练习5-15 增加选项-f，使得排序过程不考虑字母大小写之间的区别。例如比较a和A时认为它们相等

在练习5-14中添加charcmp函数即可

#include <stdio.h>#include <string.h>#define MAXLINES 5000#define NUMERIC  1#define DECR     2#define FOLD     4char *lineptr[MAXLINES];int readlines(char *lineptr[],int nlines);void writelines(char *lineptr[],int nlines,int decr);void qsort2(void *lineptr[],int left,int right,           int (*comp)(void *,void *));int numcmp(char *,char *);int charcmp(char *s,char *t);char option=0;main(int argc,char *argv[]){    int nlines;    int c,rc=0;    while(--argc>0 && (*++argv)[0]=='-')        while(c=*++argv[0]){            switch(c){            case 'n':                option|=NUMERIC;                break;            case 'r':                option|=DECR;                break;            case 'f':                option|=FOLD;                break;            default:                printf("sort: illegal option %c\n",c);                argc=1;                break;            }        }    if(argc)        printf("Usage: sort -nr \n");    else        if((nlines=readlines(lineptr,MAXLINES))>=0){            if(option & NUMERIC)                qsort2((void **)lineptr,0,nlines-1,                       (int (*)(void *,void *))numcmp);/* (int (*)(void *,void *)) */            else if(option & FOLD)                qsort2((void **)lineptr,0,nlines-1,                       (int (*)(void *,void *))charcmp);            else                qsort2((void **)lineptr,0,nlines-1,                       (int (*)(void *,void *))strcmp);            writelines(lineptr,nlines,option & DECR);        }        else{            printf("input too big to sort\n");            rc=-1;        }    return rc;}#define MAXLEN 1000int getline(char *,int);char *alloc(int);int readlines(char *lineptr[],int maxlines){    int len,nlines;    char *p,line[MAXLEN];    nlines=0;    while((len=getline(line,MAXLEN))>0){        if(nlines>MAXLINES || (p=alloc(len))==NULL)            return -1;        else{            line[len-1]='\0';            strcpy(p,line);            lineptr[nlines++]=p;        }    }    return nlines;}int getline(char *s,int lim){    int c;    char *t=s;    while(--lim>0 &&(c=getchar())!=EOF && c!='\n')        *s++=c;    if(c=='\n')        *s++=c;    *s='\0';    return s-t;}#define ALLOCSIZE 10000static char allocbuf[ALLOCSIZE];static char *allocp=allocbuf;char *alloc(int n){    if(allocbuf+ALLOCSIZE-allocp>=n){        allocp+=n;        return allocp-n;    }    else        return 0;}void writelines(char *lineptr[],int nlines,int decr){    int i;    if(decr)        for(i=nlines-1;i>=0;i--)            printf("%s\n",lineptr[i]);    else        for(i=0;i<nlines;i++)            printf("%s\n",lineptr[i]);}void qsort2(void *v[],int left,int right,           int (*comp)(void *,void *))//void *v[]{    int i,last;    void swap(void *v[],int,int);    if(left>=right)        return;    swap(v,left,(left+right)/2);    last=left;    for(i=left+1;i<=right;i++)        if((*comp)(v[i],v[left])<0)            swap(v,++last,i);    swap(v,left,last);    qsort2(v,left,last-1,comp);    qsort2(v,last+1,right,comp);}#include <stdlib.h>int numcmp(char *s1,char *s2){    double v1,v2;    v1=atof(s1);    v2=atof(s2);    if(v1<v2)        return -1;    else if(v1>v2)        return 1;    else        return 0;}int charcmp(char *s,char *t){    for(;tolower(*s)==tolower(*t);s++,t++)        if(*s=='\0')            return 0;    return tolower(*s)-tolower(*t);}void swap(void *v[],int i,int j){    void *temp;    temp=v[i];    v[i]=v[j];    v[j]=temp;}