doxgen 中用<table>的写法来绘制3行3列的表格

可以按照以下的方式使用 `<table>` 标签来绘制一个 3 行 3 列的表格：

/**
 * @brief A 3x3 table
 * 
 * +---+---+---+
 * | 1 | 2 | 3 |
 * +---+---+---+
 * | 4 | 5 | 6 |
 * +---+---+---+
 * | 7 | 8 | 9 |
 * +---+---+---+
 */
void table_3x3() {
    std::cout << "+---+---+---+\n";
    std::cout << "| 1 | 2 | 3 |\n";
    std::cout << "+---+---+---+\n";
    std::cout << "| 4 | 5 | 6 |\n";
    std::cout << "+---+---+---+\n";
    std::cout << "| 7 | 8 | 9 |\n";
    std::cout << "+---+---+---+\n";
}

当然，你也可以使用 `<table>` 标签来实现相同的效果：

/**
 * @brief A 3x3 table
 * 
 * <table>
 *   <tr>
 *     <td>1</td>
 *     <td>2</td>
 *     <td>3</td>
 *   </tr>
 *   <tr>
 *     <td>4</td>
 *     <td>5</td>
 *     <td>6</td>
 *   </tr>
 *   <tr>
 *     <td>7</td>
 *     <td>8</td>
 *     <td>9</td>
 *   </tr>
 * </table>
 */
void table_3x3() {
    std::cout << "<table>\n";
    std::cout << "  <tr>\n";
    std::cout << "    <td>1</td>\n";
    std::cout << "    <td>2</td>\n";
    std::cout << "    <td>3</td>\n";
    std::cout << "  </tr>\n";
    std::cout << "  <tr>\n";
    std::cout << "    <td>4</td>\n";
    std::cout << "    <td>5</td>\n";
    std::cout << "    <td>6</td>\n";
    std::cout << "  </tr>\n";
    std::cout << "  <tr>\n";
    std::cout << "    <td>7</td>\n";
    std::cout << "    <td>8</td>\n";
    std::cout << "    <td>9</td>\n";
    std::cout << "  </tr>\n";
    std::cout << "</table>\n";
}

这样使用 `<table>` 标签绘制表格可以更加灵活和方便地控制表格样式，同时也可以方便地进行表格跨行和跨列的合并。