Flex发生C错误:缺少类型说明符? [英] C error with Flex: type specifier missing?

问题描述

在iTerm2 bash中运行以下代码.代码文件是使用Vim创建的.

Running the code below in iTerm2 bash. Code file was created using Vim.

/* just like Unix wc */
%{
 int chars = 0;
 int words = 0;
 int lines = 0;
%}

%%

[a-zA-Z]+  { words++; chars += strlen(yytext); }
\n         { chars++; lines++; }
.          { chars++; }

%%

 main(int argc, char **argv)
{
  yylex();
  printf("%8d%8d%8d\n", lines, words, chars);
}

我运行了命令

$flex fb1-1.1
$cc lex.yy.c -lfl

这是它返回的错误

fb1-1.1:17:1: warning: type specifier missing, defaults to 'int'
  [-Wimplicit-int]
main(int argc, char **argv)
^
1 warning generated.
ld: library not found for -lfl
clang: error: linker command failed with exit code 1 (use -v to see       invocation)

现在可以使用.将main()更改为

Works now. Changed the main() to

int main(int argc, char* argv[])

也将-lfl更改为-ll

Also ran changed -lfl to -ll

$flex fb1-1.1
$cc lex.yy.c -ll
$./a.out
this is a text
^D
1   4    15 

推荐答案

由注释组装而成(因为比查找重复对象更容易):

Assembled from comments (because it was easier than finding a dupe):

1. 在现代C语言(即本世纪的C语言)中，所有函数都需要返回类型，并且 main 仅有的两个合法原型为:

1. In modern C (that is, C from this century), all functions need a return type and the only two legal prototypes for main are:

int main(void)

int main(int argc, char* argv[])

第一种过时的书写方式是 int main().

An obsolescent way to write the first is int main().

在Max OS上，flex发行版不包含 libfl.a .它带有 libl.a .因此，请使用 -ll 而不是 -lfl .但是更好的办法是通过在您的序言中放置以下声明来告诉flex不需要 yywrap 来避免该问题:

On Max OS, the flex distro doesn't include libfl.a. It comes with libl.a. So use -ll instead of -lfl. But much better is to avoid the problem by telling flex not to require yywrap by putting the following declaration in your prologue:

%option noyywrap

更好的方法是使用以下内容:

Even better is to use the following:

%option noinput nounput noyywrap nodefault

在启用警告的情况下进行编译时，

noinput 和 nounput 将避免未使用的功能"警告(应始终这样做). nodefault 告诉flex不要插入默认操作，并在必要时发出警告.默认操作是在stdout上回显不匹配的字符，这通常是不希望的，而且经常造成混淆​​.

noinput and nounput will avoid "unused function" warnings when you compile with warnings enabled (which you should always do). nodefault tells flex to not insert a default action, and to produce a warning if one would be necessary. The default action is to echo the unmatched character on stdout, which is usually undesirable and often confusing.

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