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by: uFramer D语言论坛 http://www.d-programming-language-china.org
from: http://www.digitalmars.com/d/htomodule.html
version: 基于DMD 1.014
尽管 D 不能直接编译 C 的源代码，但它可以同 C 代码很好的衔接，可以同 C 目标文件连接，还可以调用 DLL 中的 C 函数。C 代码的接口通常位于 C 的 .h 文件中。所以，同 C 代码衔接的关键就在于将 C .h 文件转换为 D 模块。事实证明，这个工作很难采用机械的方法完成，必须有人加以判断。下面就是执行这种转换的一些指导。
Preprocessor预处理器
.h files can sometimes be a bewildering morass of layers of macros, #include files, #ifdef's, etc. D doesn't include a text preprocessor like the C preprocessor, so the first step is to remove the need for it by taking the preprocessed output. For DMC (the Digital Mars C/C++ compiler), the command:
will create a file program.lst which is the source file after all text preprocessing.
Remove all the #if, #ifdef, #include, etc. statements.
Linkage链接
通常，象下面这样将整个模块包起来：
extern (C)
{
/*...文件内容...*/
}
会使代码采用 C 的链接风格。
Types型别
可以用简单的全局替换重命名C型别到D的型别。
下面是一个32位C代码的型别对应表。( 本文出处: http://www.d-programming-language-china.org )
Mapping C type to D type | C type | D type |
| long double | real |
| unsigned long long | ulong |
| long long | long |
| unsigned long | uint |
| long | int |
| unsigned | uint |
| unsigned short | ushort |
| signed char | byte |
| unsigned char | ubyte |
| wchar_t | wchar or dchar |
| bool | bool, byte, int |
| size_t | size_t |
| ptrdiff_t | ptrdiff_t |
NULL
应该使用 NULL 宏或者 ((void*)0) 来代替 null 。
Numeric Literals数值文字量
删除所有'L'或'l'数值文字量后缀，通常C的long对应于D的int.'LL'后缀应该用'L'来代替。所有'u'后缀不用改。
String Literals字符串文字量
在多数情况下可以直接移除'L'前缀，需要时D会隐式转换到宽字符。当然也可以这样替换:
替换成:
"string"w // for 16 bit wide characters
"string"d // for 32 bit wide characters
Macros宏
象这样的宏：( 本文出处: http://www.d-programming-language-china.org )
#define FOO 1
#define BAR 2
#define ABC 3
#define DEF 40
可以被替换成:
enum
{ FOO = 1,
BAR = 2,
ABC = 3,
DEF = 40
}
或者：
const int FOO = 1;
const int BAR = 2;
const int ABC = 3;
const int DEF = 40;
象这样函数风格的宏：
#define MAX(a,b) ((a) < (b) ? (b) : (a))
可以被替换成：
int MAX(int a, int b) { return (a < b) ? b : a; }
The functions, however, won't work if they appear inside static initializers that must be evaluated at compile time rather than runtime. To do it at compile time, a template can be used:( 本文出处: http://www.d-programming-language-china.org )
#define GT_DEPTH_SHIFT (0)
#define GT_SIZE_SHIFT (8)
#define GT_SCHEME_SHIFT (24)
#define GT_DEPTH_MASK (0xffU << GT_DEPTH_SHIFT)
#define GT_TEXT ((0x01) << GT_SCHEME_SHIFT)
/* Macro that constructs a graphtype */
#define GT_CONSTRUCT(depth,scheme,size) \
((depth) | (scheme) | ((size) << GT_SIZE_SHIFT))
/* Common graphtypes */
#define GT_TEXT16 GT_CONSTRUCT(4, GT_TEXT, 16)
对应的D版本是这样的：
const uint GT_DEPTH_SHIFT = 0;
const uint GT_SIZE_SHIFT = 8;
const uint GT_SCHEME_SHIFT = 24;
const uint GT_DEPTH_MASK = 0xffU << GT_DEPTH_SHIFT;
const uint GT_TEXT = 0x01 << GT_SCHEME_SHIFT;
// Template that constructs a graphtype
template GT_CONSTRUCT(uint depth, uint scheme, uint size)
{
// notice the name of the const is the same as that of the template
const uint GT_CONSTRUCT = (depth | scheme | (size << GT_SIZE_SHIFT));
}
// Common graphtypes
const uint GT_TEXT16 = GT_CONSTRUCT!(4, GT_TEXT, 16);
Declaration Lists声明列表
D只允许同类型的声明列表，因此:( 本文出处: http://www.d-programming-language-china.org )
应该写成这样:
int* p, s;
int q;
int[3] t;
Void Parameter Lists空参数列表
空参数的函数：
在D里这样写：( 本文出处: http://www.d-programming-language-china.org )
Const Type Modifiers
Const 类型修饰符
D has const as a storage class, not a type modifier. Hence, just drop any const used as a type modifier:
void foo(const int *p, char *const q);
void foo(int* p, char* q);
Extern Global C Variables外部全局C变量
D里声明一个变量，也就是定义了一个变量。如果也在链接进来的C object文件里定义了，就是一个多次定义错误。要解决这个问题，可以使用外部存储类。例如有一个C头文件foo.h:
struct Foo { };
struct Foo bar;
可以用D模块foo.d来代替：
struct Foo { }
extern (C)
{
extern Foo bar;
}
Typedef
在 D 中 alias 等价于 C 中的 typedef ：( 本文出处: http://www.d-programming-language-china.org )
变为：
Structs结构
C的结构：
typedef struct Foo
{ int a;
int b;
} Foo, *pFoo, *lpFoo;
替换成：
struct Foo
{ int a;
int b;
}
alias Foo* pFoo, lpFoo;
Struct Member Alignment结构成员对齐
A good D implementation by default will align struct members the same way as the C compiler it was designed to work with. But if the .h file has some #pragma's to control alignment, they can be duplicated with the D align attribute:
#pragma pack(1)
struct Foo
{
int a;
int b;
};
#pragma pack()
becomes:
struct Foo
{
align (1):
int a;
int b;
}
Nested Structs嵌套结构
struct Foo
{
int a;
struct Bar
{
int c;
} bar;
};
struct Abc
{
int a;
struct
{
int c;
} bar;
};
改成D是这样的：
struct Foo
{
int a;
struct Bar
{
int c;
}
Bar bar;
}
struct Abc
{
int a;
struct
{
int c;
}
}
__cdecl, __pascal, __stdcall
int __cdecl x;
int __cdecl foo(int a);
int __pascal bar(int b);
int __stdcall abc(int c);
转换成：
extern (C) int x;
extern (C) int foo(int a);
extern (Pascal) int bar(int b);
extern (Windows) int abc(int c);
__declspec(dllimport)
__declspec(dllimport) int __stdcall foo(int a);
转换成：
export extern (Windows) int foo(int a);
__fastcall
Unfortunately, D doesn't support the __fastcall convention. Therefore, a shim will be needed, either written in C:
int __fastcall foo(int a);
int myfoo(int a)
{
return foo(int a);
}
and compiled with a C compiler that supports __fastcall and linked in, or compile the above, disassemble it with obj2asm and insert it in a D myfoo shim with inline assembler.
http://www.digitalmars.com/ctg/obj2asm.html
http://digitalmars.com/d/iasm.html( 本文出处: http://www.d-programming-language-china.org )
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