在grpc函数声明之前，空宏“ grpcapi”的效果是什么？

发布于 2025-01-19 11:34:27 字数 618 浏览 1 评论 0原文

当我在GRPC中读取代码时，我使用grpcapi作为预选赛发现了许多API。

GRPCAPI grpc_channel* grpc_cronet_secure_channel_create(
    void* engine, const char* target, const grpc_channel_args* args,
    void* reserved);

当我单击grpcapi的链接时，它是一个空的宏。

#ifndef GPRAPI
#define GPRAPI
#endif

#ifndef GRPCAPI
#define GRPCAPI GPRAPI
#endif

我了解空宏的一些用法：

防止将相同标头的多个副本包含在被
用作调试或删除敏感代码的开关，

但此处grpcapi都不属于。告诉我们功能是API，这只是一个标记吗？或对文档或其他功能的效果更大？

原文

When I read the code in gRPC, I found many APIs using GRPCAPI as qualifier.

GRPCAPI grpc_channel* grpc_cronet_secure_channel_create(
    void* engine, const char* target, const grpc_channel_args* args,
    void* reserved);

When I click the link to GRPCAPI, it's an empty macro.

#ifndef GPRAPI
#define GPRAPI
#endif

#ifndef GRPCAPI
#define GRPCAPI GPRAPI
#endif

I understand some usages of empty macro:

preventing multiple copies of the same header being included
used as a switch for debug or removing sensitive code

But here the GRPCAPI belongs to neither. Is it just a marker to tell us the function is an API? Or more effect for document or others functions?

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纵情客 2025-01-26 11:34:27

它要么用于特定于平台的属性，要么用于未来的属性。

对于 Windows DLL，您通常指定
__declspec(dllexport) 当编译库时
__declspec(dllimport) 当使用库时。

宏是编译和使用它的便捷方法，因为您只需在标头中将宏的值定义为 __declspec(dllexport)/__declspec(dllimport) 即可。
其他编译器属性也是如此，例如 GCC 上的 __attribute__(visibility(default))/__attribute__(visibility(hidden))

现在，当库静态链接时，您可以不需要所有这些，并且您将宏定义为没有值。
一个例子是：

#ifdef STATIC_LIBRARY
     #define LIBRARY_API 
#else
#ifdef LIBRARY_EXPORTS
#    define LIBRARY_API __declspec(dllexport)
#else
#    define LIBRARY_API __declspec(dllimport)
#endif


LIBRARY_API void foo(); // when statically linked, it's a simple void function. If dynamically linked, it's either dllexport when compiling the library or dllimport when consuming it.

另一种解释可以是调用约定修饰符。
x86（我只知道x86）有不同的调用约定 - 这些约定决定调用者/被调用者如何在程序集级别上处理函数的参数。

像这样的事情：

#if WIN32
#define APICALL cdecl
#else
#define APICALL 
#endif

APICALL void foo() // uses cdecl on WIN32

Its either for platform specific attributes or for future attributes.

For Windows DLLs, you usually specify
__declspec(dllexport) when compiling the library and
__declspec(dllimport) when consuming the library.

A macro is the convenient way to both compile and consume it because you only define the value of the macro to be __declspec(dllexport)/__declspec(dllimport) within the header.
the same goes for other compiler attributes, such as __attribute__(visibility(default))/__attribute__(visibility(hidden)) on GCC

Now when the library is statically linked, you don't need all that and you define the macro to have no value.
An example would be:

#ifdef STATIC_LIBRARY
     #define LIBRARY_API 
#else
#ifdef LIBRARY_EXPORTS
#    define LIBRARY_API __declspec(dllexport)
#else
#    define LIBRARY_API __declspec(dllimport)
#endif


LIBRARY_API void foo(); // when statically linked, it's a simple void function. If dynamically linked, it's either dllexport when compiling the library or dllimport when consuming it.

Another explanation can be a calling convention modifier.
x86 (I only know x86) has different calling conventions - these decide how the caller/callee treats parameters of functions on the assembly level.

Something like this:

#if WIN32
#define APICALL cdecl
#else
#define APICALL 
#endif

APICALL void foo() // uses cdecl on WIN32

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风铃鹿 2025-01-26 11:34:27

我非常感谢@RailDex的答案以及 @paulsm4的评论，这是非常鼓舞人心的。

但是grpcapi和gprapi的确切功能用于将API标记为标签。

GRPC中有一个名为使用标签Gprapi和Grpcapi，这是使用这两个标签的唯一位置。

_RE_API = r'(?:GPRAPI|GRPCAPI|CENSUSAPI)([^;]*);'

for m in re.finditer(_RE_API, text):   # match file content
...

运行脚本后，我们将获得：

...
- arguments: void* engine, const char* target, const grpc_channel_args* args, void*
    reserved
  header: include/grpc/grpc_cronet.h
  name: grpc_cronet_secure_channel_create
  return_type: grpc_channel*
...

I really appreciate the answer from @Raildex and comment from @paulsm4, which are very inspiring.

But the exactly function of GRPCAPI and GPRAPI is used to mark APIs as a label.

There is a script in grpc named list_api.py using the label GPRAPI and GRPCAPI, which is the only place using these two labels.

_RE_API = r'(?:GPRAPI|GRPCAPI|CENSUSAPI)([^;]*);'

for m in re.finditer(_RE_API, text):   # match file content
...

After running the script, we'll get:

...
- arguments: void* engine, const char* target, const grpc_channel_args* args, void*
    reserved
  header: include/grpc/grpc_cronet.h
  name: grpc_cronet_secure_channel_create
  return_type: grpc_channel*
...

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