如果c++中文件为空，如何抛出异常？

std::ifstream file(filename);

if (!file.is_open()) {
    throw std::runtime_error("Failed to open file");
}

#include <iostream>
#include <fstream>
#include <stdexcept>

int main() {
    std::string filename = "example.txt";
    std::ifstream file(filename);

    if (!file.is_open()) {
        throw std::runtime_error("Failed to open file");
    }

    // 继续读取文件内容的代码...

    return 0;
}

try {
    // 打开文件并读取内容的代码...
} catch (const std::exception& e) {
    std::cout << "Exception caught: " << e.what() << std::endl;
}