pragma comment的使用

以下内容转载自http://www.cppblog.com/xczhang/archive/2008/01/10/40866.html

该宏放置一个注释到对象文件或者可执行文件。

#pragma comment( comment-type [,"commentstring"] )comment-type是一个预定义的标识符，指定注释的类型，应该是compiler，exestr，lib，linker之一。commentstring是一个提供为comment-type提供附加信息的字符串，Remarks：1、compiler：放置编译器的版本或者名字到一个对象文件，该选项是被linker忽略的。2、exestr：在以后的版本将被取消。3、lib：放置一个库搜索记录到对象文件中，这个类型应该是和commentstring（指定你要Liner搜索的lib的名称和路径）这个库的名字放在Object文件的默认库搜索记录的后面，linker搜索这个这个库就像你在命令行输入这个命令一样。你可以在一个源文件中设置多个库记录，它们在object文件中的顺序和在源文件中的顺序一样。如果默认库和附加库的次序是需要区别的，使用Z编译开关是防止默认库放到object模块。4、linker：指定一个连接选项，这样就不用在命令行输入或者在开发环境中设置了。只有下面的linker选项能被传给Linker.

• /DEFAULTLIB

• /EXPORT

• /INCLUDE

• /MANIFESTDEPENDENCY

• /MERGE

• /SECTION

(1)/DEFAULTLIB:library/DEFAULTLIB 选项将一个 library 添加到 LINK 在解析引用时搜索的库列表。用 /DEFAULTLIB指定的库在命令行上指定的库之后和 .obj 文件中指定的默认库之前被搜索。

忽略所有默认库 (/NODEFAULTLIB) 选项重写 /DEFAULTLIB:library。如果在两者中指定了相同的 library 名称，忽略库 (/NODEFAULTLIB:library) 选项将重写 /DEFAULTLIB:library。

(2)/EXPORT:entryname[,@ordinal[,NONAME]][,DATA]

使用该选项，可以从程序导出函数，以便其他程序可以调用该函数。也可以导出数据。通常在 DLL 中定义导出。entryname 是调用程序要使用的函数或数据项的名称。ordinal 在导出表中指定范围在 1 至 65,535 的索引；如果没有指定 ordinal，则 LINK 将分配一个。NONAME 关键字只将函数导出为序号，没有 entryname。

DATA 关键字指定导出项为数据项。客户程序中的数据项必须用 extern __declspec(dllimport) 来声明。
有三种导出定义的方法，按照建议的使用顺序依次为：

1. 源代码中的 __declspec(dllexport)

2. .def 文件中的 EXPORTS 语句

3. LINK 命令中的 /EXPORT 规范

所有这三种方法可以用在同一个程序中。LINK 在生成包含导出的程序时还创建导入库，除非生成中使用了 .exp 文件。
LINK 使用标识符的修饰形式。编译器在创建 .obj 文件时修饰标识符。如果 entryname 以其未修饰的形式指定给链接器（与其在源代码中一样），则 LINK 将试图匹配该名称。如果无法找到唯一的匹配名称，则 LINK 发出错误信息。当需要将标识符指定给链接器时，请使用 Dumpbin 工具获取该标识符的修饰名形式。

(3)/INCLUDE:symbol

/INCLUDE 选项通知链接器将指定的符号添加到符号表。

若要指定多个符号，请在符号名称之间键入逗号 (,)、分号 (;) 或空格。在命令行上，对每个符号指定一次 /INCLUDE:symbol。
链接器通过将包含符号定义的对象添加到程序来解析 symbol。该功能对于添包含不会链接到程序的库对象非常有用。用该选项指定符号将通过 /OPT:REF 重写该符号的移除。

我们经常用到的是#pragma   comment（lib，"*.lib"）这类的。#pragma   comment(lib,"Ws2_32.lib")表示链接Ws2_32.lib这个库。   和在工程设置里写上链入Ws2_32.lib的效果一样，不过这种方法写的   程序别人在使用你的代码的时候就不用再设置工程settings了

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以下内容转载自http://msdn.microsoft.com/en-us/library/7f0aews7(v=VS.80).aspx

Places a comment record into an object file or executable file.
#pragma comment( comment-type [,"commentstring"] )
Remarks
The comment-type is one of the predefined identifiers, described below, that specifies the type of comment record. The optional commentstring is a string literal that provides additional information for some comment types. Because commentstring is a string literal, it obeys all the rules for string literals with respect to escape characters, embedded quotation marks ("), and concatenation.
compiler
Places the name and version number of the compiler in the object file. This comment record is ignored by the linker. If you supply a commentstring parameter for this record type, the compiler generates a warning.
exestr
Places commentstring in the object file. At link time this string is placed in the executable file. The string is not loaded into memory when the executable file is loaded; however, it can be found with a program that finds printable strings in files. One use for this comment-record type is to embed a version number or similar information in an executable file.
exestr is deprecated and will be removed in a future release; the linker does not process the comment record.
lib
Places a library-search record in the object file. This comment type must be accompanied by a commentstring parameter containing the name (and possibly the path) of the library that you want the linker to search. The library name follows the default library-search records in the object file; the linker searches for this library just as if you had named it on the command line provided that the library is not specified with /nodefaultlib. You can place multiple library-search records in the same source file; each record appears in the object file in the same order in which it is encountered in the source file.
If the order of the default library and an added library is important, compiling with the /Zl switch will prevent the default library name from being placed in the object module. A second comment pragma then can be used to insert the name of the default library after the added library. The libraries listed with these pragmas will appear in the object module in the same order they are found in the source code.
linker
Places a linker option in the object file. You can use this comment-type to specify a linker option instead of passing it to the command line or specifying it in the development environment. For example, you can specify the /include option to force the inclusion of a symbol:
#pragma comment(linker, "/include:__mySymbol")
Only the following (comment-type) linker options are available to be passed to the linker identifier:
/DEFAULTLIB
/EXPORT
/INCLUDE
/MANIFESTDEPENDENCY
/MERGE
/SECTION
user
Places a general comment in the object file. The commentstring parameter contains the text of the comment. This comment record is ignored by the linker.
The following pragma causes the linker to search for the EMAPI.LIB library while linking. The linker searches first in the current working directory and then in the path specified in the LIB environment variable.
#pragma comment( lib, "emapi" )
The following pragma causes the compiler to place the name and version number of the compiler in the object file:
#pragma comment( compiler )
Note
For comments that take a commentstring parameter, you can use a macro in any place where you would use a string literal, provided that the macro expands to a string literal. You can also concatenate any combination of string literals and macros that expand to string literals. For example, the following statement is acceptable:
#pragma comment( user, "Compiled on " __DATE__ " at " __TIME__ )