c - 无法初始化结构数组

Question

我正在尝试使用 memset 初始化 struct 类型的数组单元。该程序成功编译，但是 Valgrind 对与 memseting 这些单元格相关的事情不满意。注释掉的代码也不起作用。

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

#define MAX_DATA 512
#define MAX_ROWS 100



struct Address {
        int id;
        int set;
        char name[MAX_DATA];
        char email[MAX_DATA];
};

struct Database{
        struct Address rows[MAX_ROWS];
};

struct Connection{
        FILE* file;
        struct Database* db;
};


void die(const char* message)
{
        if(errno){
                perror(message);
        }else{
                printf("ERROR: %s\n", message);
        }
        exit(1);
}



void Database_load(struct Connection* conn)
{
        int rc = fread(conn->db, sizeof(struct Database), 1, conn->file);
        if (rc != 1)
        {
                die("Failed to load database.");
        }
}


struct Connection* Database_open(const char* filename, char mode)
 {
        struct Connection* conn = malloc(sizeof(struct Connection));
        if (!conn)
        {
                die("Memory error");
        }

        if (mode == 'c')
        {
                conn->file = fopen(filename, "w");
        }
        else
        {
                conn->file = fopen(filename, "r+");

                if(conn->file) {
                        Database_load(conn);
                }
        }

        if(!conn->file) die("Failed to open file");
        return conn;
}


void Database_create(struct Connection* conn)
{
        int i = 0;

        for(i = 0; i < MAX_ROWS; i++) {
                //struct Address addr = {.id = i, .set = 0};
                //conn->db->rows[i] = addr;
                memset(&(conn->db->rows[i]), 0, sizeof(struct Address));
                conn->db->rows[i].id = i;
        }
}




int main(int argc, char* argv[])
{
        if(argc < 3) die("USAGE: ex17 <dbfile> <action> [action params]");

        char* filename = argv[1];
        char action = argv[2][0];
        struct Connection* conn = Database_open(filename, action);
        int id = 0;
        if(argc > 3) id = atoi(argv[3]);
        if(id >= MAX_ROWS) die("There's not that many records.");


        Database_create(conn);

        return 0;
}                        

相关的 Valgrind 错误 -

==16227== Conditional jump or move depends on uninitialised value(s)
==16227==    at 0x4C3009C: memset (vg_replace_strmem.c:1224)
==16227==    by 0x400BA8: Database_create (ex17.c:108)
==16227==    by 0x400EE1: main (ex17.c:174)

Answer 1

您的代码永远不会初始化conn->db

你需要这样的东西:

conn->db = malloc(sizeof(struct Database));
if (!conn->db) 
{
    die("Memory error");
}

在Database_open函数内部