linux I/O函数使用

#include <sys/types.h>
#include <unistd.h>
off_t lseek(int fd, off_t offset, int whence);

#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>

#define BUFFER_SIZE 1024
#define SRC_FILE_NAME "src_file"
#define DEST_FILE_NAME "dest_file"
//根据传入的参数来设置offset
#define OFFSET (atoi(args[1])) 

int main(int argc, char*args[]) {
    int src_file, dest_file;
    unsigned char buff[BUFFER_SIZE];
    int real_read_len, off_set;
    if (argc != 2) {
        fprintf(stderr, "Usage: %s offset\n", args[0]);
        exit(-1);
    }
    src_file = open(SRC_FILE_NAME, O_RDONLY);
    dest_file = open(DEST_FILE_NAME, O_WRONLY | O_CREAT, S_IREAD | S_IWRITE );//owner权限：rw
    if (src_file < 0 || dest_file < 0) {
        fprintf(stderr, "Open file error!\n");
        exit(1);
    }
    off_set = lseek(src_file, -OFFSET, SEEK_END);//注意，这里对offset取了相反数
    printf("lseek() reposisiton the file offset of src_file: %d\n", off_set);
    while((real_read_len = read(src_file, buff, sizeof(buff))) > 0) {
        write(dest_file, buff, real_read_len);
    }
    close(dest_file);
    close(src_file);
    return 0;
}
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作者：Sino_Crazy_Snail 
来源：CSDN 
原文：https://blog.csdn.net/Sino_Crazy_Snail/article/details/80777316 
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