cartographer源码分析(26)-io-file_writer.h

文件:io/file_writer.h

#ifndef CARTOGRAPHER_IO_FILE_WRITER_H_
#define CARTOGRAPHER_IO_FILE_WRITER_H_

#include <fstream>
#include <functional>
#include <memory>

#include "cartographer/common/port.h"

namespace cartographer {
namespace io {
/*
FileWriter负责文件写入的虚基类,不可拷贝/赋值
没有数据成员.只提供一系列抽象接口.
1),WriteHeader(),写入文件head
2),Write(),写入数据
3),Close(),关闭文件
*/
// Simple abstraction for a file.
class FileWriter {
public:
FileWriter() {}
FileWriter(const FileWriter&) = delete;
FileWriter& operator=(const FileWriter&) = delete;

virtual ~FileWriter() {}

// Write 'data' to the beginning of the file. This is required to overwrite
// fixed size headers which contain the number of points once we actually know
// how many points there are.
virtual bool WriteHeader(const char* data, size_t len) = 0;

virtual bool Write(const char* data, size_t len) = 0;
virtual bool Close() = 0;
};

/*
StreamFileWriter 文件流写入类,继承自FileWriter
数据成员只有一个std::ofstream out_负责将文件写入磁盘

*/
// An Implementation of file using std::ofstream.
class StreamFileWriter : public FileWriter {
public:
~StreamFileWriter() override;

StreamFileWriter(const string& filename);

bool Write(const char* data, size_t len) override;
bool WriteHeader(const char* data, size_t len) override; //从文件开始处写入,覆盖旧数据
bool Close() override;

private:
std::ofstream out_;
};

/*工厂模式,
创建一个FileWriter对象,由智能指针管理生命期,
返回值是std::uniq
4000
ue_ptr<FileWriter>,
函数参数是string.
*/
using FileWriterFactory =
std::function<std::unique_ptr<FileWriter>(const string& filename)>;

}  // namespace io
}  // namespace cartographer

#endif  // CARTOGRAPHER_IO_FILE_WRITER_H_

io/file_writer.cc

#include "cartographer/io/file_writer.h"

namespace cartographer {
namespace io {

//out:File open for writing: the internal stream buffer supports output operations.
//binary:Operations are performed in binary mode rather than text.

StreamFileWriter::StreamFileWriter(const string& filename)
: out_(filename, std::ios::out | std::ios::binary) {}//打开,并以2进制方式写入

StreamFileWriter::~StreamFileWriter() {}

//写入len个char
bool StreamFileWriter::Write(const char* const data, const size_t len) {
if (out_.bad()) {
return false;
}
out_.write(data, len);
return !out_.bad();
}

bool StreamFileWriter::Close() { //关闭文件
if (out_.bad()) {
return false;
}
out_.close();
return !out_.bad();
}

bool StreamFileWriter::WriteHeader(const char* const data, const size_t len) {
if (out_.bad()) {
return false;
}
out_.flush();  //清空buffer
out_.seekp(0); //偏移量为0
return Write(data, len);
}

}  // namespace io
}  // namespace cartographer