Question

我有点问题。我几乎没有从C开始，（来自C＃背景）我遇到双指针问题。

我的结构如下：

#ifndef __PROCESSINFO_H
#define __PROCESSINFO_H

struct ProcessInfo
{
   int ProcesId;
   int Priority;
   int ExecutionTime;
   int EllapsedTime;
   char* ProcessName;
}; 

struct ProcessInfo *ProcessInfo_Allocate(int processId, char *processName, int priority, int executionTime);
void ProcessInfo_ToString(struct ProcessInfo *processInfo);
void ProcessInfo_Dispose(struct ProcessInfo *processInfo);

#endif

实施

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include "processinfo.h"

struct ProcessInfo *ProcessInfo_Allocate(int processId, char *processName, int priority, int executionTime)
{
    struct ProcessInfo *processInfo;
    processInfo = (struct ProcessInfo *)malloc(sizeof(struct ProcessInfo));
    processInfo->ProcessId = processId;
    processInfo->ProcessName = processName;
    processInfo->Priority = priority;
    processInfo->ExecutionTime = executionTime;
    processInfo->EllapsedTime = 0;

    return processInfo;
}

void ProcessInfo_ToString(struct ProcessInfo *processInfo)
{
    printf(" %6i %6i %10i %10i, %25s", processInfo->ProcessId, processInfo->Priority, processInfo->ExecutionTime, processInfo->EllapsedTime, processInfo->ProcessName); 
}

void ProcessInfo_Dispose(struct ProcessInfo *processInfo)
{
    if(processInfo != NULL)
    {
        if(processInfo->ProcessName != NULL)
        {
            free(processInfo->ProcessName);
        }

        free(processInfo);
    }
}

所以现在我必须管理大量的ProcessInfo实例。我写了另一个结构，它将指向指向ProcessInfo结构的指针，因为我认为我可以根据需要增加和减少它的大小（没有太多的麻烦）;

#ifndef __SCHEDULER_H
#define __SCHEDULER_H

struct Scheduler
{
    struct ProcessInfo** Processes;
};

struct Scheduler* Scheduler_Allocate(void);

#endif

所以问题是如何在Scheduler_Allocate方法中初始化** Processes成员？如何添加内容？

Answer 1

您不需要双指针来增加/减小大小。只需使用普通指针和realloc。

struct ProcessInfo* processes = malloc(sizeof(struct ProcessInfo) * 2);
struct ProcessInfo* processes_tmp;

if (!processes) {
   /* bail */
}

/* do whatever with processes[0] and [1] */

processes_tmp = processes;
processes = realloc(processes, sizeof(struct ProcessInfo) * 5);
if (!processes) {
    free(processes_tmp);
    /* bail */
}

/* processes[0] and [1] are unchanged, and [2] [3] and [4] are now valid */

然后你可以创建一个ProcessInfo_Allocate而不是ProcessInfo_Init，除了不分配内存之外，它会做大部分相同的事情：

int ProcessInfo_Init(struct ProcessInfo *pi, int processId, char *processName, int priority, int executionTime)
{
    if (!pi) {
        return -1;
    }
    pi->ProcessId = processId;
    pi->ProcessName = processName;
    pi->Priority = priority;
    pi->ExecutionTime = executionTime;
    pi->EllapsedTime = 0;

    return 0;
}

Answer 2

struct Scheduler s;
s.Processes = malloc(sizeof(struct ProcessInfo*) * size);
s.Processes[0] = ProcessInfo_Allocate(...);

// Add more items:
s.Processes = realloc(malloc(sizeof(struct ProcessInfo*) * (size + 1));
s.Processes[size] = ProcessInfo_Allocate(...);
size++;

另见我的例子：

Array of C structs

Answer 3

size_t size = 10;//or what ever is the number of processes
struct ProcessInfo * process = (struct ProcessInfo *)malloc(size * sizeof(struct ProcessInfo));
if(!process)
    //perhaps stop program? Do something
Processes = &process;
//later on
int i;
for(i = 0; i < size; i++)
{
   printf("Process id =%d",Processes[i]->ProcesId);
   etc
}

Answer 4

指针指针初始化为指针数组。所以请致电malloc(count * sizeof(ProcessInfo*))进行初始化。这样您就可以获得ProcessInfo的指针数组。然后多次调用malloc(sizeof(ProcessInfo))来创建特定的ProcessInfo结构，并将它们指向数组。

另外，user470379是正确的，您不需要指向指针的指针只是为了更改数组中的项目数。但是你的想法实际上也不错，如果你愿意的话，你可以坚持下去。

另外，由于您熟悉C＃，我建议您先从C中编写类似ArrayList的内容开始。然后您可以在很多情况下使用它（比如这个）。

Answer 5

首先将您的定义更改为：

typedef struct Scheduler {
    struct ProcessInfo** Processes;
} Scheduler;

然后是这样的：

Scheduler *s;
s = malloc(sizeof(Scheduler));
if (s == NULL) {
  exit(-1);
}
s = memset(s, 0, sizeof(Scheduler));
/* Or enter your own memory allocation stuff here */
i = 0; /* Or use some other number */
s->Processes[i] = someProcessInfo;

如何使用指向结构的指针？

5 个答案: