C语言自带的快排和二分查找

Author&＃x1f6b9;:CofCai

Email✉️:cai.dongjun&＃64;nexuslink.cn

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抽时间再详细把C语言标准头文件&＃xff08;库文件&＃xff09;梳理一下。

对于快速排序和二分查找&＃xff0c;其实在C语言中有相应的实现&＃xff0c;在头文件中&＃xff0c;重点是实现cmp函数&＃xff0c;以及理解它内部如何运作的。下面贴出代码&＃xff1a;

/*** author: CofCai* datatime: 2020-12-02 11:20:25* file description:* 该文件是在搜索C语言标准头文件时&＃xff0c;发现在中有* 二分查找和快速排序的函数&＃xff0c;所以遂研究以下。* 二分查找&＃xff1a;* void *bsearch(const void *key, const void *base, size_t n, size_t size, int (*cmp)(const void *keyval, const void *datum));* 快速排序&＃xff1a;* void qsort(void *base, size_t n, size_t size, int (*cmp)(const void *, const void *));* 重点是实现cmp函数&＃xff0c;n是base的个数&＃xff0c;size是base中每个元素的大小&＃xff0c;cmp是对base元素进行操作的函数指针。*/#include
#include
#include void SortAndSearchStringEg();
void SortAndSearchNumEg();int main(int argc, char const *argv[])
{SortAndSearchStringEg();SortAndSearchNumEg();return 0;
}#define TYPE floatint cmp4num(const void* x, const void* y)
{TYPE a, b;a &＃61; *(TYPE*)x;b &＃61; *(TYPE*)y;if (a > b) return 1;else if (a &＃61;&＃61; b) return 0;else return -1;
}void SortAndSearchNumEg()
{TYPE data[] &＃61; {10, 18, 2, 83, 82, 892, 23};TYPE target &＃61; 23;TYPE* get;printf("before quick sort:\n");for (int i &＃61; 0; i < sizeof(data)/sizeof(TYPE); &＃43;&＃43;i){printf("%.f\n", data[i]);}qsort((void*)data, sizeof(data)/sizeof(TYPE), sizeof(TYPE), cmp4num);printf("after quick sort:\n");for (int i &＃61; 0; i < sizeof(data)/sizeof(TYPE); &＃43;&＃43;i){printf("%.f\n", data[i]);}get &＃61; (TYPE*)bsearch((void*)&target, (void*)data, sizeof(data)/sizeof(TYPE), sizeof(TYPE), cmp4num);if (get !&＃61; NULL) {printf("find value %f\n", *get);} else {printf("can&＃39;t find value %f\n", target);}
}int cmp4str(const void* x, const void* y)
{char* str1, *str2;str1 &＃61; (char*)x;str2 &＃61; (char*)y;return strncmp(str1, str2, sizeof(str1)); //升序// return -strncmp(str1, str2, sizeof(str1)); //降序
}#define M 6
#define N 10void SortAndSearchStringEg()
{char str[M][N] &＃61; {"hello","name","cofcai","jackChen","bruceLi","shaby"};char* strtarget &＃61; "hh";char* strfind;printf("before sort:\n");for (int i &＃61; 0; i < M; &＃43;&＃43;i){printf("str[%d] is: %s\n", i, str[i]);}/** 快速排序 */qsort(str, sizeof(str)/(sizeof(char)*N), sizeof(char)*N, cmp4str);printf("after sort:\n");for (int i &＃61; 0; i < M; &＃43;&＃43;i){printf("str[%d] is: %s\n", i, str[i]);}/** 二分查找 */strfind &＃61; (char*)bsearch((const void*)strtarget, str, sizeof(str)/(sizeof(char)*N), sizeof(char)*N, cmp4str);if (strfind !&＃61; NULL) {printf("find str: %s\n", strfind);} else {printf("don&＃39;t find target str: %s\n", strtarget);}
}

结果如下&＃xff1a;