将Popen（）输出写入文件

发布于 2024-10-12 19:42:07 字数 358 浏览 5 评论 0原文

我一直在尝试从 C++ 调用另一个程序，并将该程序的粗壮内容保存到文本文件中。 popen() 似乎是合适的函数，但将其保存到文本文件不起作用。

      ofstream delaunayfile;
    delaunayfile.open ("triangulation/delaunayedpoints.txt");
      FILE *fp;
      fp = popen("qdelaunay < triangulation/rawpoints.txt", "r");
    delaunayfile << fp;
    delaunayfile.close();

有什么帮助吗？提前致谢！

原文

I've been trying to call another program from c++, and save the stout of that program to a text file. popen() seems to be the appropriate function, but saving it to a text file isn't working.

      ofstream delaunayfile;
    delaunayfile.open ("triangulation/delaunayedpoints.txt");
      FILE *fp;
      fp = popen("qdelaunay < triangulation/rawpoints.txt", "r");
    delaunayfile << fp;
    delaunayfile.close();

Any help? Thanks in advance!

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习ぎ惯性依靠 2024-10-19 19:42:07

您不能将 FILE* 直接写入流中。它将写入内存地址而不是实际的文件内容，因此它不会给您所需的结果。

理想的解决方案是从 ifstream 读取并写入 ofstream，但无法从 构造 ifstream文件*。

但是，我们可以扩展 streambuf 类，使其在 FILE* 上工作，然后将其传递给 istream。快速搜索发现有人已经实现了该功能，并正确命名为 popen_streambuf。请参阅这个具体答案。

然后您的代码将如下所示：

std::ofstream output("triangulation/delaunayedpoints.txt");
popen_streambuf popen_buf;
if (popen_buf.open("qdelaunay < triangulation/rawpoints.txt", "r") == NULL) {
    std::cerr << "Failed to popen." << std::endl;
    return;
}
char buffer[256];
std::istream input(&popen_buf);
while (input.read(buffer, 256)) {
    output << buffer;
}
output.close();

正如 Simon Richter 在评论中指出的，有一个 operator<< ; 接受 streambuf 并将数据写入 ostream 直到到达 EOF。这样，代码将被简化为：

std::ofstream output("triangulation/delaunayedpoints.txt");
popen_streambuf popen_buf;
if (popen_buf.open("qdelaunay < triangulation/rawpoints.txt", "r") == NULL) {
    std::cerr << "Failed to popen." << std::endl;
    return;
}
output << &popen_buf;
output.close();

You cannot write a FILE* directly into a stream. It will write a memory address instead of the actual file contents, therefore it will not give you the desired result.

The ideal solution would be to read from an ifstream and write to your ofstream, but there's no way to construct an ifstream from a FILE*.

However, we can extend the streambuf class, make it work over a FILE*, and then pass it to an istream instead. A quick search revealed someone already implemented that, and properly named popen_streambuf. See this specific answer.

Your code then would look like this:

std::ofstream output("triangulation/delaunayedpoints.txt");
popen_streambuf popen_buf;
if (popen_buf.open("qdelaunay < triangulation/rawpoints.txt", "r") == NULL) {
    std::cerr << "Failed to popen." << std::endl;
    return;
}
char buffer[256];
std::istream input(&popen_buf);
while (input.read(buffer, 256)) {
    output << buffer;
}
output.close();

As pointed by Simon Richter in comments, there's an operator<< that accepts streambuf and writes data to ostream until EOF is reached. This way, the code would be simplified to:

std::ofstream output("triangulation/delaunayedpoints.txt");
popen_streambuf popen_buf;
if (popen_buf.open("qdelaunay < triangulation/rawpoints.txt", "r") == NULL) {
    std::cerr << "Failed to popen." << std::endl;
    return;
}
output << &popen_buf;
output.close();

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你怎么这么可爱啊 2024-10-19 19:42:07

有两种方法可以做到这一点：简单的方法

int rc = system("qdelaunay < triangulation/rawpoints.txt >triangulation/delaunayedpoints.txt");

和稍微复杂的方法，使用 fork()、dup2() 和 execve()，后者无需在系统上安装 shell 解释器即可工作。考虑到这看起来像是你正在做计算工作，我怀疑这不是一个嵌入式系统，所以你可以假设一个工作外壳。

There are two ways to do this: The simple way

int rc = system("qdelaunay < triangulation/rawpoints.txt >triangulation/delaunayedpoints.txt");

and the slightly more elaborate way, using fork(), dup2() and execve(), the latter working without a shell interpreter installed on the system. Given that this looks like you are doing computation work, I suspect this is not an embedded system, so you can assume a working shell.

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