定义一个c++public类,实现Rs485openreadwriteclose等函数功能
1、要用到unistd.h头文件。
2、 Write函数 用法: write函数所在的头文件为 <unistd.h> write有两种用法。一种是: ssize_twrite(int handle, void *buf, int nbyte); handle 是文件描述符; buf是指定的缓冲区,即指针,指向一段内存单元; nbyte是要写入文件指定的字节数;返回值:写入文档的字节数(成功);-1(出错) write函数把buf中nbyte写入文件描述符handle所指的文档,成功时返回写的字节数,错误时返回-1. 另一种是:write(const char* str,int n) str是字符指针或字符数组,用来存放一个字符串。n是int型数,它用来表示输出显示字符串中字符的个数。 write("string",strlen("string");表示输出字符串常量3、程序示例:
123456789101112131415161718192021222324#include <stdio.h>#include <stdlib.h>#include <fcntl.h>#include <sysstat.h>#include <io.h>#include <string.h>int main(void){int *handle; char string[40];int length, res;/* Create a file named "TEST.$$$" in the current directory and write a string to it. If "TEST.$$$" already exists, it will be overwritten. */if ((handle = open("TEST.$$$", O_WRONLY | O_CREAT | O_TRUNC, S_IREAD | S_IWRITE)) == -1){printf("Error opening file. ");exit(1);}strcpy(string, "Hello, world! ");length = strlen(string);if ((res = write(handle, string, length)) != length){printf("Error writing to the file. ");exit(1);}printf("Wrote %d bytes to the file. ", res);close(handle); return 0; }热门标签: