404错误页面

404错误页面是一种HTTP响应状态码，当用户尝试访问一个不存在的网页时，服务器会返回这个状态码，这种错误页面通常用于告知用户他们正在尝试访问一个不存在的页面，或者是一个已被删除或移动的页面。

在PHP、Java和C++中，我们可以通过编写代码来生成404错误页面，以下是一个简单的示例：

404错误页面

1、PHP:

<?php
header('HTTP/1.1 404 Not Found');
header('Content-Type: text/html; charset=utf-8');
echo '<!DOCTYPE html>';
echo '<html>';
echo '<head>';
echo '<title>404 Not Found</title>';
echo '</head>';
echo '<body>';
echo '<h1>404 Not Found</h1>';
echo '<p>The requested page could not be found.</p>';
echo '</body>';
echo '</html>';
?>

2、Java:

public class HttpErrorHandler implements ServletExceptionHandler {
    public void handle(HttpServletRequest request, HttpServletResponse response) throws ServletException {
        response.setStatus(HttpServletResponse.SC_NOT_FOUND);
        try {
            PrintWriter writer = response.getWriter();
            writer.println("<!DOCTYPE html>");
            writer.println("<html>");
            writer.println("<head>");
            writer.println("<title>404 Not Found</title>");
            writer.println("</head>");
            writer.println("<body>");
            writer.println("<h1>404 Not Found</h1>");
            writer.println("<p>The requested page could not be found.</p>");
            writer.println("</body>");
            writer.println("</html>");
        } finally {
            super.handle(request, response);
        }
    }
}

3、C++:

#include <iostream>
#include <fstream>
#include <string>
int main() {
    std::ifstream file("notfound.html");
    if (!file) {
        std::cerr << "File not found" << std::endl;
        return 1;
    }
    std::string content((std::istreambuf_iterator<char>(file)), std::istreambuf_iterator<char>());
    file.close();
    std::ofstream out("notfound.html");
    if (!out) {
        std::cerr << "Error opening file for writing" << std::endl;
        return 1;
    }
    out << "<!DOCTYPE html>\n" << std::endl;
    out << "<html>\n" << std::endl;
    out << "<head>\n" << std::endl;
    out << "<title>404 Not Found</title>\n" << std::endl;
    out << "</head>\n" << std::endl;
    out << "<body>\n" << std::endl;
    out << "<h1>404 Not Found</h1>\n" << std::endl;
    out << "<p>The requested page could not be found.</p>\n" << std::endl;
    out << "</body>\n" << std::endl;
    out << "</html>\n" << std::endl;
    out.close();
    return 0;
}

这些代码分别实现了PHP、Java和C++的404错误页面，你可以根据需要选择适合你的编程语言来实现这个功能。