CH5-4 指针 函数 复杂指针

5.11 指向函数的指针_变量

指向函数的指针_变量，可以放入数组、也传递到其他函数、或者由函数返回等。

/*
a) int a; //An integer
b) int *a; //A pointer to an integer
c) int **a; //A pointer to a pointer to an integer
d) int a[10]; //An array of 10 integers
e) int *a[10]; //An array of 10 pointers to integers
f) int (*a)[10]; //A pointer to an array of 10 integers
g) int (*a)(int); //A pointer to a function a that takes
                                        an integer argument and returns an integer
h) int (*a[10])(int); //An array of 10 pointers to functions that
                                                take an integer argument and return an integer
*/
#include <stdio.h>
#include <stdlib.h>
#include < string.h>
//指向函数指针有三个用途：调用函数、数组、做函数的参数。
char* strCompare( char *str1, char *str2){ //每一个函数都有一个入口地址
         return (strcmp(str1, str2) > 0) ? str1 : str2;
}
char* strMaxLength( char *str1, char *str2){
         return strlen(str1) > strlen(str2) ? str1 : str2;
}
int main( int argc, char** argv) {
         char *str1 = "Hello Stone River", *str2 = "Hello World", *result1, *result2;
         char* (*strMax)( void *, void *); //指向函数的指针变量
        strMax = strCompare;    
        result1 = strMax(str1, str2);
        strMax = strMaxLength;
        result2 = strMax(str1, str2);
        printf( "result1 = %s, result2 = %s\n", result1, result2);
         //指针数组，每个数组元素是一个指针变量，将指向一个函数
         char* (*strMaxArray[2])( void *, void *);
        strMaxArray[0] = strCompare;
        strMaxArray[1] = strMaxLength;
        printf( "result1 = %s, result2 = %s\n",
                        strMaxArray[0](str1, str2), strMaxArray[1](str1, str2));
         return (EXIT_SUCCESS);
}

#include <stdio.h>
#include <stdlib.h>
#include < string.h>

#define MAXLINES 500
char *linePT[MAXLINES];

int readLines( char *linePT[], int nLines);
int writeLines( char *linePT[], int nLines);

int numberCMP( char *str1, char *str2){
         double value1, value2;
        value1 = atof(str1); //把字符串转换为float类型
        value2 = atof(str2);
         if(value1 < value2) return -1;
         else if(value1 > value2) return 1;
         else return 0;
}

void swap( void *array[], int i, int j){
         void *tmp;
        tmp = array[i];
        array[i] = array[j];
        array[j] = tmp;
}

void quickSort( void *array[], int left, int right,
                 int (*compare)( void *, void *)){ //指向函数的指针做参数，以方便动态绑定
         int i, last;
         if(left >= right) return;
        swap(array, left, (left + right)/2);
        last = left;
         for(i = left+1; i <= right; i++){
                 if((*compare)(array[i], array[left])) //通过指针调用函数
                        swap(array, ++last, i);
        }
        swap(array, left, last);
        quickSort(array, left, last-1, compare); //迭代调用
        quickSort(array, last+1, right, compare); //迭代调用
}

int main( int argc, char** argv) {
         int nLines;
         int ifNumericSort = 0; //1 if numeric sort
         if(argc > 1 && strcmp(argv[1], "-n") == 0)
                ifNumericSort = 0;
         if(nLines = readLines(linePT, MAXLINES) >= 0){
                quickSort(( void **)linePT, 0, nLines-1, //通过函数向指向函数的指针传地址值
                                ( int (*)( void *, void *))(ifNumericSort ? numberCMP : strcmp));
                 return 0; //指向函数的指针做其他函数的参数
        } else{
                printf( "Input too big to sort\n");
                 return 1;
        }
}

5.12 较复杂指针说明