C语言程序设计新编教程（第2版）答案第9章 文件 习题答案

第9章文件习题答案1.下面的程序有什么问题？intmain(void){int*fp;intk;fp=fopen("gelatin");for(k=0;k<30;k++)fputs(fp,"Nanetteeatsgelatin");fclose("gelatin");return0;}答：因为程序有文件定义，所以应该有#include<stdio.h>。应该把fp声明为文件指针FILE*fp；函数fopen()需要一种模式：fopen(“gelatin”,”w”)或者a模式。Fputs函数中的参数的次序应该反过来，为了清楚，输出字符串应该具有一个换行符，因为fputs并不会自动添加它。Fclose函数需要一个文件指针而不是文件名：fclose(fp)。以下为正确的版本#include<stdio.h>intmain(void){FILE*fp;intk;fp=fopen("gelatin","w");/*用亍创建可冐文件gelatin但赋值给一个文件指针*/for(k=0;k<30;k++)/*循环输出*/fputs("Nanetteeatsgelatin\n",fp);fclose(fp);/*关闭文件*/return0;}2.编写一个程序，将任意数目的字符串写入文件。字符串由键盘输入。#include<stdio.h>#include<stdlib.h>#include<string.h>#include<ctype.h>#defineBUFFER_SIZE50char*read_string(char*buffer,int*pbuffer_size);intmain(void){FILE*pFile=NULL;char*filename="d:\\myfile.txt";charanswer='n';size_tstr_length=0;intbuffer_size=BUFFER_SIZE;char*buffer=malloc(buffer_size);pFile=fopen(filename,"w");if(!pFile){printf("Erroropening%sforwriting.Programterminated.",filename);exit(1);}do{/*从键盘输入字符串*/printf("Enterastring:\n");read_string(buffer,&buffer_size);str_length=strlen(buffer);fwrite(&str_length,sizeof(size_t),1,pFile);fwrite(buffer,str_length,1,pFile);printf("Doyouwanttoenteranother(yorn)?");scanf("%c",&answer);fflush(stdin);}while(tolower(answer)=='y');fclose(pFile);printf("\nFilewritecomplete\n");if(buffer)free(buffer);return0;}/*从键盘读取字符串*//*如果字符串超过buffer文件大小*//*buffer文件自动增加*/char*read_string(char*buffer,int*pbuffer_size){char*temp=NULL;intposition=0;while((buffer[position++]=getchar())!='\n')if(position>=*pbuffer_size-1){/*Increasethesizeofthebuffer*/*pbuffer_size+=BUFFER_SIZE;temp=(char*)malloc(*pbuffer_size);buffer[position]='\0';strcpy(temp,buffer);free(buffer);buffer=temp;temp=NULL;}buffer[position-1]='\0';returnbuffer;}3.编写一个程序，获取用户输入文件名，如存在，则写入从键盘输入的字符串；如不存在，先创建，再获取键盘输入后写入。#include<stdio.h>#include<process.h>main(){ FILE*fp; charfilename[30],str[30];/*定义两个字符型数组*/ printf("pleaseinputfilename:\n"); scanf("%s",filename);/*输入文件名*/ fp=fopen(filename,"w+"); printf("pleaseinputstring:\n");/*提示输入字符串*/ getchar(); gets(str); fputs(str,fp);/*将字符串写入fp所指向的文件中*/ fclose(fp);}4.编写一个文件查看器，它可以将文件显示为十六进制和字符方式。#include<stdio.h>#include<ctype.h>#include<string.h>constintMAXLEN=256;constintDISPLAY=80;constintPAGE_LENGTH=20;intmain(intargc,char*argv[]){charfilename[MAXLEN];FILE*pfile;unsignedcharbuffer[DISPLAY/4-1];intcount=0;intlines=0;inti;if(argc==1){printf("Pleaseenterafilename:");fgets(filename,MAXLEN,stdin);intlen=strlen(filename);if(filename[len-1]=='\n')filename[len-1]='\0';}elsestrcpy(filename,argv[1]);if(!(pfile=fopen(filename,"rb"))){printf("Sorry,can'topen%s",filename);return-1;}while(!feof(pfile)){if(count<sizeofbuffer)buffer[count++]=(unsignedchar)fgetc(pfile);else{for(count=0;count<sizeofbuffer;count++)printf("%02X",buffer[count]);printf("|");for(count=0;count<sizeofbuffer;count++)printf("%c",isprint(buffer[count])?buffer[count]:'.');printf("\n");count=0;if(!(++lines%PAGE_LENGTH))if(getchar()=='E')return0;}}for(i=0;i<sizeofbuffer;i++)if(i<count)printf("%02X",buffer[i]);else