• <ins id="pjuwb"></ins>
    <blockquote id="pjuwb"><pre id="pjuwb"></pre></blockquote>
    <noscript id="pjuwb"></noscript>
          <sup id="pjuwb"><pre id="pjuwb"></pre></sup>
            <dd id="pjuwb"></dd>
            <abbr id="pjuwb"></abbr>
            隨筆 - 45  文章 - 129  trackbacks - 0
            <2007年1月>
            31123456
            78910111213
            14151617181920
            21222324252627
            28293031123
            45678910

            專注于C++ P2P STL GP OpenSource等
            Google

            常用鏈接

            留言簿(10)

            隨筆分類

            隨筆檔案

            相冊

            朋友

            • .NET

            搜索

            •  

            最新評論

            閱讀排行榜

            評論排行榜

            先講#和#@字符:這兩個比較類似:前者是將所代表的東西字符串化,后者是將代表的東西字符化。

            而##可以說是個符號粘合劑。(Modern C++中用來做編譯時期內存檢查--2.1節 就是用了這個符號)

            #的用法

            The number-sign or "stringizing" operator (#) converts macro parameters (after expansion) to string constants. It is used only with macros that take arguments. If it precedes a formal parameter in the macro definition, the actual argument passed by the macro invocation is enclosed in quotation marks and treated as a string literal. The string literal then replaces each occurrence of a combination of the stringizing operator and formal parameter within the macro definition.

            White space preceding the first token of the actual argument and following the last token of the actual argument is ignored. Any white space between the tokens in the actual argument is reduced to a single white space in the resulting string literal. Thus, if a comment occurs between two tokens in the actual argument, it is reduced to a single white space. The resulting string literal is automatically concatenated with any adjacent string literals from which it is separated only by white space.

            Further, if a character contained in the argument usually requires an escape sequence when used in a string literal (for example, the quotation mark (") or backslash (\) character), the necessary escape backslash is automatically inserted before the character. The following example shows a macro definition that includes the stringizing operator and a main function that invokes the macro:

            #define stringer( x ) printf( #x "\n" )
            
            int main()
            {
                stringer( In quotes in the printf function call\n ); 
                stringer( "In quotes when printed to the screen"\n );   
                stringer( "This: \"  prints an escaped double quote" );
            }

            Such invocations would be expanded during preprocessing, producing the following code:

            int main()
            {
               printf( "In quotes in the printf function call\n" "\n" );
               printf( "\"In quotes when printed to the screen\"\n" "\n" );
               printf( "\"This: \\\" prints an escaped double quote\"" "\n" );
            }

            When the program is run, screen output for each line is as follows:

            In quotes in the printf function call
            
            "In quotes when printed to the screen"
            
            "This: \" prints an escaped double quotation mark"

            Microsoft Specific

            The Microsoft C (versions 6.0 and earlier) extension to the ANSI C standard that previously expanded macro formal arguments appearing inside string literals and character constants is no longer supported. Code that relied on this extension should be rewritten using the stringizing (#) operator.

            END Microsoft Specific

            #@的用法


            Microsoft Specific

            The charizing operator can be used only with arguments of macros. If #@ precedes a formal parameter in the definition of the macro, the actual argument is enclosed in single quotation marks and treated as a character when the macro is expanded. For example:

            #define makechar(x)  #@x

            causes the statement

            a = makechar(b);

            to be expanded to

            a = 'b';

            The single-quotation character cannot be used with the charizing operator.

            END Microsoft Specific

            ##的用法

            The double-number-sign or "token-pasting" operator (##), which is sometimes called the "merging" operator, is used in both object-like and function-like macros. It permits separate tokens to be joined into a single token and therefore cannot be the first or last token in the macro definition.

            If a formal parameter in a macro definition is preceded or followed by the token-pasting operator, the formal parameter is immediately replaced by the unexpanded actual argument. Macro expansion is not performed on the argument prior to replacement.

            Then, each occurrence of the token-pasting operator in token-string is removed, and the tokens preceding and following it are concatenated. The resulting token must be a valid token. If it is, the token is scanned for possible replacement if it represents a macro name. The identifier represents the name by which the concatenated tokens will be known in the program before replacement. Each token represents a token defined elsewhere, either within the program or on the compiler command line. White space preceding or following the operator is optional.

            This example illustrates use of both the stringizing and token-pasting operators in specifying program output:

            #define paster( n ) printf( "token" #n " = %d", token##n )
            int token9 = 9;

            If a macro is called with a numeric argument like

            paster( 9 );

            the macro yields

            printf( "token" "9" " = %d", token9 );

            which becomes

            printf( "token9 = %d", token9 );
            posted on 2007-01-19 14:03 CPP&&設計模式小屋 閱讀(1624) 評論(1)  編輯 收藏 引用 所屬分類: 其他

            FeedBack:
            # re: 關于 ## ,#以及#@的用法 2007-04-21 18:47 heweitykc
            c++整的這么復雜啊 以后怎么維護啊!  回復  更多評論
              
            少妇久久久久久被弄高潮| 亚洲欧美精品伊人久久| 亚洲AV日韩精品久久久久| 久久精品亚洲日本波多野结衣| 狠色狠色狠狠色综合久久| 久久久久亚洲精品男人的天堂| 久久人人爽人人人人片av| 国产精品VIDEOSSEX久久发布| 囯产极品美女高潮无套久久久| 99久久精品免费看国产| 午夜天堂精品久久久久| 色婷婷久久综合中文久久一本| 精品999久久久久久中文字幕| 亚洲中文字幕无码久久2017| 久久精品中文字幕第23页| 久久91亚洲人成电影网站| 亚洲伊人久久大香线蕉综合图片| 国产成人精品综合久久久| 亚洲中文字幕无码久久综合网| 国产激情久久久久影院老熟女免费| 久久久人妻精品无码一区| 久久se精品一区精品二区国产| 99久久99久久精品国产片果冻| 污污内射久久一区二区欧美日韩 | 青青草原精品99久久精品66| 国产成人精品久久亚洲高清不卡 | 精品乱码久久久久久久| 色综合久久久久久久久五月| 国产毛片欧美毛片久久久| 久久久无码精品亚洲日韩京东传媒| 久久国产影院| 久久www免费人成精品香蕉| 国产精品欧美久久久久天天影视| 97精品国产91久久久久久| 久久成人影院精品777| 久久福利青草精品资源站| 一级做a爱片久久毛片| 国产精品久久久久久一区二区三区| 粉嫩小泬无遮挡久久久久久| 久久精品99久久香蕉国产色戒| 久久天天婷婷五月俺也去|