北京大学计算概论DataFilesSK2007B.ppt

1、Lesson 17 Data Files 2,Hu Junfeng 2007/12/05,2,The Arrangements:,Dynamic Data Structures C+ introduction (part1) C+ introduction (part2) Database introduction (?) Review January 7, the happy ending.,3,Todays objectives,Advanced string operations Random File Access Passing and Returning File Pointers

2、 Binary Files Dynamic Memory Allocation Linked List Basic,4,Reading from Text Files EOF,C appends the low-value hexadecimal byte 0 x00 as the end-of-file (EOF) sentinel when the file is closed EOF sentinel is never counted as part of the file,5,Reading from a Text File (exp.),6,Reading from and Writ

3、ing to Text Files(cont.),Prototypes in stdio.h Examples Examples fgetc(inFile); fgets(message,10,inFile); fscanf(inFile,%lf, fgetc() and fscanf() return EOF when the end-of-file marker is detected fgets() returns a NULL instead,7,Standard Device Files,stdin data stream (read) from keyboard stdout da

4、ta stream (write) from monitor stderr data stream (write) for error message,8,Can be replaced by getchar();,9,Get a line from stream,There are two line-oriented I/O functions, i.e. fgets() and fputs(), which allow us read and write lines instead of chracters. The function prototypes are:char *fgets(

5、char *s, int n, FILE *stream) ;int *fputs(const char *s, FILE *stream);The second argument, n, of fgets() specifies the size of the array in which the string is stored.,10,Prog11.4,11,char * strstr(char *s1, const char *s2);,strstr returns a pointer to the beginning of the sub-string or NULL if not

6、found. Exp: char string1 = “paper tiger; char string2=“tiger; void *pointer; pointer = strstr(string1, string2); ,12,13,char *strtok( char *str1, const char *str2 );,The strtok() function returns a pointer to the next token in str1, where str2 contains the delimiters that determine the token. strtok

7、() returns NULL if no token is found. In order to convert a string to tokens, the first call to strtok() should have str1 point to the string to be tokenized. All calls after this should have str1 be NULL.,14,char *strtok( char *str1, const char *str2 );,15,16,Text to HTML ,17,18,ASP and B/S Archite

8、cture,request,Active server pages,respond,19,Random File Access,fseek(fileName, offset, origin),file stream,File* fp;,program,20,Random File Access,rewind() resets the current position to the start of the file rewind(inFile) fseek() allows the programmer to move to any position in the file fseek(fil

9、eName, offset, origin) Origin: SEEK_SET, SEEK_CUR, and SEEK_END ftell() returns the offset value of the next character that will be read or written ftell(inFile);,21,Random File Access (continued),Examples of fseek() are fseek(inFile,4L,SEEK_SET); fseek(inFile,4L,SEEK_CUR); fseek(inFile,-4L,SEEK_CUR

10、); fseek(inFile,0L,SEEK_SET); fseek(inFile,0L,SEEK_END); fseek(inFile,-10L,SEEK_END);,22,Random File Access (exp),23,Passing and returning file pointer,#include #include FILE *getOpen(); /* function prototype */ void inOut(FILE *); /* function prototype */ int main() FILE *outFile; outFile = getOpen

11、(); inOut(outFile); fclose(outFile); return 0; ,FILE *getOpen() FILE *fpointer; char name13; printf(nEnter a file name: ); gets(name); fpointer = fopen(name,w); if(fname = NULL) printf(nFailed to open the file %s.n, name); exit(1); return(fpointer); ,24,第三次附加作业（可选） 唐诗鉴赏网站的自动生成,要求： 实现方便的诗歌浏览功能。 设计（部分实现）诗歌浏览页面的相关链接