問題描述

我看到的Qt源代碼是這樣的:

I saw the Qt source code like this:

class Q_CORE_EXPORT QBasicAtomicInt
{
public:
...
};

Q_CORE_EXPORT 宏定義如下:

define Q_DECL_IMPORT __declspec(dllimport)

那么 __declspec(dllimport) 到底是什么意思?

So what does __declspec(dllimport) really mean?

推薦答案

__declspec 是 Microsoft 特定的屬性，允許您指定存儲(chǔ)類信息.
_{(Nitpicker's Corner:但是，許多其他編譯器供應(yīng)商(例如 GCC)現(xiàn)在支持此語言擴(kuò)展，以便與針對(duì) Microsoft 編譯器編寫的已安裝代碼庫兼容.有些甚至提供額外的存儲(chǔ)類屬??性.)}

可以指定的兩個(gè)存儲(chǔ)類屬性是 dllimport 和 dllexport.這些向編譯器表明函數(shù)或?qū)ο笫菑?DLL 導(dǎo)入或?qū)С?分別).

Two of those storage-class attributes that can be specified are dllimport and dllexport. These indicate to the compiler that a function or object is imported or exported (respectively) from a DLL.

更具體地說，它們定義了 DLL 到客戶端的接口，而無需模塊定義 (.DEF) 文件.大多數(shù)人發(fā)現(xiàn)使用這些語言擴(kuò)展比創(chuàng)建 DEF 文件要容易得多.

More specifically, they define the DLL's interface to the client without requiring a module-definition (.DEF) file. Most people find it much easier to use these language extensions than to create DEF files.

出于顯而易見的原因，__declspec(dllimport) 和 __declspec(dllexport) 通常是相互配對(duì)的.您使用 dllexport 將符號(hào)標(biāo)記為從 DLL 導(dǎo)出，然后使用 dllimport 將該導(dǎo)出的符號(hào)導(dǎo)入另一個(gè)文件.

For obvious reasons, __declspec(dllimport) and __declspec(dllexport) are generally paired with one another. You use dllexport to mark a symbol as exported from a DLL, and you use dllimport to import that exported symbol in another file.

因此，并且因?yàn)樵诰幾g DLL 時(shí)和在使用 DLL 接口的客戶端代碼中通常使用相同的頭文件，定義一個(gè)在編譯時(shí)自動(dòng)解析為適當(dāng)屬性說明符的宏是一種常見模式-時(shí)間.例如:

Because of this, and because the same header file is generally used both when compiling the DLL and in client code that consumes the DLL's interface, it is a common pattern to define a macro that automatically resolves to the appropriate attribute specifier at compile-time. For example:

#if COMPILING_DLL
    #define DLLEXPORT __declspec(dllexport)
#else
    #define DLLEXPORT __declspec(dllimport)
#endif

然后用DLLEXPORT標(biāo)記所有應(yīng)該導(dǎo)出的符號(hào).

And then marking all of the symbols that should be exported with DLLEXPORT.

據(jù)推測(cè)，這就是 Q_CORE_EXPORT 宏所做的，解析為 Q_DECL_IMPORT 或 Q_DECL_EXPORT.

Presumably, that is what the Q_CORE_EXPORT macro does, resolving to either Q_DECL_IMPORT or Q_DECL_EXPORT.

這篇關(guān)于__declspec(dllimport) 的真正含義是什么?的文章就介紹到這了，希望我們推薦的答案對(duì)大家有所幫助，也希望大家多多支持html5模板網(wǎng)！