如何在OpenCV FileStorage的XML嵌套节点中写入值？

I want to write multiple values (Value_1,…,Value_N) into nested nodes of an XML file using OpenCV::FileStorage, targeting the following XML structure:

<?xml version="1.0"?>
<opencv_storage>
    <A>
        <B>
            <Value_1>1</Value_1>
            …
            <Value_N>N</Value_N>
        </B>
    </A>
</opencv_storage>

What's the correct C++ code to achieve this? Also, is the following approach feasible?

FileStorage fs(file, FileStorage::APPEND);
fs << "A->B->Value_1" << 1; // ???
…
fs << "A->B->Value_N" << N; // ???

First off, that A->B->Value_X syntax won't work with OpenCV's FileStorage. The API doesn't support path-style direct access to nested nodes like that — you have to explicitly open and close each nested node using curly braces { and } to define the hierarchy.

Here's the correct C++ code to generate your target XML structure:

#include <opencv2/opencv.hpp>
#include <string>
#include <iostream>

int main() {
    const int N = 5; // Replace with your actual number of values
    const std::string file_path = "output.xml";

    // Open FileStorage in WRITE mode (creates new file, overwrites if exists)
    // Use FileStorage::APPEND only if you need to add to a valid existing OpenCV XML
    cv::FileStorage fs(file_path, cv::FileStorage::WRITE);

    if (!fs.isOpened()) {
        std::cerr << "Failed to open file for writing!" << std::endl;
        return -1;
    }

    // Start the <A> node
    fs << "A" << "{";
        // Start the <B> node inside <A>
        fs << "B" << "{";
            // Write Value_1 to Value_N dynamically
            for (int i = 1; i <= N; ++i) {
                std::string value_key = "Value_" + std::to_string(i);
                fs << value_key << i;
            }
        // Close the <B> node
        fs << "}";
    // Close the <A> node
    fs << "}";

    // FileStorage auto-closes when it goes out of scope, but you can call fs.release() explicitly if needed
    return 0;
}

Key Details: #

• Node Hierarchy Control: The curly braces { and } are how FileStorage identifies nested nodes. You open a node with "{" and must close it with "}" to maintain valid XML structure.
• Mode Selection: Use cv::FileStorage::WRITE for creating a new file. If you need to append to an existing valid OpenCV XML, use FileStorage::APPEND — but note that appending requires you to first navigate to the existing <A><B> node (you'd need to read the existing structure first to modify it safely).
• Dynamic Key Generation: The loop uses std::to_string to create the Value_X keys on the fly, which is ideal if your N value is variable.

If your goal was to append values to an already existing <A><B> node (rather than creating it from scratch), you'd need to read the entire existing file into a data structure, add the new values, then write the updated structure back — OpenCV's FileStorage doesn't support direct in-place appending to nested nodes via a path shortcut.

内容的提问来源于stack exchange，提问作者N.R.