Bsearch和垃圾中的值的比較函數

Question

我有以下程序：

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

#define DICT_BUFSIZE 64 

int compar(const void * a, const void * b) 
{ 
    const char* c1 = (const char*)a; 
    const char* c2 = (const char*)b; 

    printf("c1: %s | c2: %s\n", c1, c2); 

    return strcmp(c1, c2); 
} 

int main (void) 
{ 
    FILE*  fdict; 
    uint32_t i; 
    char** dict = NULL; 
    size_t size = 0; 
    size_t size_alloced = 0; 
    char  buf[DICT_BUFSIZE]; 

    fdict = fopen("/usr/share/dict/words", "r"); 
    if (!fdict) { 
     printf("Could not open \"%s\": %s\n", "usr/share/dict/words", strerror(errno)); 
     exit(1); 
    } 

    for (i = 0; fgets(buf, DICT_BUFSIZE, fdict); ++i) { 
     size_t len; 

     if (i == size_alloced) { 
      dict = realloc(dict, (i +50000) * sizeof(*dict)); 
      size_alloced += 50000; 
     } 
     len = strlen(buf); 
     dict[i] = malloc(len); 

     memcpy(dict[i], buf, len -1); 
     dict[i][len -1] = '\0'; 
    } 
    size = i; 

    //for (i = 0; i < size; i++) 
     //printf("%s\n", dict[i]); 

    if(bsearch("company", dict, size, sizeof(*dict), compar)) 
     printf("Found!\n"); 

    for (i = 0; i < size; ++i) 
     free(dict[i]); 
    free(dict); 

    fclose(fdict); 

    return 0; 
} 

在（要搜索的鍵）中的「C1」可變的「COMPAR」功能被正確地顯示，但有垃圾輸出在v2變量中。

下面是一個示例輸出：

c1: company | c2: ��� 
c1: company | c2: �$z 
c1: company | c2: ��I 
c1: company | c2: ��7 
c1: company | c2: P�. 
c1: company | c2: �b3 
c1: company | c2: �1 
c1: company | c2: P�/ 
c1: company | c2: ��0 
c1: company | c2: PC0 
c1: company | c2: @g0 
c1: company | c2: y0 
c1: company | c2: 0�0 
c1: company | c2: ��0 
c1: company | c2: `�0 
c1: company | c2: ��0 
c1: company | c2: 
c1: company | c2: P�0 

我無法理解這種行爲。

Answer 1

如果您正在搜索int的數組，您將會將const void *參數轉換爲您的比較函數int *，您會不會？

您正在搜索的char *數組，所以你需要轉換const void *參數char ** - 你需要傳遞一個char **論據被發現的價值。

需要對你的代碼的變化是最小的，但是至關重要的：

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

#define DICT_BUFSIZE 64 

static int compar(const void *a, const void *b) 
{ 
    const char *c1 = *(const char **)a; 
    const char *c2 = *(const char **)b; 

    printf("c1: %s | c2: %s\n", c1, c2); 

    return strcmp(c1, c2); 
} 

int main (void) 
{ 
    FILE*  fdict; 
    uint32_t i; 
    char** dict = NULL; 
    size_t size = 0; 
    size_t size_alloced = 0; 
    char  buf[DICT_BUFSIZE]; 
    const char *file = "/usr/share/dict/words"; 

    fdict = fopen(file, "r"); 
    if (!fdict) { 
     printf("Could not open \"%s\": %s\n", file, strerror(errno)); 
     exit(1); 
    } 

    for (i = 0; fgets(buf, DICT_BUFSIZE, fdict); ++i) { 
     size_t len; 

     if (i == size_alloced) { 
      dict = realloc(dict, (i +50000) * sizeof(*dict)); 
      size_alloced += 50000; 
     } 
     len = strlen(buf); 
     dict[i] = malloc(len); 

     memcpy(dict[i], buf, len -1); 
     dict[i][len -1] = '\0'; 
    } 
    size = i; 

    //for (i = 0; i < size; i++) 
     //printf("%s\n", dict[i]); 

    const char *search = "company"; 
    if(bsearch(&search, dict, size, sizeof(*dict), compar)) 
     printf("Found!\n"); 

    for (i = 0; i < size; ++i) 
     free(dict[i]); 
    free(dict); 

    fclose(fdict); 

    return 0; 
} 

比較函數現在需要兩個char **值，並捕獲字符串的每個點來。

該調用的第一個參數需要爲變量char *的地址;因此增加了變量const char *search = "company";。

一些清理包括使比較函數靜態（主要是爲了滿足我的迂腐默認編譯選項 - 雖然最好在函數被定義之前聲明），並且使用變量const char *file = "/usr/share/dict/words";來避免（接近）重複到fopen()和錯誤信息。

樣本輸出（和MacOS塞拉利昂10.12.3在Mac上運行）：

c1: company | c2: modifier 
c1: company | c2: eagle 
c1: company | c2: Canarian 
c1: company | c2: counteridea 
c1: company | c2: citropten 
c1: company | c2: compulsoriness 
c1: company | c2: coelenteric 
c1: company | c2: Colossian 
c1: company | c2: commonable 
c1: company | c2: compilation 
c1: company | c2: compagination 
c1: company | c2: compatriot 
c1: company | c2: comparition 
c1: company | c2: comparable 
c1: company | c2: companionate 
c1: company | c2: companionway 
c1: company | c2: comparability 
c1: company | c2: company 
Found!