从 stderr 重定向到另一个文件描述符

发布于 2024-10-18 21:57:18 字数 1135 浏览 3 评论 0原文

我的程序调用打印到 stderr 的库函数。我想进行干预，以便对文件描述符 #2 的所有写入调用都将被发送到其他地方。

这是我的第一次尝试：

bool redirect_stderr (int fd)
{
    return dup2 (2, fd) > 0;
}

这里，fd 已成功从 open("/foo/bar",O_APPEND|O_CREAT) 获得

，此函数返回 true 后，std::cerr<<" blah" 转到终端而不是文件。

我做错了什么？

谢谢。

更新

谢谢，拉斯曼，但我还没有到那里......

void redirect_stderr_to (const char * output_file)
{
    int fd = open (output_file, O_APPEND | O_CREAT, S_IRUSR | S_IWUSR);

    if (fd < 0) {
        throw RUNTIME_ERROR;
    }
    else {
        if (-1 == dup2 (fd, STDERR_FILENO))
            throw RUNTIME_ERROR;

        std :: cout << (std::cerr ? "Fine\n" : "Bad\n");
        char x [100];
        std :: cerr
            << "Output to " << getcwd (x, 100) << " / " << output_file
            <<  " yields " << fd << " errno: " << errno << "\n";
        std :: cout << (std::cerr ? "Fine\n" : "Bad\n");
    }
}

这输出

Fine
Bad

到标准输出并且给定的文件是空的。（如果不存在则正确创建。）

原文

My program calls library functions which print to stderr. I want to intervene so that all write calls to file descriptor #2 will instead get sent to somewhere else.

Here is my first attempt:

bool redirect_stderr (int fd)
{
    return dup2 (2, fd) > 0;
}

Here, fd was successfully obtained from open("/foo/bar",O_APPEND|O_CREAT)

After this function returns true, std::cerr<<"blah" goes to the terminal and not to the file.

What am I doing wrong?

Thanks.

UPDATE

Thanks, larsmans, but I'm not there yet...

void redirect_stderr_to (const char * output_file)
{
    int fd = open (output_file, O_APPEND | O_CREAT, S_IRUSR | S_IWUSR);

    if (fd < 0) {
        throw RUNTIME_ERROR;
    }
    else {
        if (-1 == dup2 (fd, STDERR_FILENO))
            throw RUNTIME_ERROR;

        std :: cout << (std::cerr ? "Fine\n" : "Bad\n");
        char x [100];
        std :: cerr
            << "Output to " << getcwd (x, 100) << " / " << output_file
            <<  " yields " << fd << " errno: " << errno << "\n";
        std :: cout << (std::cerr ? "Fine\n" : "Bad\n");
    }
}

This outputs