文章目錄

• • 1 文件操作的封裝
  • • 1.1 代碼實現

1 文件操作的封裝

為了更加方便對文件進行操作，我們這里對系統提供的API進行封裝。主要實現在file_op.h和file_op.cpp中。

1.1 代碼實現

file_op.h：

#ifndef QINIU_LARGE_FILE_OP_H_ #define QINIU_LARGE_FILE_OP_H_#include "common.h"namespace qiniu {namespace largefile{class FileOperation{public:FileOperation(const std::string &file_name, const int open_flags = O_RDWR | O_LARGEFILE);~FileOperation();int open_file();void close_file();int flush_file(); //把文件立即寫入到磁盤int unlink_file(); virtual int pread_file(char *buf, const int32_t nbytes, const int64_t offset);virtual int pwrite_file(const char *buf, const int32_t nbytes, const int64_t offset); int write_file(const char *buf, const int32_t nbytes);//seekint64_t get_file_size();int ftruncate_file(const int64_t length);int seek_file(const int64_t offset);int get_fd() const {return fd_;}protected:int fd_;int open_flags_;char *file_name_;protected:int check_file();protected:static const mode_t OPEN_MODE = 0644;static const int MAX_DISK_TIMES = 5;};} }#endif //QINIU_LARGE_FILE_OP_H_

file_op.cpp：

#include "file_op.h" #include "common.h"namespace qiniu {namespace largefile{FileOperation::FileOperation(const std::string &file_name, const int open_flags):fd_(-1), open_flags_(open_flags){file_name_ = strdup(file_name.c_str());}FileOperation::~FileOperation(){if(fd_ > 0){::close(fd_);}if(NULL != file_name_){free(file_name_);file_name_ = NULL;}}int FileOperation::open_file(){if(fd_ > 0){close(fd_);fd_=-1;}fd_ = ::open(file_name_, open_flags_, OPEN_MODE);if(fd_ < 0){return -errno;}return fd_;}void FileOperation::close_file(){if(fd_ < 0){return;}::close(fd_);fd_ = -1;}int FileOperation::pread_file(char *buf, const int32_t nbytes, const int64_t offset){int32_t left = nbytes;int64_t read_offset = offset;int32_t read_len = 0;char *p_tmp = buf;int i = 0;while( left > 0){++i;if(i >= MAX_DISK_TIMES){break;}if(check_file() < 0){return -errno;}read_len = ::pread64(fd_, p_tmp, left, read_offset);if(read_len < 0){read_len = -errno;if(-read_len == EINTR || EAGAIN == -read_len){continue;}else if(EBADF == -read_len){fd_ = -1;continue;}else {return read_len;}}else if( 0 == read_len){break;}left -= read_len;p_tmp += read_len;read_offset += read_len;}if(0 != left){return EXIT_DISK_OPER_INCOMPLETE;}return TFS_SUCCESS;}int FileOperation::pwrite_file(const char *buf, const int32_t nbytes, const int64_t offset){int32_t left = nbytes;int64_t write_offset = offset;int32_t written_len = 0;const char *p_tmp = buf;int i = 0;while( left > 0){++i;if(i >= MAX_DISK_TIMES){break;}if(check_file() < 0){return -errno;}written_len = ::pwrite64(fd_, p_tmp, left, write_offset);if(written_len < 0){written_len = -errno;if(-written_len == EINTR || EAGAIN == -written_len){continue;}else if(EBADF == -written_len){fd_ = -1;continue;}else {return written_len;}}left -= written_len;p_tmp += written_len;write_offset += written_len;}if(0 != left){return EXIT_DISK_OPER_INCOMPLETE;}return TFS_SUCCESS;}int FileOperation::write_file(const char *buf, const int32_t nbytes){int32_t left = nbytes;int32_t written_len = 0;const char *p_tmp = buf;int i = 0;while( left > 0){++i;if(i >= MAX_DISK_TIMES){break;}if(check_file() < 0){return -errno;}written_len = ::write(fd_, p_tmp, left);if(written_len < 0){written_len = -errno;if(-written_len == EINTR || EAGAIN == -written_len){continue;}else if(EBADF == -written_len){fd_ = -1;continue;}else {return written_len;}}left -= written_len;p_tmp += written_len;}if(0 != left){return EXIT_DISK_OPER_INCOMPLETE;}return TFS_SUCCESS;}int64_t FileOperation::get_file_size(){int fd = check_file();if(fd < 0){return -1;}struct stat statbuf;if( fstat(fd, &statbuf) !=0){return -1;}return statbuf.st_size;}int FileOperation::check_file(){if(fd_ < 0){fd_ = open_file();}return fd_;}int FileOperation::ftruncate_file(const int64_t length){int fd = check_file();if(fd < 0){return fd;}return ftruncate(fd, length);}int FileOperation::seek_file(const int64_t offset){int fd = check_file();if(fd < 0){return fd;}return lseek(fd, offset, SEEK_SET);}int FileOperation::flush_file(){if(open_flags_ & O_SYNC){return 0;}int fd=check_file();if(fd < 0){return fd;}return fsync(fd);}int FileOperation::unlink_file(){close_file();return ::unlink(file_name_);}} }

file_op_test.cpp：

#include "file_op.h" #include "common.h"using namespace std; using namespace qiniu;int main(void){const char * filename = "file_op.txt";largefile::FileOperation *fileOP = new largefile::FileOperation(filename, O_CREAT | O_RDWR | O_LARGEFILE);int fd = fileOP->open_file();if(fd < 0){fprintf(stderr, "open file %s failed. reason: %s\n", filename, strerror(-fd));exit(-1);}char buffer[65];memset(buffer, '8', 64);int ret = fileOP->pwrite_file(buffer, 64, 128);if(ret < 0){if(ret == largefile::EXIT_DISK_OPER_INCOMPLETE){fprintf(stderr, " pwrite_file: read length is less than required!");}else {fprintf(stderr, "pwrite file %s failed. reason: %s\n", filename, strerror(-ret));}}memset(buffer, 0, 64);ret = fileOP->pread_file(buffer, 64, 128);if(ret < 0){if(ret == largefile::EXIT_DISK_OPER_INCOMPLETE){fprintf(stderr, " pread_file: read length is less than required!");}else {fprintf(stderr, "pread file %s failed. reason: %s\n", filename, strerror(-ret));}}else {buffer[64] = '\0';printf("read: %s\n", buffer);}memset(buffer, '9', 64);ret = fileOP->write_file(buffer, 64);if(ret < 0){if(ret == largefile::EXIT_DISK_OPER_INCOMPLETE){fprintf(stderr, " write_file: read length is less than required!");}else{fprintf(stderr, " write_file %s failed. reason: %s\n", filename, strerror(-ret));}}fileOP->close_file();return 0; }

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參考資料：

C/C++從入門到精通-高級程序員之路【奇牛學院】

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