linux,lseek,append用法

打开写的.c文件

内容为

代码

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

//off_t lseek(int fd, off_t offset, int whence);
//int open(const char *pathname, int flags);
//int open(const char *pathname, int flags, mode_t mode);
//ssize_t write(int fd, const void *buf, size_t count);
//ssize_t read(int fd, void *buf, size_t count);
#define filename "mm"
#define writeNum 128
#define readNum 12
int main()
{
        int offset;
        int fd;
        char writeBuff[writeNum] = {0};
        char readBuff[readNum] = {0};
        char *test = "hello world";
        if(writeNum<(strlen(test)+1))
        {

                printf("error:writeBuff less than test\n");
                return -1;
        }
        strcpy(writeBuff,test);

        fd = open("mm",O_APPEND|O_RDWR|O_CREAT,0755);
        if(fd == -1)
        {
                printf("open failed!");
                perror("why");
                return -1;
        }
        printf("open successed!");

//      offset = lseek(fd,1,SEEK_CUR);
        printf("offset is %d\n",offset);
        write(fd,&writeBuff[0],11);
//      read(fd,&readBuff,1);
//      printf("%s \n",readBuff);
        close(fd);
        return 0;




}