时间戳

首页 > 解决方案 > bsearch 与结构数组

arrays - bsearch 与结构数组

问题描述

我有一个结构数组，已经使用qsort. 我正在尝试在 struct 中搜索名称，但它总是返回NULL。为什么会发生这种情况的解释是什么？

这是我的代码：

#include "card.h"
#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>

int cmpname (const void *pa, const void *pb) {
    const char *p1 = pa;
    const index_t * const *p2 = pb;
    //printf("Comparing: %s %s\n", p1, (char*)*p2);
        return strcmp((p1), (*p2)->name);
}

int main(int argc, char **argv) 
{
    unsigned length;
    int i = 0;
    int length_multiplier = 0;
    char *input = NULL;
    char *pItem;
    index_t **indexs = NULL;
    FILE *input_file;
    
    if((input_file = fopen("index.bin", "rb")) != NULL)
    {
        
        // GETS USER INPUT
        printf(">> ");
        size_t num_read = 0;

        getline(&input, &num_read, stdin); 
        printf("Searching for: %s\n", input);
        if(*input != 113)
        {
            // READING FILE AND ADDING ENTRIES INTO STRUCT
            //int *key;
            //int *pItem;
            //input_file = fopen("index.bin", "rb");
            if (input_file == NULL)
            {
                printf("ERROR OPENING FILE\n");
                free(indexs);
                fclose(input_file);
                return 1;
            }
            // READS THE INPUT FILE
            for(i = 0; fread(&length, sizeof(unsigned int), 1, input_file) != 0; i++)
            {
                length_multiplier++;
                indexs = realloc(indexs, sizeof(index_t *) * length_multiplier);
                indexs[i] = malloc(sizeof(index_t));
        
                indexs[i]->name = malloc(sizeof(char) * length + 1);
                fread(indexs[i]->name, sizeof(char), length, input_file);
                indexs[i]->name[length] = 0;
                fread(&indexs[i]->offset, sizeof(long), 1, input_file);
            }
            for(i = 0; i < length_multiplier; i++)
            {
                printf("%s\n", indexs[i]->name);
            }
            printf("Searching for: %s\n", input);
            
            pItem = (char*) bsearch(&input, indexs, length_multiplier, sizeof(indexs), cmpname);
    
            if(pItem == NULL)
            {
                printf("%s not found\n", pItem);
            }
            else
            {
                printf("found %s\n", pItem);
            }
    
            //FREEING MEMORY
            for(int i = 0; i < length_multiplier; i++)
            {
                free(indexs[i]->name);
                free(indexs[i]);
            }
            free(indexs);
            free(input);
    
            //fread(card[0]->id, sizeof(u_int32_t), 1, input_file);
            fclose(input_file);
    
            return 0;
        }
        else
        {
            printf("Exiting...\n");
            return 1;
        }
    }
    else
    {
        fprintf(stderr, "./parser: cannot open(%s%s%s): No such file or directory", "\"", argv[1], "\"");
        return 1;
    }
        
}

这是我声明的结构：

typedef struct index {
    char *name;
    long offset;
} index_t;

标签： arrayscstructbinary-searchbsearch

解决方案

比较器函数应该比较数组中的两个，而不是两个不同的东西。在你的情况下，你想比较两个index_t *，而不是一个index_t *和一个char *。所以它可能看起来像这样：

int cmpname (const void *pa, const void *pb) {
    const index_t * const *p1 = pa;
    const index_t * const *p2 = pb;
    //printf("Comparing: %s %s\n", p1, (char*)*p2);
        return strcmp((*p1)->name, (*p2)->name);
}

推荐阅读