head.h
#ifndef _HEAD_H_ #define _HEAD_H_ #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <stdio.h> #include <string.h> #include <stdlib.h> #include <unistd.h> #include <time.h> #endif
01_open.c
1.open
int open(const char *pathname, int flags); // Open an existing file
int open(const char *pathname, int flags,int mode);//O_CREAT + permissions
Function:
Get a file descriptor
Parameters:
pathname: file name
flags:
Required item: they are mutually exclusive, so there can only be one
O_RDONLY "r"
O_WRONLY
O_RDWR "r+"
Optional:
O_ Create / / create a file. If the file exists, only open it. / / this flag exists, you need to specify the parameter mode
O_TRUNC # file contents empty
O_APPEND mode
/ / later
O_NOCTTY # is not a terminal device
O_ASYNC # asynchronous io, when io is uncertain,
O_NONBLOCK non blocking
Return value:
Successfully returned file descriptor (least recently unused)
Failure Return - 1
open("1.txt",O_WRONLY|O_CREAT,0666);
======================================================================
"r" O_RDONLY
"r+" O_RDWR
"w" O_WRONLY | O_CREAT | O_TRUNC,0064
"w+" O_RDWR | O_CREAT | O_TRUNC,0064
"a" O_WRONLY | O_APPEN | O_CREAT,0064
"a+" O_RDWR | O_APPEN | O_CREAT,0664
2.close
int close(int fd);
Function:
Close file descriptor
#include "head.h"
int main(void)
{
int fd = open("1.txt",O_RDWR | O_CREAT | O_TRUNC,0664);
if(-1 == fd)
{
printf("fail to open.\n");
return -1;
}
printf("fd = %d\n",fd);
close(fd);
return 0;
}02_write.c
3.write
char buf[1024];
ssize_t write(int fd, const void *buf, size_t count);
Function:
Write a string of data to a file through a file descriptor
Parameters:
fd: file descriptor
buf: the first address of the string to be written to the file
count: the number of characters to write
Return value:
Successfully returned the number of actual writes
Failure Return - 1
#include "head.h"
int main(void)
{
int fd = open("1.txt",O_RDWR | O_CREAT | O_TRUNC,0664);
if(-1 == fd)
{
printf("fail to open.\n");
return -1;
}
char buff[] = {"hello world"};
ssize_t ret = write(fd,buff,strlen(buff));
printf("ret = %ld\n",ret);
close(fd);
return 0;
}03_read.c
4.read
ssize_t read(int fd, void *buf, size_t count);
Function:
Read the data in the file through the file descriptor
Parameters:
fd: file descriptor
buf: the first address of the storage data space
count: the number of data to be read
Return value:
Successfully return the number of data read
Failure Return - 1
Return 0 when reading the end of the file
#include "head.h"
int main(void)
{
int fd = open("1.txt",O_RDONLY);
if(-1 == fd)
{
printf("fail to open.\n");
return -1;
}
char buff[1024] = {"lllllllllllllllllllllllllll"};
memset(buff,0,sizeof(buff));//Clear the specified space into the characters you want
ssize_t ret = read(fd,buff,sizeof(buff));
printf("ret = %ld\n",ret);
printf("%s\n",buff);
close(fd);
return 0;
}04_lseek.c
5.lseek
off_t lseek(int fd, off_t offset, int whence);
Function:
Relocating the offset of a file descriptor (file locator)
Parameters:
fd: file descriptor
Offset: offset
Positive: offset backward
Negative: forward offset
Zero: no offset
whence:
SEEK_SET
SEEK_CUR
SEEK_END
Positive cavity
Return value:
Successfully return the value of the current offset (off_t# long int)
Failure Return - 1
off_t len =lseek(fd,0,SEEK_END); // Gets the size of the file
#include"head.h"
int main(int argc, const char *argv[])
{
int fd = open("1.txt",O_RDWR | O_CREAT,0664);
if(-1 == fd)
{
printf("fail to open.\n");
return -1;
}
off_t offset = lseek(fd,3,SEEK_SET);
printf("offset = %ld\n",offset);
write(fd,"A",1);
offset = lseek(fd,4,SEEK_CUR);
printf("offset = %ld\n",offset);
write(fd,"B",1);
offset = lseek(fd,-2,SEEK_END);
printf("offset = %ld\n",offset);
write(fd,"C",1);
offset = lseek(fd,0,SEEK_END);
printf("len = %ld\n",offset);
close(fd);
return 0;
}05_buffer.c
06_fileno.c
1.fileno FILE* fp -> int fd
int fileno(FILE *stream);
Function:
Get a file descriptor in the file stream pointer
Parameters:
Stream: file stream pointer
Return value:
File descriptor returned successfully
Failure Return - 1
#include "head.h"
int main(int argc, const char *argv[])
{
FILE *fp = fopen("1.txt","r+");
int fd = fileno(fp);
write(fd,"hello world",11);
fclose(fp);
return 0;
}07_fdopen.c
2.fdopen int fd -> FILE *fp
FILE *fdopen(int fd, const char *mode);
Function:
Converts a file descriptor to a file stream pointer
Parameters:
fd: open file descriptor
mode:
"r"
"r+"
"w"
"w+"
"a"
"a+"
Return value:
File stream pointer returned successfully
Failure returns NULL
#include "head.h"
int main(int argc, const char *argv[])
{
int fd = open("1.txt",O_RDONLY);
FILE * fp = fdopen(fd,"r");
char buff[1024] = {0};
fgets(buff,sizeof(buff),fp);
printf("%s",buff);
close(fd);
return 0;
}08_time.c
1.time
time_t time(time_t *t);
Function:
Get the number of seconds from January 1, 1970 to now
Parameters:
t: the first address of the storage space for seconds
Return value:
Successfully returned the number of seconds from January 1, 1970 to the present (time_t# long)
Failure Return - 1
time_ Tseconds from January 1, 1970 to now
Calendar time
2.ctime
char *ctime(const time_t *timep);
Function:
Convert seconds to string time
Parameters:
Time: the number of seconds from January 1, 1970 to now
Return value:
First address of time string returned successfully
Failure returns NULL
3.localtime
struct tm *localtime(const time_t *timep);
Function:
Convert seconds to time structure
Parameters:
Time: the first address of the space where the seconds are stored
Return value:
The first address of the space containing the time structure is returned successfully
Failure returns NULL
struct tm {
int tm_sec; /* seconds */
int tm_min; /* minutes */
int tm_hour; /* hours */
int tm_mday; /* day of the month */
int tm_mon; /* month */
int tm_year; /* year */
int tm_wday; /* day of the week */
int tm_yday; /* day in the year */
int tm_isdst; /* daylight saving time */
};
#include "head.h"
int main(int argc, const char *argv[])
{
FILE *fp = fopen("1.txt","w+");
time_t sec = 0;
time(&sec);
// printf("sec = %ld\n",sec);
char *pt = ctime(&sec);
// printf("pt = %s",pt);
struct tm * ptime = localtime(&sec);
printf("%d-%d-%d %d:%d:%d\n",ptime->tm_year+1900,ptime->tm_mon+1,ptime->tm_mday,ptime->tm_hour,ptime->tm_min,ptime->tm_sec);
char buff[1024] = {0};
fgets(buff,sizeof(buff),stdin);
fputs(buff,fp);
return 0;
}09_log.c
#include "head.h"
int main(int argc, const char *argv[])
{
FILE *fp = fopen("log.txt","a");
if(NULL == fp)
{
printf("fail to fopen.\n");
return -1;
}
while(1)
{
char buff[1024] = {0};
fgets(buff,sizeof(buff),stdin);
buff[strlen(buff) - 1] = '\0';
time_t sec;
time(&sec);
struct tm * pt = localtime(&sec);
fprintf(fp,"%s %d-%d-%d %d:%d:%d\n",buff,pt->tm_year+1900,pt->tm_mon+1,pt->tm_mday,pt->tm_hour,pt->tm_min,pt->tm_sec);
fflush(fp);
if(strcmp(buff,"quit") == 0)
{
break;
}
}
fclose(fp);
return 0;
}