https://raw.githubusercontent.com/ceph/ceph/master/src/common/safe_io.c

一般而言，用pwrite和pread讀寫磁盤文件不需要用循環，但是在讀寫超大的文件時就一定需要循環，保證正確讀寫

// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*- // vim: ts=8 sw=2 smarttab /** Ceph - scalable distributed file system** Copyright (C) 2011 New Dream Network** This is free software; you can redistribute it and/or* modify it under the terms of the GNU Lesser General Public* License version 2.1, as published by the Free Software* Foundation. See file COPYING.**/#define _XOPEN_SOURCE 500#include <stdio.h> #include <string.h> #include <unistd.h> #include <errno.h> #include <fcntl.h> #include <limits.h>#include "common/safe_io.h" #include "include/compat.h"ssize_t safe_read(int fd, void *buf, size_t count) {size_t cnt = 0;while (cnt < count) {ssize_t r = read(fd, buf, count - cnt);if (r <= 0) {if (r == 0) {// EOFreturn cnt;}if (errno == EINTR)continue;return -errno;}cnt += r;buf = (char *)buf + r;}return cnt; }ssize_t safe_read_exact(int fd, void *buf, size_t count) {ssize_t ret = safe_read(fd, buf, count);if (ret < 0)return ret;if ((size_t)ret != count)return -EDOM;return 0; }ssize_t safe_write(int fd, const void *buf, size_t count) {while (count > 0) {ssize_t r = write(fd, buf, count);if (r < 0) {if (errno == EINTR)continue;return -errno;}count -= r;buf = (char *)buf + r;}return 0; }ssize_t safe_pread(int fd, void *buf, size_t count, off_t offset) {size_t cnt = 0;char *b = (char*)buf;while (cnt < count) {ssize_t r = pread(fd, b + cnt, count - cnt, offset + cnt);if (r <= 0) {if (r == 0) {// EOFreturn cnt;}if (errno == EINTR)continue;return -errno;}cnt += r;}return cnt; }ssize_t safe_pread_exact(int fd, void *buf, size_t count, off_t offset) {ssize_t ret = safe_pread(fd, buf, count, offset);if (ret < 0)return ret;if ((size_t)ret != count)return -EDOM;return 0; }ssize_t safe_pwrite(int fd, const void *buf, size_t count, off_t offset) {while (count > 0) {ssize_t r = pwrite(fd, buf, count, offset);if (r < 0) {if (errno == EINTR)continue;return -errno;}count -= r;buf = (char *)buf + r;offset += r;}return 0; }#ifdef CEPH_HAVE_SPLICE ssize_t safe_splice(int fd_in, loff_t *off_in, int fd_out, loff_t *off_out,size_t len, unsigned int flags) {size_t cnt = 0;while (cnt < len) {ssize_t r = splice(fd_in, off_in, fd_out, off_out, len - cnt, flags);if (r <= 0) {if (r == 0) {// EOFreturn cnt;}if (errno == EINTR)continue;return -errno;}cnt += r;}return cnt; }ssize_t safe_splice_exact(int fd_in, loff_t *off_in, int fd_out,loff_t *off_out, size_t len, unsigned int flags) {ssize_t ret = safe_splice(fd_in, off_in, fd_out, off_out, len, flags);if (ret < 0)return ret;if ((size_t)ret != len)return -EDOM;return 0; } #endifint safe_write_file(const char *base, const char *file,const char *val, size_t vallen) {int ret;char fn[PATH_MAX];char tmp[PATH_MAX];int fd;// does the file already have correct content?char oldval[80];ret = safe_read_file(base, file, oldval, sizeof(oldval));if (ret == (int)vallen && memcmp(oldval, val, vallen) == 0)return 0; // yes.snprintf(fn, sizeof(fn), "%s/%s", base, file);snprintf(tmp, sizeof(tmp), "%s/%s.tmp", base, file);fd = open(tmp, O_WRONLY|O_CREAT|O_TRUNC, 0644);if (fd < 0) {ret = errno;return -ret;}ret = safe_write(fd, val, vallen);if (ret) {VOID_TEMP_FAILURE_RETRY(close(fd));return ret;}ret = fsync(fd);if (ret < 0) ret = -errno;VOID_TEMP_FAILURE_RETRY(close(fd));if (ret < 0) {unlink(tmp);return ret;}ret = rename(tmp, fn);if (ret < 0) {ret = -errno;unlink(tmp);return ret;}fd = open(base, O_RDONLY);if (fd < 0) {ret = -errno;return ret;}ret = fsync(fd);if (ret < 0) ret = -errno;VOID_TEMP_FAILURE_RETRY(close(fd));return ret; }int safe_read_file(const char *base, const char *file,char *val, size_t vallen) {char fn[PATH_MAX];int fd, len;snprintf(fn, sizeof(fn), "%s/%s", base, file);fd = open(fn, O_RDONLY);if (fd < 0) {return -errno;}len = safe_read(fd, val, vallen);if (len < 0) {VOID_TEMP_FAILURE_RETRY(close(fd));return len;}// close sometimes returns errors, but only after write()VOID_TEMP_FAILURE_RETRY(close(fd));return len; }

下面是自己寫的代碼，為了驗證read/writeBlock的正確性，分兩批寫入文件，然后又分兩批讀入文件，實際工程中只要一次讀寫就行了

#include <unistd.h> #include <iostream> #include <stdlib.h> #include <string.h> #include <stdint.h> #include <string> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <fstream> #include <vector> #include <sstream> #include <errno.h>using namespace std;bool writeBlock(int fd, int64_t &fdOft,int8_t *arr, int64_t len) {int64_t num = 0;int64_t oft = 0;int8_t *arr1 = (int8_t*)arr;while (oft < len) {num = pwrite(fd, arr1+oft, len-oft, fdOft+oft);if (num == -1) {return false;}oft += num;}fdOft += oft;return true; }bool readBlock(int fd, int64_t &fdOft, void *arr, int64_t len) {int64_t num = 0;int64_t oft = 0;int8_t *b = (int8_t*)arr;while (oft < len) {num = pread(fd, b + oft, len - oft, fdOft + oft);if (num <= 0) {if (num == 0) {if (oft != len) return false;else return true;}if (errno == EINTR) {continue;//the call was interrupted by a signal befor any data was read}return false;}oft += num;}fdOft += oft;return true; }int main(int argc, char *argv[]) {int64_t len = atol(argv[1]);cout << "len = "<<len <<endl;int fd = open(argv[2], O_RDWR|O_CREAT|O_TRUNC, S_IRWXU);if (fd == -1) {cout << "not open\n";return -1;}int64_t total = sizeof(double)*len;cout << "total = " << total <<endl;double *arr = (double*)malloc(total);if (arr == NULL) {cout << "malloc err\n";return -1;}arr[0] = 0.001;for (int64_t i = 1; i < len; ++i) {arr[i] = arr[i-1] + 0.001;}//int64_t num = pwrite(fd,arr,total,0);int64_t fdOft = 0;int64_t first = total/2;int64_t second = total - first;bool flag = writeBlock(fd, fdOft,(int8_t*)arr, first);if (!flag) {cout << "first no\n";}else {cout << "first yes\n";}flag = writeBlock(fd, fdOft, (int8_t*)arr + first, second);//cout << num<<endl;if (!flag) {cout << "second no\n";}else {cout << "second yes\n";}close(fd);int fdr = open(argv[2], O_RDONLY);double *arr1 = (double*)malloc(total);if (arr1 == NULL) {cout << "malloc error\n";return -1;}int64_t readOft = 0;if (readBlock(fdr, readOft, arr1, first)) {cout << "first read yes\n";}if (readBlock(fdr, readOft, (int8_t*)arr1 + first, second)) {cout << "second read yes\n";}flag = true;for (int64_t i = 0; i < len; ++i) {if (arr1[i] != arr[i]) {flag = false;cout << i << " no equal\n";}}if (flag) cout << "equal\n";close(fdr);return 1; }

總結

以上是生活随笔為你收集整理的linux读写二进制大文件的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。