文章目录
文件描述符重点函数说明copy的实现
文件描述符
所有的I/O操作的系统调用都以文件描述符，一个非负整数(通常是小整数)，来指代打开的文件。
重点函数说明
open函数打开pathname所标识的文件，并返回文件描述文件描述符
#include <sys/stat.h>
#include <fcntl.h>
int open(const char *pathname
, int flags
);
int open(const char *pathname
, int flags
, mode_t mode
);
int creat(const char *pathname
, mode_t mode
);
int openat(int dirfd
, const char *pathname
, int flags
);
int openat(int dirfd
, const char *pathname
, int flags
, mode_t mode
);
read函数，调用从fd所指代的打开的文件中，读取至多count字节的数据，并保存到buf中去
#include <unistd.h>
ssize_t
read(int fd
, void *buf
, size_t count
);
write函数，调用从buf中读取多达count字节数，将数据写入到fd指代的已打开的文件中
#include <unistd.h>
ssize_t
write(int fd
, const void *buf
, size_t count
);
close函数， 关闭已打开的文件描述符 fd
#include <unistd.h>
int close(int fd
);
copy的实现
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#ifndef BUF_SIZE
#define BUF_SIZE 1024
#endif
int main(int argc
, char *argv
[])
{
int inputFd
, outputFd
, openFlags
;
mode_t filePerms
;
ssize_t numRead
;
char buf
[BUF_SIZE
];
if (argc
!= 3 || strcmp(argv
[1], "--help") == 0)
printf("%s old-file new-file\n", argv
[0]);
inputFd
= open(argv
[1], O_RDONLY
);
if (inputFd
== -1)
printf("opening file %s", argv
[1]);
openFlags
= O_CREAT
| O_WRONLY
| O_TRUNC
;
filePerms
= S_IRUSR
| S_IWUSR
| S_IRGRP
| S_IWGRP
|
S_IROTH
| S_IWOTH
;
outputFd
= open(argv
[2], openFlags
, filePerms
);
if (outputFd
== -1)
printf("opening file %s", argv
[2]);
while ((numRead
= read(inputFd
, buf
, BUF_SIZE
)) > 0)
if (write(outputFd
, buf
, numRead
) != numRead
)
printf("couldn't write whole buffer");
if (numRead
== -1)
printf("read");
if (close(inputFd
) == -1)
printf("close input");
if (close(outputFd
) == -1)
printf("close output");
exit(EXIT_SUCCESS
);
}
