std :: ifstream :: open()不起作用

#include<iostream>
#include <fstream>
#include<string>

int main() {
    std::ifstream input_file;
    std::string file_path = "example.txt";

    input_file.open(file_path);

    if (input_file.is_open()) {
        std::string line;
        while (std::getline(input_file, line)) {
            std::cout<< line<< std::endl;
        }
        input_file.close();
    } else {
        std::cout << "Unable to open file: "<< file_path<< std::endl;
    }

    return 0;
}