c# 调用 c dll 例子

 1 // case 1 传递 int* /////////////////////////////////////////////
 2 extern “C” __declspec(dllexport) int mySum(int *a2,int *b2)
 3 {
 4 // 改变 a1, b1
 5 *a2=...
 6 *b2=...
 7  return a+b;
 8 }
 9 public static extern int mySum (ref int a1,ref int b1); // c# 声明
10 /////////////////////////////////////////////////////////////////////
11
12 // case 2 DLL 传入 char* 打印 /////////////////////////////////////////////
13 extern “C” __declspec(dllexport)  void print(const char *str)
14 {
15     printf(str);
16 }
17 public static extern void print(string  str); // c# 声明
18 /////////////////////////////////////////////////////////////////////
19
20 // case 3 传入 char* 写回 ///////////////////////////////////////////
21 void foo(char* bar) {
22   // do write some information into char* bar
23 }
24
25 [DllImport("foobar.dll")]
26 private static external void foo(StringBuilder bar);
27
28 public String ReadFoo() {
29   StringBuilder result = new StringBuilder(256);
30   foo(result);
31   return result.ToString();
32 }
33 // 一些字符的处理
34 public String ReadFoo2() {
35     StringBuilder strBuilder = new StringBuilder(256);
36     foo(strBuilder);
37     Byte[] buf = Encoding.Unicode.GetBytes(strBuilder.ToString());
38     String result = Encoding.ASCII.GetString(buf);
39 }
40 /////////////////////////////////////////////////////////////////////
41
42 // case 4  输入数组 ////////////////////////////////////////////////
43 [DllImport("foobar.dll")]
44 private unsafe static extern void getpicture(byte* imageBuffer);
45
46 private byte[] GetImage() {
47   // size of the picture is 1024 * 1024 at RGB color, 8 bit each color
48   Byte[] rc = new Byte[1024 * 1024 * 3];
49
50   // this block contains unsafe code!!!
51   unsafe {
52     // create the pointer by disabling garbage collection and
53     // memory reallocation
54     fixed (byte* rcPrt = rc) {
55       this.getpicture(rcPtr);
56     }
57     // devalidate pointer and reenable memory reallocation and
58     // garbage collection
59   }
60   // and get safe again
61
62   return rc;
63 }
64 /////////////////////////////////////////////////////////////////

参考：https://www.gadgetweb.de/programming/38-cs-and-the-char-mess.html