fd_guard.h

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

// Author: Ge,Jun (gejun@baidu.com)
// Date: Mon. Nov 7 14:47:36 CST 2011

#ifndef BUTIL_FD_GUARD_H
#define BUTIL_FD_GUARD_H

#include <unistd.h>                                  // close()

namespace butil {

// RAII file descriptor.
//
// Example:
//    fd_guard fd1(open(...));
//    if (fd1 < 0) {
//        printf("Fail to open\n");
//        return -1;
//    }
//    if (another-error-happened) {
//        printf("Fail to do sth\n");
//        return -1;   // *** closing fd1 automatically ***
//    }
class fd_guard {
public:
    fd_guard() : _fd(-1) {}
    explicit fd_guard(int fd) : _fd(fd) {}
    
    ~fd_guard() {
        if (_fd >= 0) {
            ::close(_fd);
            _fd = -1;
        }
    }

    // Close current fd and replace with another fd
    void reset(int fd) {
        if (_fd >= 0) {
            ::close(_fd);
            _fd = -1;
        }
        _fd = fd;
    }

    // Set internal fd to -1 and return the value before set.
    int release() {
        const int prev_fd = _fd;
        _fd = -1;
        return prev_fd;
    }
    
    operator int() const { return _fd; }
    
private:
    // Copying this makes no sense.
    fd_guard(const fd_guard&);
    void operator=(const fd_guard&);
    
    int _fd;
};

}  // namespace butil

#endif  // BUTIL_FD_GUARD_H