Ç - 检索孩子的退出状态是大于8位 [英] C - Retrieving a child's exit status that is larger than 8 bits

问题描述

注：为简单起见，我不包括太多的错误检查和我的样本code并没有真正起到任何实际目的

Note: For simplicity, I don't include much error checking and my sample code doesn't really serve any practical purpose.

我要什么：

我要那个叉（）一个子进程并已通过调用处理的程序 EXECL（） 。我的父母然后检索退出code为这一进程。这是相当微不足道的。

I want a program that fork()s a child process and has it invoke a process using execl(). My parent then retrieves the exit code for that process. This is fairly trivial.

我的尝试：

int main(int argc, char** argv) {
    int ch = fork();
    if(ch == -1) {
        perror(NULL);
    }else if(ch == 0) {
        // In child, invoke process
        execl("/path/process", "process", 0);
    }else {
        // In parent, retrieve child exit code
        int status = 0;
        wait(&status);
        // print exit status
        if(WIFEXITED(status)) printf("%d\n", WEXITSTATUS(status));
    }
}

我的问题：

WEXITSTATUS（），而我需要从 INT 只检索退出值的低8位>值。具体来说，过程执行计算，结果可能会大于8位。它甚至可能是负的，在这种情况下，最高位将需要重新present正确的值。

WEXITSTATUS() only retrieves the lower 8 bits of the exit value while I need all the bits from the int value. Specifically, process performs a calculation and the result may be larger than 8 bits. It may even be negative, in which case, the highest bit will be needed to represent the correct value.

还有什么我尝试：

另外，当环顾四周，我发现管道（）功能。但是，我不知道如何使用它在这种情况下，因为打完电话后 EXECL（），我不能从孩子中写入一个文件描述符。

Also, while looking around, I found the pipe() function. However, I'm not sure how to use it in this situation since, after calling execl(), I can't write to a file descriptor from within the child.

那么，如何我可以去取回孩子的退出状态是大于8位？

So how can I go about retrieving a child's exit status that is larger than 8 bits?

推荐答案

我不认为你正在尝试完成它是可能的，因为在Linux的（其实我认为这是UX系统），一个进程退出code是一个8位号码（最多256）：0-255（作为一个惯例，0表示成功，其他任何手段误差）和大量的东西，依靠这个事实（包括你使用的宏）。看看下面的一块code的：

I don't think that what you are trying to accomplish it's possible, because in Linux (actually i think it's UX specific), a process exit code is an 8bit number (max 256): 0-255 (and as a convention, 0 means success, anything else means error) and lots of stuff rely on this fact (including the macros you used). Take the following piece of code:

// a.c
int main() {
    return 257;
}

如果您编译它（ GCC AC ），并运行生成的可执行文件（的a.out 的）检查（ ？回声$ ），它的退出code（将要被操作系统截断;嗯或者是它的外壳），它会输出1（约算术包装）：257％256 = 1。

If you compile it (gcc a.c), and run the resulting executable (a.out) checking (echo $?) its exit code (that will be truncated by the OS; hmm or is it the shell?) it will output 1 (wrap around arithmetic): 257 % 256 = 1.

作为替代正如你所说，你可以使用管道（<一个href=\"http://stackoverflow.com/questions/22502124/communication-between-child-and-parent-processes-in-c-linux-parent-process-not\">this后是pretty描述）或插槽（ AF_UNIX 类型）。

As an alternative as you mentioned, you could use pipe (this post is pretty descriptive) or sockets (AF_UNIX type).

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