5.3.1指向函數(shù)的指針 - 指向函數(shù)的指針5.3

5.11PointerstoFunctionspointerstofunctions:canbeassigned,placedinarrays,passedtofunctions,returnedbyfunctions,…example: #include<stdio.h> #include<string.h> #defineMAXLINES5000/*maxlinestobesorted*/ char*lineptr[MAXLINES];/*pointerstotextlines*/ intreadlines(char*lineptr[],intnlines);

voidqsort(void*lineptr[],intleft,intright,int(*comp)(void*,void*)); intnumcomp(char*,char*); /*sortinputlines*/5.11PointerstoFunctionsmain(intargc,char*argv[]) { intnlines; /*numberofinputlinesread*/ intnumeric=0; /*1ifnumericsort*/ if(argc>1&&strcmp(argv[1],“-n”)==0)numeric=1; if((nlines=readlines(lineptr,MAXLINES))>=0){ qsort((void**)lineptr,0,nlines-1,

(int(*)(void*,void*))(numeric?numcmp:strcmp)); writelines(lineptr,nlines); return0; }else{printf(“inputtoobigtosort\n”); return1; }}5.11PointerstoFunctions/*qsort:sortv[left]…v[right]intoincreasingorder*/voidqsort(void*v[],intleft,intright,int(*comp)(void*,void*)){ inti,last; voidswap(void*v[],intint); 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); qsort(v,left,last-1,comp); qsort(v,last+1,right,comp);}voidswap(void*v[],inti,intj){ void*temp; temp=v[i]; v[i]=v[j]; v[j]=temp;}int*comp(void*,void*))intnumcmp(char*s1,char*s2){doublev1,v2;v1=atof(s1);v2=atof(s2);if(v1<v2)return-1;elseif(v1>v2)return1;elsereturn0;}5.12ComplicatedDeclarationsdeclarationstoworddescriptions:int*f();f:functionreturningpointertointint(*f)()f:pointertofunctionreturningintchar**argvargv:pointertopointertocharint(*daytab)[13]daytab:pointertoarray[13]ofintvoid*comp()comp:functionreturningpointertovoidvoid(*comp)()comp:pointertofunctionreturningvoidchar(*(*x())[])()x:functionreturningpointertoarray[]ofpointertofunctionreturningcharchar(*(*x[3])())[5]x:array[3]ofpointertofunctionreturningpointertoarray[5]ofchar5.12ComplicatedDeclarationsconvertCdeclarationtoaworddescription:grammar:example； （*pfa[])() ( * pfa [] ) () name dir-dcl dir-dcl dcl dir-dcl dir-dcl dcldcl: optional*’sdirect-dcldirect-dcl: name (dcl) direct-dcl() direct-dcl[optionalsize]5.12ComplicatedDeclarationsprogramsthatconvert: /*dcl:parseadeclarator*/ voiddcl(void) { intns; for(ns=0;gettoken()==‘*’;)ns++;/*count*’s*/ dirdcl(); while(ns-->0)strcat(out,“pointerto”); } /*dirdcl:parseadirectdeclaration*/5.12ComplicatedDeclarations voiddirdct(void) {inttype; if(tokentype==‘(‘){ dcl(); if(tokentype!=‘)’)printf(“error:missing)\n); }elseif(tokentype==NAME)strcpy(name,token); elseprintf(“error:expectednameor(dcl)\n”); while((type=gettoken())==PARENS||type==BRACKETS) if(type==PARENS)strcat(out,“functionreturning”); else{strcat(out,“array”); strcat(out,token); strcat(out,“of”); } }5.12ComplicatedDeclarations#include<stdio.h>#include<string.h>#include<ctype.h>#defineMAXTOKEN100enum{NAME,PARENS,BRACKETS};voiddcl(void);voiddirdcl(void);intgettoken(void);inttokentype; /*typeoflasttoken*/5.12ComplicatedDeclarationschartoken[MAXTOKEN];/*lasttokenstring*/charname[MAXTOKEN];/*identifiername*/chardatatype[MAXTOKEN];/*datatype=char,int,ect.*/charout[1000];/*outputstring*/main()/*convertdeclarationtowords*/{ while(gettoken()!=EOF){ /*1sttokenonline*/ strcpy(datatype,token); /*isthedatatype*/ out[0]=‘\0’; dcl(); if(tokentype!=‘\n’)printf(“syntaxerror\n”); printf(“%s:%s\n”,name,out,datatype); } return0;}5.12ComplicatedDeclarationsintgettoken(void) /*returnnexttoken*/{ intc,getch(void); voidungetch(int); char*p=token; while((c=getch())==‘‘||c==‘\t’); if(c==‘(‘){ if((c=getch())==‘)’){ strcpy(token,”()”); returntokentype=PARENS; }else{ungetch(c); returntokentype=‘(‘;} }5.12ComplicatedDeclarationselseif(c==‘[‘){ for(*p++=c;(*p++=getch())!=‘]’;); *p=‘\0’; returntokentype=BRACKETS; }elseif(isalpha(c)){ for(*p++=c;isalnum(c=getch());} *p++=c; *p=‘\0’; ungetch(c); returntokentype=NAME; }elsereturntokentype=c;}5.12ComplicatedDeclarationsundcl:x()*[]*()char==>char(*(*x())[])() /*undcl:convertworddescriptiontodeclaration*/main(){ inttype; chartemp[MAXTOKEN]; while(gettoken()!=EOF){ strcpy(out,token); while((type=gettoken())!=‘\n’) if((type==PARENS||type==BRACKETS) strcat(out,token); e