C++文件操作中如何避免内存泄漏 智能指针管理文件资源实践

#include <iostream>
#include <cstdio>
#include <memory>

int main() {
  // 自定义删除器，用于关闭文件
  auto file_deleter = [](FILE* fp) {
    if (fp) {
      fclose(fp);
      std::cout << "File closed.\n";
    }
  };

  // 使用 unique_ptr 管理 FILE*
  std::unique_ptr<FILE, decltype(file_deleter)> file(fopen("example.txt", "w"), file_deleter);

  if (!file) {
    std::cerr << "Error opening file.\n";
    return 1;
  }

  // 写入数据
  fprintf(file.get(), "Hello, world!\n");

  // unique_ptr 会在离开作用域时自动关闭文件

  return 0;
}

#include <iostream>
#include <cstdio>
#include <memory>
#include <stdexcept>

int main() {
  auto file_deleter = [](FILE* fp) {
    if (fp) {
      fclose(fp);
      std::cout << "File closed.\n";
    }
  };

  try {
    std::unique_ptr<FILE, decltype(file_deleter)> file(fopen("nonexistent.txt", "r"), file_deleter);

    if (!file) {
      throw std::runtime_error("Error opening file.");
    }

    // ... 其他文件操作 ...

  } catch (const std::exception& e) {
    std::cerr << "Exception caught: " << e.what() << std::endl;
    // 文件会在 unique_ptr 析构时自动关闭
    return 1;
  }

  return 0;
}

#include <iostream>
#include <cstdio>
#include <memory>

class FileManager {
public:
  FileManager(const char* filename) : filename_(filename), file_(nullptr, file_deleter) {
    file_.reset(fopen(filename_, "w"));
    if (!file_) {
      throw std::runtime_error("Error opening file.");
    }
  }

  ~FileManager() {
      // file_ 会自动关闭文件
  }

  void writeData(const char* data) {
    if (file_) {
      fprintf(file_.get(), "%s\n", data);
    } else {
      throw std::runtime_error("File is not open.");
    }
  }

private:
  std::string filename_;
  std::unique_ptr<FILE, decltype(file_deleter)> file_;

  static auto file_deleter = [](FILE* fp) {
    if (fp) {
      fclose(fp);
      std::cout << "File closed.\n";
    }
  };
};

int main() {
  try {
    FileManager fm("output.txt");
    fm.writeData("This is some data.");
  } catch (const std::exception& e) {
    std::cerr << "Exception caught: " << e.what() << std::endl;
    return 1;
  }
  return 0;
}

#include <iostream>
#include <cstdio>
#include <memory>

int main() {
  auto file_deleter = [](FILE* fp) {
    if (fp) {
      fclose(fp);
      std::cout << "File closed.\n";
    }
  };

  std::shared_ptr<FILE> file(fopen("shared.txt", "w"), file_deleter);

  if (!file) {
    std::cerr << "Error opening file.\n";
    return 1;
  }

  // 多个 shared_ptr 可以指向同一个文件句柄
  std::shared_ptr<FILE> file2 = file;

  fprintf(file.get(), "Data from file1.\n");
  fprintf(file2.get(), "Data from file2.\n");

  // 当所有 shared_ptr 都被销毁时，文件才会被关闭

  return 0;
}