如果未设置_GNU_SOURCE，如何在flex规则中使用asprintf？

In order to ensure that the asprintf function is visible in the header file <stdio.h>, I have followed the advice of the man page and put:

为了确保在头文件中可以看到asprintf函数，我已经按照手册页的建议放了：

#define _GNU_SOURCE
#include <stdio.h>
// ... uses of asprintf();

This works in normal C programs, although presumably only on GNU/Linux and not on the BSDs.

这适用于普通的C程序，虽然可能只在GNU / Linux上而不在BSD上。

I would like to be able to use the same trick in a flex lexer, e.g.:

我希望能够在flex lexer中使用相同的技巧，例如：

%{
#define _GNU_SOURCE
#include <stdio.h>
%}

%%

\"[^\"].+\" {
  asprintf(&(yylval.string), "%s", yytext);
  return STRING;
}

%%

// ...

but I get a compile warning (implicit-function-declaration) for asprintf.

但是我得到了asprintf的编译警告（implicit-function-declaration）。

Upon further investigation, this is because in the C file that flex generates it includes <stdio.h> before my preamble code, without defining _GNU_SOURCE first.

经过进一步调查，这是因为在flex文件生成的C文件中，我在前导代码之前包含了，而没有先定义_GNU_SOURCE。

How can I write code which uses this function which

如何编写使用此功能的代码

compiles correctly inside flex rules, and
在flex规则中正确编译，和
(optionally) also works in non-GNU environments?
（可选）也适用于非GNU环境？

1 个解决方案

#1

Having re-checked the book that got me into the habit of using asprintf, I have discovered that it is indeed a GNU extension.

重新检查了让我习惯使用asprintf的书，我发现它确实是一个GNU扩展。

It is available in a GCC library called libiberty, which you can use in place of the _GNU_SOURCE macro.

它在名为libiberty的GCC库中可用，您可以使用它来代替_GNU_SOURCE宏。

I was able to install this on Ubuntu 15.10 and Debian 8.2 using:

我可以在Ubuntu 15.10和Debian 8.2上使用以下命令安装：

sudo apt-get install libiberty-dev

I then modified the preamble to include:

然后，我修改了序言，包括：

%{
#include <libiberty/libiberty.h>
%}

and everything worked without any warnings.

一切都没有任何警告。

Assuming that a libiberty package is available for non-Linux distributions (and given that it is part of GCC I would assume this would be the case) this solution should work cross platform (on POSIX-ish OS's.)

假设libiberty软件包可用于非Linux发行版（并且鉴于它是GCC的一部分，我认为会是这种情况），这个解决方案应该跨平台工作（在POSIX-ish操作系统上）。

#1