c - C 中返回结构表的函数

Question

我有一个结构体调用 Client ，以及一个创建此类结构体的函数 initClient 。

现在我想实现一个函数来创建此结构的table[20000]，但我无法弄清楚返回数据的正确语法。是 Client** 还是 Client[] ？...这是我的代码:client.h:

 struct sClient
 {
     int num_tel;
     int nbr_appel;
     int cout;
  };

  typedef struct sClient Client;
  Client * initClient(int num_tel, int nbr_appel,int cout);
  Client *createData();

和main.c:

#include <stdio.h>
#include <stdlib.h>
#include "client.h"

Client* initClient(int num_tel, int nbr_appel,int cout){
    Client *c = (Client *) malloc(sizeof(Client)); 
    c-> num_tel =num_tel;
    c-> nbr_appel= nbr_appel; 
    c-> cout= cout;

    return c; 
}

Client* createData(){
    // Number of clients
    #define NBCLIENT 20 
    Client* tab[NBCLIENT];
    Client *c; 
    int i,numeroTel,prixAppel;

    for(i=0;i<NBCLIENT;i++)
    {
        // Generation of a random num_tel
        numeroTel = 600000000+(rand() % NBCLIENT);   
        prixAppel = (rand() % 400)+1; 
        c=initClient(numeroTel,1,prixAppel);
        tab[i]=c;      
    }   
    return tab;    
}

int main(int argc, char *argv[])
{
    createData();
    system("PAUSE");    
    return 0;
}

Answer 1

根据评论中讨论的内容(并考虑到我给出了一些可能令人困惑的提示)，我想展示我看到的满足所有要求的(唯一)解决方案:

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

typedef struct { int num_tel, nbr_appel, cout; } Client;

Client* initClient(int num_tel, int nbr_appel, int cout);
Client* createData();

#define NBCLIENT 20

Client* initClient(int num_tel, int nbr_appel, int cout)
{
  Client *pClient = malloc(sizeof (Client));
  /** @bug check for NULL pointer missing! */
  pClient->num_tel = num_tel;
  pClient->nbr_appel = nbr_appel;
  pClient->cout = cout;
  return pClient;
}

Client* createData()
{
  Client *clients = malloc(NBCLIENT * sizeof (Client));
  /** @bug check for NULL pointer missing! */
  for (int i = 0; i < NBCLIENT; ++i) {
    int numeroTel = 600000000 + (rand() % NBCLIENT);
    int prixAppel = (rand() % 400) + 1;
    Client *pClient = initClient(numeroTel,1,prixAppel);
    /* copy returned CONTENTS to malloc-ed array element */
    clients[i] = *pClient; /* assignment for struct-s is granted */
    /* release pClient to prevent memory leaks - it's not anymore needed */
    free(pClient);
  }
  return clients;
}

int main()
{
  Client *clients = createData();
  for (int i = 0; i < NBCLIENT; ++i) {
    Client *pClient = clients + i; /* or: &clients[i] would work as well */
    printf("%2d.: %d, %d, %d\n",
      i, pClient->num_tel, pClient->nbr_appel, pClient->cout);
  }
  free(clients);
  return 0;
}

因此，为了匹配所需的签名，initClient() 返回的 struct 值被复制到数组 malloc()-ed 中createData()。通过这种方式，free() 对于防止内存泄漏非常重要，因为 initClient() 中完成的 malloc() 的内存是之后既没有使用也没有引用。

在 ideone 上编译并测试。输出为:

 0.: 600000003, 1, 87
 1.: 600000017, 1, 116
 2.: 600000013, 1, 336
 3.: 600000006, 1, 93
 4.: 600000009, 1, 222
 5.: 600000002, 1, 28
 6.: 600000010, 1, 60
 7.: 600000003, 1, 327
 8.: 600000000, 1, 227
 9.: 600000012, 1, 137
10.: 600000011, 1, 169
11.: 600000007, 1, 30
12.: 600000002, 1, 331
13.: 600000002, 1, 324
14.: 600000007, 1, 336
15.: 600000009, 1, 203
16.: 600000002, 1, 259
17.: 600000009, 1, 168
18.: 600000013, 1, 57
19.: 600000011, 1, 43

<小时/>

在 initClient() 中分配的临时内存和 createData() 中的 free-d 会令我烦恼。可以通过稍微更改 initClient() 的签名来防止这种情况:

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

typedef struct { int num_tel, nbr_appel, cout; } Client;

void initClient(Client *pClient, int num_tel, int nbr_appel, int cout);
Client* createData();

#define NBCLIENT 20

void initClient(Client *pClient, int num_tel, int nbr_appel, int cout)
{
  pClient->num_tel = num_tel;
  pClient->nbr_appel = nbr_appel;
  pClient->cout = cout;
}

Client* createData()
{
  Client *clients = malloc(NBCLIENT * sizeof (Client));
  /** @bug check for NULL pointer missing! */
  for (int i = 0; i < NBCLIENT; ++i) {
    int numeroTel = 600000000 + (rand() % NBCLIENT);
    int prixAppel = (rand() % 400) + 1;
    initClient(clients + i, numeroTel, 1, prixAppel); 
    /* &clients[i] would've worked as well as clients + i */
  }
  return clients;
}

int main()
{
  Client *clients = createData();
  for (int i = 0; i < NBCLIENT; ++i) {
    Client *pClient = clients + i; /* or: &clients[i] would work as well */
    printf("%2d.: %d, %d, %d\n",
      i, pClient->num_tel, pClient->nbr_appel, pClient->cout);
  }
  free(clients);
  return 0;
}

在 ideone 上再次编译并测试。输出为:

 0.: 600000003, 1, 87
 1.: 600000017, 1, 116
 2.: 600000013, 1, 336
 3.: 600000006, 1, 93
 4.: 600000009, 1, 222
 5.: 600000002, 1, 28
 6.: 600000010, 1, 60
 7.: 600000003, 1, 327
 8.: 600000000, 1, 227
 9.: 600000012, 1, 137
10.: 600000011, 1, 169
11.: 600000007, 1, 30
12.: 600000002, 1, 331
13.: 600000002, 1, 324
14.: 600000007, 1, 336
15.: 600000009, 1, 203
16.: 600000002, 1, 259
17.: 600000009, 1, 168
18.: 600000013, 1, 57
19.: 600000011, 1, 43