FD_SET编译器警告，为什么那个特别的warniing？ [英] FD_SET compiler warning, why that particular warniing?
问题描述
我的一个程序中有一个编辑错误给这一行（两个
左括号，一个右）：
FD_SET（（ncmd- > cmd_in_fd，& read_set）;
编译时使用
gcc -Wall -pedantic -stc = c99
它为该行号发出此警告：
错误：''FD_SET''未声明（首次使用此功能）
>
没有任何争论说代码行是错误的。我很好奇
虽然为什么编译器会选择发出特定的消息。
这是最令人困惑的，因为FD_SET呼叫在此之前和之后，
并且它们没有产生这些未声明的警告。
问候，
David Mathog
David Mathog写道：
我的一个程序中有一个编辑错误给出了这一行（两个
左括号，右边一个）：
FD_SET（（ncmd-> cmd_in_fd，& read_set）;
编译为
gcc -Wall -pedantic -stc = c99
它为该行号发出此警告：
错误：''FD_SET''未声明（在此函数中首次使用）
没有争论说代码行是错误的。我很好奇
虽然为什么编译器会选择发出那条特定的消息。
由于FD_SET调用之前和之后都是最令人困惑的，
并且他们没有产生这些未声明的警告。
如何定义FD_SET？
在文章< fk ********* *@naig.caltech.edu>，
David Mathog< ma **** @ caltech.eduwrote：
>那里在我的一个程序中给出了这一行的编辑错误（两个
左括号，一个右）：
FD_SET（（ncmd- > cmd_in_fd，& read_set）;
>使用
编译时
gcc -Wall -pedantic -stc = c99
>它为该行号发出此警告：
错误：''FD_SET''未声明（在此函数中首次使用）
> ;没有任何争论说代码行是wro我很好奇
虽然为什么编译器会选择发出那个特定的消息。
这是最令人困惑的，因为FD_SET调用先于和跟随这个，
并且他们没有生成这些未申报"警告。
假设FD_SET是一个类似于对象的宏，那么由于缺少
括号，该行不是类似于对象的调用宏
因此FD_SET不会被识别为该行的宏名称。
-
所以你找到了你的解决方案
你最后的贡献是什么？
- Supertramp（傻瓜的序曲）
ro ****** @ ibd.nrc-cnrc.gc.ca （Walter Roberson）写道：< br>
文章< fk ********** @ naig.caltech.edu>，
David Mathog< ma****@caltech.eduwrote：
>>我的一个程序中有一个编辑错误给出了这一行（两个
左括号，右边一个）：
> FD_SET（（ncmd-> cmd_in_fd，& read_set）;
>>使用
编译时< blockquote class =post_quotes>
> gcc -Wall -pedantic -stc = c99
>>它发出此警告对于该行号：
>错误：''FD_SET''未声明（首次在此函数中使用）
>>没有争论说代码行是错误的。我很好奇
虽然为什么编译器会选择发出特定的消息。<由于FD_SET调用之前和之后都是最令人困惑的，
并且他们没有生成这些未声明的警告。
假设FD_SET是一个类似对象的宏，然后由于缺少
括号，该行不是类似对象的调用宏的阳离子
因此FD_SET不会被识别为该行的宏名称。
这没有意义。要扩展，一个类似对象的宏
不需要跟随任何特定的令牌。如果你实际上意味着类似函数的宏，那么预处理器将继续从
源文件的后续行读取参数
;在同一条线上没有右括号
不会阻止它扩展
宏的想法。
-
在我的Egotistical Opinion中，大多数人的C程序应该向下缩进六英尺b $ b英尺向下并覆盖着污垢。 - Blair P. Houghton
There was an editing error in one of my programs giving this line (two
left parentheses, one right):
FD_SET((ncmd->cmd_in_fd,&read_set);
When compiled with
gcc -Wall -pedantic -stc=c99
it issued this warning for that line number:
error: ''FD_SET'' undeclared (first use in this function)
There''s no argument that the line of code was wrong. I am curious
though why a compiler would choose to emit that particular message.
It was most confusing since FD_SET calls preceded and followed this one,
and they were not generating these "undeclared" warnings.
Regards,
David Mathog
David Mathog wrote:There was an editing error in one of my programs giving this line (two
left parentheses, one right):
FD_SET((ncmd->cmd_in_fd,&read_set);
When compiled with
gcc -Wall -pedantic -stc=c99
it issued this warning for that line number:
error: ''FD_SET'' undeclared (first use in this function)
There''s no argument that the line of code was wrong. I am curious
though why a compiler would choose to emit that particular message.
It was most confusing since FD_SET calls preceded and followed this one,
and they were not generating these "undeclared" warnings.How is FD_SET defined?
In article <fk**********@naig.caltech.edu>,
David Mathog <ma****@caltech.eduwrote:>There was an editing error in one of my programs giving this line (two
left parentheses, one right):
FD_SET((ncmd->cmd_in_fd,&read_set);
>When compiled with
gcc -Wall -pedantic -stc=c99
>it issued this warning for that line number:
error: ''FD_SET'' undeclared (first use in this function)
>There''s no argument that the line of code was wrong. I am curious
though why a compiler would choose to emit that particular message.
It was most confusing since FD_SET calls preceded and followed this one,
and they were not generating these "undeclared" warnings.Suppose FD_SET is an object-like macro, then because of the missing
bracket, the line is not an object-like invocation of the macro
and so FD_SET would not be recognized as a macro name on that line.
--
So you found your solution
What will be your last contribution?
-- Supertramp (Fool''s Overture)
ro******@ibd.nrc-cnrc.gc.ca (Walter Roberson) writes:
In article <fk**********@naig.caltech.edu>,
David Mathog <ma****@caltech.eduwrote:>>There was an editing error in one of my programs giving this line (two
left parentheses, one right):
> FD_SET((ncmd->cmd_in_fd,&read_set);
>>When compiled with
> gcc -Wall -pedantic -stc=c99
>>it issued this warning for that line number:
> error: ''FD_SET'' undeclared (first use in this function)
>>There''s no argument that the line of code was wrong. I am curious
though why a compiler would choose to emit that particular message.
It was most confusing since FD_SET calls preceded and followed this one,
and they were not generating these "undeclared" warnings.
Suppose FD_SET is an object-like macro, then because of the missing
bracket, the line is not an object-like invocation of the macro
and so FD_SET would not be recognized as a macro name on that line.That doesn''t make sense. To be expanded, an object-like macro
doesn''t need to be followed by any particular token. And if you
actually meant function-like macro, then the preprocessor would
continue reading the arguments from succeeding lines of the
source file; the lack of a right parenthesis on the same line
would not dissuade it from the idea that it was expanding a
macro.
--
"In My Egotistical Opinion, most people''s C programs should be indented six
feet downward and covered with dirt." -- Blair P. Houghton
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