C语言程序设计课件英文Cprogramla.ppt

1、LOGOChapter Seven FileFileChapter SevenContents Introduction1Open/close file2Read/write file 3 Check the state of the opening file4The location of the file pointer54Chapter SevenHow to get the data while run a program?Where will the result in?How can input the result of a program to another program?

2、Introduction The procedure of C language EditLinkCompile Chapter Seven Introductionprogram format outputcharacter outputstring outputinitializationassignment input from keyboardmemorymemoryformat inputcharacter inputstring input Read data from a file Write data to a fileChapter Seven Introduction Fi

3、le is the gather of related information saved in memory device(assistant memory)OS manages system in files Processing files means file input/out processing.Procedure 1 open file2 file read/write 3 close file.Interface input/out devices are treated as files in C.File accessing methods:1)Buffered I/O(

4、or stream I/O)2)Unbuffered I/O(or low-level I/O)Chapter Seven IntroductionBuffered (temporary storage location)Well discuss Buffered I/O in our lecture In buffered I/O,-open a communication area in RAMDISkPROGRAMOutput file buffer Input file bufferThere are two ways to deal with file:Binary fileASCI

5、I file Chapter Seven Introduction Stream is the abstract of file used to deal with file.There are two kinds of streams in C.The character is ASCII code.one ASCII code occupies one byte,new line n is end of line.After read/write a character from/to ASCII file,the fp increases automatically to guarant

6、ee the read/write sequences.Text streamBinary streamStoring data to disk in the form the same as in RAM.Example:10000 In binary file,use 2 bytes In ASCII file,use 5 bytesChapter SevenOpen/close fileHow to magange a file in C?PointerOperations open file（load file）operate file using functionsclose fil

7、e （remove file from memory）A file system creat a new filedelete an old oneread/write access a file by its namemanage the memory file usedlimit the users rightChapter SevenOpen/close file File pointer,points to a structure that contains information about the file,such as the location of a buffer,the

8、current character position in the buffer,whether the file is being read or written,and whether errors or end of file have occurred.Users dont need to know the details,because the definitions obtained from include a structure declaration called FILE.I am a student.Chapter Seven 2 The function of open

9、ing a file:FILE*fp;uppercase letters,otherwise,cant be recognized,defined to standard structure,key-word#include is necessary fopen(filename,*mode);stringchar arraychar pointer paths are allowed 1 files pointer:opening a file use function fopen()readwriteappendOpen/close fileChapter SevenOpen/close

10、filefp=fopen(“file.txt”,“r”);open file.txt,read in ASCIIOpening a file means.returns a file pointerspecify the operation to be done points to the first location of file buffer.r-readfile.txtwhich The returned value is assigned to a file pointer.Chapter Seven If process is successful,the returned val

11、ue is a file pointer.(address)FLIE *fp;Otherwise,return NULL pointer.if(fp=fopen(“file.txt”“r”)=NULL)printf(“cant open file n”);exist(1);Open/close fileSymbolExplanationrreadwwriteaappendtText streambBinary stream+Permit read/write If fopen fails,return value is zero(NULL pointer)when:1)fopen wants

12、to open a non existed file for reading.2)read a file not permitted read.3)create a file but disk is full.4)disk sector is bad.Chapter Seven3 Close a fileClose a file opened,argument&a pointer to file to be closed in order to 1)release fp and 2)clean up the buffer.fclose(fp);Open/close file Opened fi

13、le must be closed before ending a program,otherwise,data may be lost.Chapter Seven Writes string into file pointed by stream File read/writefgets(string,n,stream)Reads a string of up to n-1 characters from stream and places them into stringfputs(string,stream)1 read/write file functionsfgetc(fp),fpu

14、tc(fp)read/write a char from/to file read:c=fgetc(fp);read a char from named file.write:fputc(c,fp);write c to named file.Prototype in stdio.h return EOF(-1)if a)at the end of file;b)detecting an error;Using function fgets()and fputs()can realize string input/ouput in files.Chapter Seven main(int ar

15、gc,char*argv )int c;FILE *fpr,*fpd;if(argc!=3)putchar(007);puts(Usage:copy file1,file 2);exit();if(fpr=fopen(argv1,r)=NULL)printf(%c,007);printf(file%s cant open n,argv 1);exit();if(fpd=fopen(argv2,w)=NULL)printf(files%s cant openn ,argv2);exit();while(c=fgetc(fpr)!=EOF)fputc(c,fpd);fclose(fpr);fclo

16、se(fpd);Input three strings(file name)Source file name object file name The function of this program is to copy file1 to file2Chapter Seven#includemain()FILE *fp;char c1；fp=fopen(“file.dat”,”r”)；c1=fgetc(fp);putchar(c1);fclose(fp);#includemain()FILE *fp;char ch=a;fp=fopen(“file.dat”,”w”);fputc(ch,fp

17、);fclose(fp);Read the character from file.dat write character a to file.dat.File read/writefscanf(stream,format,arg,.)Reads data from stream using format conversion specifier into address specifierd by arg.fprintf(stream,format,arg,.)Writes arg into stream using format conversion specifier.Chapter S

18、evenmain()FILE*fp;char*c1=“Turbo C”;char c210;fp=fopen(“file2.dat”,”w”);fputs(c1,fp);fclose(fp);fp=fopen(“file2.dat”,”r”);fgets(c2,8,fp);printf(“%sn”,c2);fclose(fp);File read/write read a string from determined file(fp),have read 7 chars;Returned value:normal the 1st location of the string;error or

19、end of file NULLwrite a string to determined file(fp)Returned value:normal:the number of chars;error:NULLChapter Sevenmain()FILE*fp;char*c1=“Turbo C”;char c210;fp=fopen(“file3.dat”,”w”);fprintf(fp,”%s”,c1);fclose(fp);fp=fopen(“file3.dat”,”r”);fscanf(fp,”%s”,c2);printf(“%sn”,c2);fclose(fp);File read/

20、writeIt is similar to printf,add fp file pointerIt is similar to scanf,add fp file pointerChapter Sevenmain()FILE*fp;char str81,filename80;gets(filename);if(fp=fopen(filename,”w”)=NULL)printf(“can not open this filen”);exit(0);while(strlen(gets(str)0)fputs(str,fp);fputs(“n”,fp);fclose(fp);Input seve

21、ral strings,then save them to diskCan you use“filename”here?How many strings should you input?File read/writeChapter Seven fread reads n items of size length from stream into buffer.File read/write fwrite()/fread()*Two standard library functions are available to facilitate the storage of data arrays

22、 in binary forms.These are fwrite()and fread().fwrite(buffer,size,n,stream);fread(buffer,size,n,stream);buffer:a pointer to the start of the buffer to be written into stream.n:items in the buffer of length size in bytes.Chapter Seven when computer are started,3 standard files are opened automaticall

23、y,and 3 associated file pointers are provided 。User neednt write statements to open standard files and after program are executed,standard files automatically closed.2 Interface input/out devices stdin file inputstdout standard output pointerstderr error exit(1):return to os.Innormal exist exit(0):-

24、normal exist.3 Exit functions program will stop right away.File read/writeChapter SevenThe files state is necessary when using input/out functions,especially testing the end of a file.There are one couple of ways to test the end of file1 EOF When reading/writing ASCII file,EOF is used to test if the

25、 file pointer points to the end of file,if so,the value of EOF is-1 Cant suit for binary file 2 function feof()feof(file pointer name)The return value is nonzero at the end of file,Otherwise ,it is not the end of file .Check the state of the opening file Chapter Sevenwhile(feof(fp)=0)c=fgetc(fp);Che

26、ck the state of the opening file while(c=fgetc(fp)!=EOF)putchar(c );Example:read characters from a file Chapter SevenThe location of he file pointer1 rewind Sets file pointer to stream to beginning of file2 fseek Locates file pointer for stream at offset bytes from origins fseek(file pointer name ，o

27、ffsets，origin）No return value Generally it is Used for binary file0:the begining1:current position 2:the end The number of bytes +move backwards-move forwards return:a zero if the pointer was reset without error.Chapter Seven3、The current position Returns current position of file pointed from stream

28、 Return 1L means there is something wrong The location o f the file pointerWhere is the current position of the file pointer?0 Beginning of file 1 Current position of file pointer 2 End of fileChapter Sevenmain(int argc,char*argv )char s80;int a;FILE *fp;if(fp=fopen(test,w)=NULL)printf(cant open fil

29、e);exit();fscanf(stdin,%s%d,s,&a);/*read from keyboard*/fprintf(fp,%s%d,s,a);/*write to file*/fclose(fp);if(fp=fopen(test,r)=NULL)printf(cant open file);exit();fscanf(fp,%s%d,s,&a);/*read from file*/fprintf(stdout,%s%d,s,a);/*print on screen*/fclose(fp);The location o f the file pointerChapter Seven

30、 /*Writing an array of data using fwrite FWRITE.C*/#include main()static int buffer =70,71,72,73,74,75,76,77,78,79,80,81,82,83 ;FILE*fp;int i;fp=fopen(testdata,w);fwrite(char*)buffer,2,14,fp);fclose(fp);The location o f the file pointerChapter Seven/*fread.c*/#include main()FILE*fp;static int buffer

31、14;int i;fp=fopen(testdata,r);fread(char*)buffer,2,14,fp);fclose(fp);for(i=0;i14;i+)printf(%dn,bufferi);The location o f the file pointerChapter Seven main()static char buffer =abcdefg;long pick;long offset;char c;FILE*fp;fp=fopen(testdata,w);fwrite(buffer,1,7,fp);fclose(fp);fp=fopen(testdata,r);for(pick=3;pick 7;pick+)fseek(fp,pick,0);offset=ftell(fp);fscanf(fp,%c,&c);printf(data item at offset%ld is%cn,offset,c);fclose(fp);The location o f the file pointerLOGO