Linux文件非讀寫操作
access()
//檢查是否調用進程有Access這個文件的權限，如果文件是一個符號鏈接，會將它解引用，成功返回0,失敗返回-1設errno
#include <unistd.h>
int access(const char *pathname, int mode);
/*mode(Bitwise Or) :
F_OK //文件是否存在
R_OK //文件是否存在且授予了該進程讀權限
W_OK //文件是否存在且授予了該進程寫權限
X_OK //文件是否存在且授予了該進程執行權限
*/
if(0==access("./a.txt",F_OK))
printf("file exists\n");
if(0==access("./a.txt",R_OK))
printf("file exists and grants read permission\n");
fstat()、stat()、lstat()
//讀取文件狀態,fstat()從fd讀取，stat () i從pathname讀取，lstat()從pathname讀取，如果文件是符號鏈接，則返回符號鏈接本身的信息，而其他的函數會對鏈接解引用
#include<unistd.h>
#include<sys/stat.h>
#include<sys/types.h>
int fstat(int fd, struct stat *buf);
int stat (const char *pathname, struct stat *buf);
int lstat(const char *pathname, struct stat *buf);
/*
struct stat {
dev_t st_dev; /* ID of device containing file */
ino_t st_ino; /* inode number */
mode_t st_mode; /* protection */ //八進制usigned int o%
nlink_t st_nlink; /* number of hard links */
uid_t st_uid; /* user ID of owner */
gid_t st_gid; /* group ID of owner */
dev_t st_rdev; /* device ID (if special file) */
off_t st_size; /* total size, in bytes */ //ld%
blksize_t st_blksize; /* blocksize for filesystem I/O */
blkcnt_t st_blocks; /* number of 512B blocks allocated */
time_t st_atime; /* time of last access */
time_t st_mtime; /* time of last modification */ //ld%,秒
time_t st_ctime; /* time of last status change */
};
一些POSIX宏可以用來檢查文件類型
S_ISREG(m) //is it a regular file? //if yes, return 1
S_ISDIR(m) //is it directory?
S_ISCHR(m) //is it character device?
S_ISBLK(m) //is it block device?
S_ISFIFO(m) //is it FIFO (named pipe)?
S_ISLNK(m) //is it symbolic link? (Not in POSIX.1-1996.)
S_ISSOCK(m) //is it socket? (Not in POSIX.1-1996.)
*/
獲取文件大小
- fseek()把offset移到SEEK_END, 再用ftell()返回文件的大小
- lseek() , 返回文件的大小
3.stat(), struct stat st; st.st_size的數值就是文件大小
#include<unistd.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<stdio.h>
#include<stdlib.h>
#include<time.h>
int main(){
struct stat st={};
int res=stat("./a.txt",&st);
if(-1==res)
printf("stat"),exit(-1);
printf("st_mode=%o,st_size=%ld,st_mtime=%ld\n",st.st_mode,st.st_size,st.st_mtime);
if(S_ISREG(st.st_mode))
printf("Regular file\n");
if(S_ISDIR(st.st_mode))
printf("Dir file\n");
printf("file prot:%o\n",st.st_mode&0777);
printf("file size:%ld\n",st.st_size);
printf("latest modify:%s",ctime(&st.st_mtime));
struct tm* pt=localtime(&st.st_mtime);
printf("latest modify:%d-%d-%d-%02d:%02d:%02d\n",
1900+pt->tm_year,1+pt->tm_mon,pt->tm_mday,pt->tm_hour,pt->tm_min,pt->tm_sec);
//%02輸出2個字符寬度,不足兩位輸出0站位
return 0;
}
chmod()、fchmod():
//更改文件的權限，這兩個函數的唯一區別就是指定文件的方式不一樣，成功返回0，失敗返回-1，設errno
#include <sys/stat.h>
int chmod(const char *path, mode_t mode);
int fchmod(int fd, mode_t mode);
truncate()、ftruncate():
//截斷文件為指定大小，成功返回0,失敗返回-1設errno
#include <unistd.h>
#include <sys/types.h>
int truncate(const char *path, off_t length);
int ftruncate(int fd, off_t length);
/*
如果原大小 > 指定大小，多余的文件數據被丟棄
如果原大小e < 指定大小，文件被擴展，擴展的部分被填充為'\0'
*/
/*-----------------------
* chmod(),truncate();
* -------------------*/
#include<unistd.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<stdlib.h>
int res=chmod("a.txt",0600);
if(-1==res)
perror("chmod"),exit(-1);
int res=truncate("a.txt",100);
if(-1==res)
perror("truncate"),exit(-1);
/*------------------------------------------------------
ftruncate();mmap();結構體指針初始化
----------------------------------------------------*/
#include<unistd.h>
#include<sys/types.h>
#include<fcntl.h>
#include<sys/stat.h>
#include<sys/mman.h>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
typedef struct{
int id;
char name[20];
double salary;
}Emp;
int main(){
int fd=open("./emp.dat",O_RDWR|O_TRUNC|O_CREAT,0664);
if(-1==fd)
perror("open"),exit(-1);
printf("open success\n");
int res=ftruncate(fd,3*sizeof(Emp)); //要用sizeof,且是Emp(類型)不是emp(對象)
if(-1==res)
perror("ftruncate"),exit(-1);
void* pv=mmap(NULL,3*sizeof(Emp),PROT_READ|PROT_WRITE,MAP_SHARED,fd,0);
if((void*)-1==pv)
perror("mmap"),exit(-1);
Emp *pe=pv;
pe[0].id=1001;strcpy(pe[0].name,"zhangfei");pe[0].salary=3000;
pe[1].id=1002;strcpy(pe[1].name,"guanyu");pe[1].salary=3500;
pe[2].id=1003;strcpy(pe[2].name,"liubei");pe[2].salary=4000;
// *(pe+2)={1003,"liubei",4000};
// pe+2->salary=4000; //ATTENTION: ->優先級比+高, 所以一定要加()
printf("map success\n");
res=munmap(pv,3*sizeof(Emp));
if(-1==res)
perror("munmap"),exit(-1);
printf("unmap success\n");
res=close(fd);
if(-1==res)
perror("close"),exit(-1);
printf("close success\n");
return 0;
}
