C # Call C Functions

C code:
# Include <stdio. h>
# Include <assert. h>
# Define MAXLEN 1000
Int getline (char [], int );

// For C # Call _ declspec
_ Declspec (dllexport) void reverseline (char dest [], const char source []);

Int main (int argc, char * argv [])
{
Char currentline [MAXLEN];
Int maxcount = 0;
Int currentlen = 0;
Char resultline [MAXLEN];
While (currentlen = getline (currentline, MAXLEN ))
{
Reverseline (resultline, currentline );
Printf ("\ n % s \ n", resultline );
}

Return 0;
}
Int getline (char line [], int len)
{
// Printf ("------- start getline ----------------------- \ n ");
Char c;
Int I = 0;
For (; (I <len & (c = getchar ())! = EOF & (c! = '\ N'); I ++)
{

Line [I] = c;
// Printf ("line [% d] = % c", I, c );
}

Line [I] = '\ 0 ';
// Printf ("\ n line [% d] = null \ n", I + 1 );

// Printf ("------- end getline ----------------------- \ n ");
Return I;
}

Void reverseline (char dest [], const char source [])
{

Int I = 0;
Int len = 0;
For (I = 0; I <MAXLEN; I ++)
{
If (source [I] = '\ 0 ')
{
Len = I;
Break;
}
// Dest [I] = source [I];
}

// Printf ("\ nlen = % d \ n", len );

For (I = 0; I <len; I ++)
{
Dest [len-1-i] = source [I];
// Printf ("dest [% d] = % c", len-1-i, dest [len-1-i]);
}

Dest [len] = '\ 0 ';

}

Use MS cl.exe to generate dll

Cl.exe reverseline. c/LD
Note that/LD is in uppercase. If it is written as/ld, it is directly ignored by cl.

Compilation output written normally:
Reverseline. c
Microsoft (R) Incremental Linker Version 9.00.30729.01
Copyright (C) Microsoft Corporation. All rights reserved.

/Out: reverseline. dll
/Dll
/Implib: reverseline. lib
Reverseline. obj
Creating library reverseline. lib and object reverseline. exp

The export function does not add _ declspec (dllexport) to compile the output:
Reverseline. c
Microsoft (R) Incremental Linker Version 9.00.30729.01
Copyright (C) Microsoft Corporation. All rights reserved.

/Out: reverseline. dll
/Dll
/Implib: reverseline. lib
Reverseline. obj

C # code: Copy reverseline. dll to the. exe directory generated by C #.
C # code:

Using System;
Using System. Collections. Generic;
Using System. Linq;
Using System. Text;
Using System. Runtime. InteropServices;

Namespace CallCLib
{
Class CLib
{
[DllImport ("reverseline. dll")]
Public static extern void reverseline (StringBuilder dest, StringBuilder surce );
}
Class Program
{
Static void Main (string [] args)
{
// Char [] a = {'1', '2', '3 '};
// Char [] B = new char [] {};
StringBuilder a = new StringBuilder ("123 ");
StringBuilder B = new StringBuilder ();
CLib. reverseline (B, );

Console. WriteLine ("a = {0} B = {1}", a, B );

Console. Read ();
}
}
}
Result generated after running:
A: 123 B = 321

Problem:
(1) If you call
Public static extern void reverseline (char [] dest, char [] surce );

Char [] a = {'1', '2', '3 '};
Char [] B = new char [] {};

CLib. reverseline (B, );
Exception:
System. AccessViolationException not processed
Message = "try to read or write the protected memory. This usually indicates that other memory is damaged. "
Source = "CallCLib"
StackTrace:
In CallCLib. CLib. reverseline (Char [] dest, Char [] surce)
In the CallCLib. Program. Main (String [] args) Position E: \ lhb \ Program \ CallCLib \ Program. cs: row 23
In System. AppDomain. _ nExecuteAssembly (Assembly assembly, String [] args)
In System. AppDomain. ExecuteAssembly (String assemblyFile, Evidence assemblySecurity, String [] args)
In Microsoft. VisualStudio. HostingProcess. HostProc. RunUsersAssembly ()
In System. Threading. ThreadHelper. ThreadStart_Context (Object state)
In System. Threading. ExecutionContext. Run (ExecutionContext executionContext, ContextCallback callback, Object state)
In System. Threading. ThreadHelper. ThreadStart ()
InnerException:
(2) If you call
Public static extern void reverseline (char [] dest, char [] surce );

String a = "123 ";
String B = "";

CLib. reverseline (B, );

Result generated after running:
A = 123 B =

(2) If the export function in c does not add _ declspec (dllexport), it is directly void reverseline (char dest [], const char source []);
Exception:
System. EntryPointNotFoundException not processed
Message = "unable to find the entry point named" reverseline "in DLL" reverseline. dll. "
Source = "CallCLib"
TypeName = ""
StackTrace:
In CallCLib. CLib. reverseline (Char [] dest, Char [] surce)
In the CallCLib. Program. Main (String [] args) Position E: \ lhb \ Program \ CallCLib \ Program. cs: row 23
In System. AppDomain. _ nExecuteAssembly (Assembly assembly, String [] args)
In System. AppDomain. ExecuteAssembly (String assemblyFile, Evidence assemblySecurity, String [] args)
In Microsoft. VisualStudio. HostingProcess. HostProc. RunUsersAssembly ()
In System. Threading. ThreadHelper. ThreadStart_Context (Object state)
In System. Threading. ExecutionContext. Run (ExecutionContext executionContext, ContextCallback callback, Object state)
In System. Threading. ThreadHelper. ThreadStart ()
InnerException:

Q: Is it a function written in the c standard library that cannot be called by. net without modifying the c source code (such as adding _ declspec or defining the def file?