系统中readt与write区别 fwrite和write的区别
\u8ba1\u7b97\u673a\u539f\u7406\u4e2d write through\u4e0ewrite back\u7684\u533a\u522b\u7ed9\u4f60\u6284\u6765\uff0c\u770b\u662f\u4e0d\u662f\u4f60\u8981\u7684\u3002\u8bed\u53e5\u7b80\u5355\uff0c\u5e94\u5f53\u80fd\u770b\u61c2\uff0c\u4e0d\u6d6a\u8d39\u65f6\u95f4\u62cd\u4e2d\u6587\u4e86\u3002
With Write Through Cache the data is written to both the cache and drive once the data is retrieved. As the data is written to both places, should the information be required it can be retrieved from the cache for faster access. The downside of this method is that the time to carry out a Write operation is greater the time to do a Write to a non cache device. The total Write time is the time to write to the cache plus the time to Write the disk.
With Write Back Cache the write operation does not suffer from the Write time delay. The block of data is initially written to the cache, only when the cache is full or required is the data written to the disk.
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\u800c\u5e26\u7f13\u51b2\u7684I/O\u662f\u6307\u8fdb\u7a0b\u5bf9\u8f93\u5165\u8f93\u51fa\u6d41\u8fdb\u884c\u4e86\u6539\u8fdb\uff0c\u63d0\u4f9b\u4e86\u4e00\u4e2a\u6d41\u7f13\u51b2\uff0c\u5f53\u7528fwrite\u51fd\u6570\u7f51\u78c1\u76d8\u5199\u6570\u636e\u65f6\uff0c\u5148\u628a\u6570\u636e\u5199\u5165\u6d41\u7f13\u51b2\u533a\u4e2d\uff0c\u5f53\u8fbe\u5230\u4e00\u5b9a\u6761\u4ef6\uff0c\u6bd4\u5982\u6d41\u7f13\u51b2\u533a\u6ee1\u4e86\uff0c\u6216\u5237\u65b0\u6d41\u7f13\u51b2\uff0c\u8fd9\u65f6\u5019\u624d\u4f1a\u628a\u6570\u636e\u4e00\u6b21\u9001\u5f80\u5185\u6838\u63d0\u4f9b\u7684\u5757\u7f13\u51b2\uff0c\u518d\u7ecf\u5757\u7f13\u51b2\u5199\u5165\u78c1\u76d8
2、基础知识介绍只介绍LINUX系统函数，常用的有creat,open,close,read,write,lseek,access,一般用于文件编程
3、如何使用谈到如何使用就必须说到另一个知识，文件描述符（file description），是一个非负数。
函数原型：int read(int fd, const void *buf, size_t length)
功能： 从文件描述符fd所指向的文件中读取length个字节到buf所指向的缓存区中，返回值为实际读取的字节数
int write(int fd, const void *buf, size_t length)
功能： 把length个字节从buf所指向的缓存区中写到件描述符fd所指向的文件中，返回值为实际写入的字节数
例子：
#define LENGTH 1024
#define BUFFES_SIZE 1024
int n1, n2;
int fd1, fd2;
int buffer[BUFFES_SIZE];fd1 = open( "HEllo1.txt", O_RDWR | O_CREAT, O_IRUSE | O_IWUSR);
fd2 = open( "HEllo2.txt", O_RDWR | O_CREAT, O_IRUSE | O_IWUSR);
n1 = read( fd1, buffer, LENGTH);
n2 = write( fd2, buffer, n1);
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