under "Calling Convention". This fix it for me:
[DllImport(DllName, CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
// bool MyFunction(char* fileName) <-- From the DLL
static extern bool MyFunction(string fileName);
[DllImport("DLL loction"),EntryPoint = "dll_registerAccount", CallingConvention = CallingConvention.Cdecl)]
[return : MarshalAs(UnmanagedType.I4)]
static extern int dll_registerAccount(
[MarshalAs(UnmanagedType.LPStr)]string username,
[MarshalAs(UnmanagedType.LPStr)]string password);
- 'cdecl' is the default calling convention for C and C++ programs
- Refer these doc1 for more knowladge