从文件中读取指定大小的字节函数read()
 
语法: ssize_t read(int fd,void *buf,int count)
 
说明:
 
         read函数从指定的打开的文件fd中读取指定大小count的字节到从buf开始的缓冲
 
区中.
 
 返回值:若读取失败则返回-1.读取成功则返回实际读取到的字节数,有两种情况:[1].读
 
取到的字节数小于count,这是在读取的文件的总字节数小于count.[2].若读取到的字节
 
数等于count,则在读取的文件的总字节数不小于count时发生.
 
注意:读取到的字节存放在buf缓冲区中,必须最后加上一个字节’\0’才能组成一个字符
 
串.
 
实例:
 
         #include<stdio.h>
         #include<stdlib.h>
         #include<fcntl.h>
         #include<unistd.h>
         #define SIZE 1000
 
         int main(int argc,char *argv[])
         {
               int fd,size;
               char buf[1024];
               if(argc<2)
               {
                      printf(“Usage:%s Filename\n”,argv[0]);
                      exit(1);
               }
               fd=open(argv[1],O_RDONLY);
               if(fd<0)
               {
                      printf(“Fail to open file\n”);
                      exit(2);
                 }
                else
                 {
                       size=read(fd,buf,SIZE);
                       if(size<0)
                        {
                                printf(“Fail to read file\n”);
                                exit(3);
                        }
                       else
                       {
                                printf(“From File %s Read %d bytes\n”,argv[1],size);
                                buf[size]=’\0′;
                                printf(buf);
                        }
                       close(fd);
                   }
                   return 0;
         }