Question

I have a bit of a problem. I am barely starting out with C, (comming from a C# background) and I am having problem with double pointers.

I have a structure as follows:

#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

Implementation:

#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);
    }
}

so now I have to manage a whole lot of ProcessInfo instances. I wrote another structure which would hold a pointer to a pointer to the ProcessInfo sturcture because i thought that I can increase and decrease it in size as needed (without too much hassle);

#ifndef __SCHEDULER_H
#define __SCHEDULER_H

struct Scheduler
{
    struct ProcessInfo** Processes;
};

struct Scheduler* Scheduler_Allocate(void);

#endif

So the question is how do I initialize the **Processes member inside the Scheduler_Allocate method? How do I add stuff to it?

Answer 1

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++;

Also see my example here:

Array of C structs