gcc在编译lex输出时在printf上给出错误 [英] gcc giving error on printf while compiling lex output

问题描述

对于example.l lex文件，我得到以下错误.如果我注释掉printf，它就会消失.尽管我在lex规范的顶部可以包含%{和%}之间的任意C代码.我需要能够在lex匹配任何内容之前打印一些输出.我所做的事情有什么问题以及如何解决?

For the example.l lex file I get the error below. If I comment out the printf it goes away. I though that the top section of the lex specification could contain any arbitrary C code between the %{ and %}. I need to be able to print some output before lex matches anything. What is wrong with what I have done and how do I fix it?

$ cat example.l 

%{
#include <stdio.h>
printf("foobar\n");
%}

%%

.       ECHO;

$ lex example.l 
$ gcc -g -L/usr/lib/flex-2.5.4a -lfl -o example lex.yy.c
example.l:3: error: expected declaration specifiers or '...' before string constant
example.l:3: warning: data definition has no type or storage class
example.l:3: error: conflicting types for 'printf'
example.l:3: note: a parameter list with an ellipsis can't match an empty parameter name list declaration

推荐答案

如果在这里查看代码，您会发现这里发生了两件事之一……或者您正在函数内部执行#include正文没有意义，或者您在任何函数外部调用printf()，这同样是错误的.

If you look at the code here, you can see that one of two things is happening here ... either you are doing a #include inside a function body which doesn't make sense, or you are calling printf() outside any function, which is equally wrong.

现在，当您考虑到这是flex时，它就是后者.您可能正在拍摄更像这样的东西:

Now, when you take into account this is flex, it's the latter. You were probably shooting for something a little more like this:

%{
#include <stdio.h>
%}

%%

.       ECHO;

%%

int main() {
    printf("foobar\n");
    while (yylex() != 0);
    return 0;
}

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