C语言read函数

   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;

         }