C语言程序设计（第2版）课件 蔺德军16 文件

文件

本章主要内容文件类别及打开方式文件打开文件关闭fputcfgetc函数freadfwrite函数fprintffscanf函数文件指针定位文件类别及打开方式文件类别:ASCII文件(文本),二进制文件文件处理过程1.打开2.读写3.关闭文本文件与二进制文件区别文件打开打开函数:FILE*fopen(文件名,读写方式)打开成功返回文件指针,否则返回空指针文件名和读写方式都是字符串,如:FILE*fp;fp=fopen(“C:\\f1.txt”,”r”)读写方式:组合:r,w,a,r+,w+,a+,rb,wb,ab,rb+,wb+,ab+文件关闭读写文件的内容,是先放在缓冲区内,在关闭文件时,内容才真正被写入磁盘文件,因此一个文件没有正常关闭,可能会丢失数据文件关闭函数intfclose(FILE*fp);正常关闭返回0，关闭失败返回非0值文件结束判断：intfeof(FILE*fp);//到达文件末尾返回1,否则返回0也可以通过读出的字符判断,文件结束字符ASCII值为-1或0xff文件存在判断函数，在IO.H中：intaccess(char*filename,intmode);成功返回0否则返回-1mode0存在；1执行；2写，4读，6读写；读写字符fputc,fgetc格式:intfputc(intch,FILE*fp);

intfgetc(FILE*fp);成功返回读写值，不成功返回-1；例#include<stdio.h>#include<process.h>intmain(){chari,c;FILE*fpr,*fpw;fpw=fopen("c:\\tt\\text1.txt","w");if(fpw==NULL){printf("openerror");exit(0);}for(i='a';i<='z';i++)fputc(i,fpw);fclose(fpw);fpr=fopen("c:\\tt\\text1.txt","r");fpr=fopen("c:\\tt\\text2.txt","w");if((fpw==NULL)||(fpr==NULL)){printf("openerror");exit(0);}while(!feof(fpr)){c=fgetc(fpr);fputc(c+3,fpw);}fclose(fpr);fclose(fpw);}在一个文件内写入a~z26个字符,然后读出,把每个字符ASCII加3后写入另一个文件fwrite、freadunsignedfwrite(void*buffer,unsignedsize,unsignedcount,FILE*fp)unsignedfread(void*buffer,unsignedsize,unsignedcount,FILE*fp)四个参数分别是:存放数据首地址,每个单元字节数,读写多少个单元,读写文件指针fwrite、fread举例#include<stdio.h>typedefstructstudent{intno,age;};studentst;intmain(){inti;FILE*fp;fp=fopen("c:\\rr.dat","wb");for(i=0;i<3;i++){cout<<"another\n";scanf("%d%d",&st.no,&st.age);fwrite(&st,sizeof(st),1,fp);}fclose(fp);fp=fopen("c:\\rr.dat","rb");while(!feof(fp)){fread(&st,sizeof(st),1,fp);if(!feof(fp))printf("no:%d,age,%d\n",st.no,st.age);}fclose(fp);}fprintf、fscanffprintf(FILE*fp,char*format,args);fscanf(FILE*fp,char*format,args);函数使用和printfscanf相似,只能读写ASCII文件fprintffscanf举例//查看写的文件，找出错原因#include<stdio.h>intmain(){ FILE*fp; inta,b; fp=fopen("D:\\t\\tf.txt","w"); scanf("%d%d",&a,&b);//输入23 fprintf(fp,"%d%d",a,b);//文件内23成一个数 fclose(fp); fp=fopen("D:\\t\\tf.txt","r"); fscanf(fp,"%d%d",&a,&b); fclose(fp); printf("a=%d,b=%d\n",a,b); }fgets、fputschar*

fgets(char*s,intlen,FILE*fp);intfputs(char*s,FILE*fp);

文件指针定位正常读写过程中，文件指针自动下移,移到下一次应读写的位置也可以使用文件指针移动函数,人为移动文件指针voidrewind(FILE*fp)使文件指针指向文件开头intfseek(FILE*fp,longoffset,intbase);从base移动offset个字节,正值向后移,负值向前移,移动成功返回1，否则返回非0base值可选项:SEEK_SET(文件头)SEEK_CUR(当前指针位置)SEEK_END(文件尾)辅助函数:longftell(FILE*fp);获得文件指针当前位置文件指针定位文件随机读写示例#include<stdio.h>#include<process.h>#include<string.h>structstudent{intid;charname[10];}st1;intmain(){intno=0,n;charname[10];FILE*fp;fp=fopen("c:\\tmp1.txt","wb+");if(NULL==fp){printf("openerror");exit(0);}while(no!=-1){scanf("%d%s",&no,name);st1.id=no;strcpy(,name);if(st1.id!=-1)fwrite(&st1,sizeof(st1),1,fp);};rewind(fp);while(!feof(fp)){fread(&st1,sizeof(st1),1,fp);if(!feof(fp))printf("%d%s\n",st1.id,);}rewind(fp);n=0;while(n!=-1){printf("seekNo?");

scanf("%d",&n);if(n!=-1){if(fseek(fp,(n-1)*sizeof(st1),SEEK_SET)==0){printf("%d\n",ftell(fp));fread(&st1,sizeof(st1),1,fp);printf("%d%s\n",st1.id,);}}elseprintf("notfind\n");}fclose(fp);}修改记录举例#include<stdio.h>#include<process.h>#include<string.h>structstudent{intid;charname[10];}st1;voidCreateFile(char*FileName){ intno=0;charname[10];FILE*fp;fp=fopen(FileName,"wb");if(NULL==fp){printf("openerror");exit(0);}while(no!=-1) {scanf("%d%s",&no,name);st1.id=no;strcpy(,name);if(st1.id!=-1)fwrite(&st1,sizeof(st1),1,fp); }; fclose(fp);}voidShowFile(char*FileName){FILE*fp;fp=fopen(FileName,"rb");while(!feof(fp)){fread(&st1,sizeof(st1),1,fp);if(!feof(fp))printf("%d%s\n",st1.id,);}fclose(fp);}voidChangeByRecNo(inti,intid,char*name,char*FileName)//根据记录号改{FILE*fp;fp=fopen(FileName,"rb+");fseek(fp,(i-1)*sizeof(st1),SEEK_SET);st1.id=id;strcpy(,name);//printf("now%d%s\n",st1.id,);fwrite(&st1,sizeof(st1),1,fp);fclose(fp);}voidChangeByID(intid,char*name,char*FileName)//根据no改{FILE*fp;fp=fopen(FileName,"rb+");while(!feof(fp)){fread(&st1,sizeof(st1),1,fp);//printf("r%d%s\n",st1.id,);if(st1.id==id) { //printf("find%d%s\n",st1.id,); strcpy(,name); fseek(fp,-sizeof(st1),SEEK_CUR);