文件I/O-open-close

文件描述符

定义

fileno

• 将文件指针转化为文件描述符
  

fdopen

• 将文件描述符转化为文件指针
  

打开或者关闭文件

• <fcntl.h>

open

• <sys/stat.h>:mode_t mode
• <fcntl.h>：int flags
• fail return: -1
  

flag

mode

• <sys/stat.h>
  
  

掩码计算

代码习惯

示例

creat

open和creat等价形式

close

代码习惯

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

int main(void) {
    int fd = -1;
    char * fileName = "./log.txt";

    fd = creat(fileName, 0666);
    if (fd == -1) {
        perror("fail to creat \n");
        exit(EXIT_FAILURE);
    } else {
        printf("create file %s successfully\n", fileName);
    }

    close(fd);
    return 0;
}

/* 
    使用IO系统调用
*/
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>

#ifndef BUF_SIZE
#define BUF_SIZE 1024
#endif

int main(int argc, char * argv[])
{
	int fdInput, fdOutput, iOpenFlags;
	char buf[BUF_SIZE] = {0};
	mode_t FilePerms;
	ssize_t numRead;
	
	
	if (argc != 3 || strcmp(argv[1], "--help") == 0)
	{
		printf("%s old-file new-file\n", argv[0]);
		exit(EXIT_FAILURE);
	}
	
	/* open input and output file */
	fdInput = open(argv[1], O_RDONLY);
	if (fdInput == -1)
	{
		perror("Error open:");
		exit(EXIT_FAILURE);
	}
	
	iOpenFlags = O_CREAT | O_WRONLY | O_TRUNC;
	FilePerms = S_IRUSR | S_IWUSR | S_IRGRP |
				 S_IROTH | S_IWOTH;
	fdOutput = open(argv[2], iOpenFlags, FilePerms);
	if (fdOutput == -1)
	{
		perror("Error open output:");
		exit(EXIT_FAILURE);
	}
	
	/* Transfer data */
	//while ((numRead = read(fdInput, buf, BUF_SIZE)) > 0)	// 两种表示方式皆可
	while ((numRead = read(fdInput, buf, sizeof(buf))) > 0)
	{
		printf("%d\n", numRead);
		if (write(fdOutput, buf, numRead) != numRead)
		{
			perror("Error write:");
			exit(EXIT_FAILURE);
		}
	}
	
	if (numRead == -1)
	{
		perror("Error write:");
		exit(EXIT_FAILURE);
	}
	if (close(fdOutput) == -1)
	{
		perror("Error write:");
		exit(EXIT_FAILURE);
	}
	if (close(fdInput) == -1)
	{
		perror("Error write:");
		exit(EXIT_FAILURE);
	}
	
	exit(EXIT_SUCCESS);
}