7.2.4文件操作 - 文件操作7.2

7.5FileAccessThegeneralstepsforafileoperation: 1Openthefile 2Dooperationsonthefilebyfilepointer. 3CloseafileInClanguage,filesareaccessedbyfilepointers,whicharedeclaredas: FILE*fp;Duringthefirststep,wecanuseafopentomakefppointstothefilewewanttoaccess. fp=fopen(“data”,“r”); or if((fp=fopen(“data”,”r”))!=NULL)7.5FileAccess

FILE*fopen(char*filename,char*mode); intfclose(FILE*fp);1Thefilenamecanincludefullpath,justlike: fp=fopen(“c:\\system\\t.dat”,”r”);2Themodecanbe “r”:readonly “w”:writeonly “a”:appendonly Ifthesystemdistinguishbetweentextandbinaryfiles,forthelatter,a“b”mustbeappendedtothemodestring. fp=fopen(“t.dat”,”rb”);Whenoperationsfinished,thefileshouldbeclosed.fclose(fp);7.5FileAccess

Functionsusedtoaccessafile:1Readdatafromafile: intgetc(FILE*fp); intfscanf(FILE*fp,char*format,…); intfgets(char*string,intn,FILE*fp); intfread(charbuffer,intsize,intcount,FILE*fp);2Writedataintafile: intputc(intc,FILE*fp); intfprintf(FILE*fp,char*format,…); intfputs(char*string,intn,FILE*fo); intfwrite(char*buffer,intsize,intcount,FILE*fp)3filelocate fseek(FILE*fp,longoff,intstart);7.5FileAccesseg1:filecopy #include<stdio.h> main(intargc,char*argv[]) { FILE*fp1,*fp2; if(argc!=3) { printf(“Usage:copyf1f2\n”); exit(1); } if((fp1=fopen(argv[1],”r”))==NULL||((fp2=fopen(argv[2],”w”))==NULL) { printf(“Can’topenfile!\n”); exit(2); } while(putc(getc(fp1),fp2)!=EOF) ; fclose(fp1); fclose(fp2); }7.5FileAccesseg2:readfromacharacterfile,changelowertoupper. #include<stdio.h> main(intargc,char*argv[]) { FILE*fp1,*fp2; charc; if(argc!=3) exit(1);

if((fp1==fopen(*++argv,”r”))==NULL||((fp2=fopen(*++argv,”w”)=NULL) exit(2); while((c=fgetc(fp1))!=EOF) fputc(c+’A’-’a’,fp2); fclose(fp1); fclose(fp2); }7.5FileAccesseg2:concatenatefiles#include<stdio.h>main(intargc,char*argv[]){ FILE*fp; if(argc==1) filecopy(stdin,stdout); else while(--argc>0) if((fp=fopen(*++argv,”r”))==NULL)｛ printf(“cat:can’topen%s\n”,*argv); return1; }else{ filecopy(fp,stdout); fclose(fp); } return0;}7.5FileAccessvoidfilecopy(FILE*ifp,FILE*ofp){intc;while((c=getc(ifp))!=EOF) putc(c,ofp);}7.6LineInputandOutputchar*fgets(char*line,intmaxline,FILE*fp) fgetsreadnextinputline(includingthenewline)fromfilefpintocharacterarrayline,atmostmaxline-1characterswillberead Theresultlineisterminatedwith‘\0’;intfputs(char*line,FILE*fp) fputswritesastringtoafile(neednotcontainanewline)7.6LineInputandOutputchar*fgets(char*s,intn,FILE*iop){ registerintc; registerchar*cs; cs=s; while(--n>0&&(c=getc(iop))!=EOF) if((*cs++=c)==‘\n’) break; *cs=‘\0’; return(c==EOF&&CS==S)?NULL:s;}intfputs(char*s,FILE*iop){ intc; while(c=*s++) putc(c,iop);

returnferror(ip)?EOF:0;} Datafile问题1：读入n个整数（比如n=10),将其从小到大排序后，存放在一个数据文件中。分别考虑该数据文件是文本形式和二进制形式两种不同情况。问题2：从一个数据文件中读入n个整数（比如n=10),将其从小到大排序后输出，或者存放在另一个数据文件中。分别考虑该数据文件是文本形式和二进制形式两种不同情况。voidsort(int*list,intn){

inti,j,next;

for(i=1;i<n;i++){ next=list[i]; for(j=i-1;j>=0&&next<list[j];j--) list[j+1]=list[j]; list[j+1]=next; }}main(){

intinput[10],i; FILE*fpin,*fpout; if((fpin=fopen("in.dat","r"))==NULL){ printf(“Cannotopenfilein.dat\n”);

exit(-1); } for(i=0;i<10;i++)

fscanf(fpin,"%d",&input[i]); /* fread(input,sizeof(int),10,fpin);*/ sort(input,10); if((fpout=