open，read，write使用实例，文件IO

主要通过运用open，read，write函数实现将txt文件内容复制到另一个txt文件。

#include 
#include 
#include 
#include 
#include 
#include 
#define MAX_READ 99999
int main()
{
 size_t numRead,numWrite;//存储字符串长度
 char buffer[MAX_READ+1];//存储字符串
 printf("please make CPU_usage.txt be copied to target.txt!n");
 int fdin,fdout;//定义两个文件指针，因为要对两个文件实施操作
 //打开和错误判断
 if((fdin=open("CPU_usage.txt",O_RDONLY))==-1)
     {
        printf("source file cannot open!n");
        exit(0);
     }
 
 if ((fdout=open("target.txt", O_WRONLY))==-1)
     {
         printf("target file cannot open!n");
         exit(0);
     }
//read执行成功返回字符串长度
 numRead=read(fdin,buffer,MAX_READ);
 if(numRead==-1)
 {
   printf("read falsen");
         exit(0);
 }
 buffer[numRead]='';//追加结束符
 printf("%s",buffer);
 //成功返回长度
 numWrite=write(fdout,buffer,numRead+1);
 if(numWrite==-1)
 {
  printf("write falsen");
         exit(0);
 }
 printf("copy successnplease check in target.txt:)n");
//关闭文件
     close(fdin);
     close(fdout);
 return 0;
}