结构数组的动态内存分配

Question

所以我一直在做我的一个小项目，但我被困在了这个阶段。我不断收到段错误，我越来越绝望。我有 2 个结构

typedef struct {
    float time;
}Race;

typedef struct {
    char DriverName[50];
    int NoRaces;
    Race *races;
}Driver;

我必须为单个车手分配内存，然后在获得每个车手的比赛次数后为一组车手分配内存。这是我目前的代码

Driver *allocDriver(int noRaces) {
    Driver *driver;
    driver = (Driver *)malloc(sizeof(Driver));
    driver->NoRaces = noRaces;
    driver->races = (Race *)malloc(sizeof(Race));       

    return driver;}


Driver **allocDrivers(int driversNo, int *driversRacesNo) {
    int i;
    Driver **drivers;
    drivers = (Driver **)malloc(driversNo * sizeof(Driver *));
    for(i = 0; i < driversNo; i++)
        drivers[i] = allocDriver(driversRacesNo[i]);

    return drivers;}

Answer 1

这是一个关于结构表分配的“扩展”但简单的示例，在 ubuntu 18.04 上编译。希望它能够自我解释和说明。对于未来的开发和练习，尝试使用链表而不是数组。

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

typedef struct sRace {
    float time;
}Race;

typedef struct sDriver {
    char DriverName[50];
    int NoRaces;
    Race *races;
}Driver;


typedef struct sDriversTable {
    int numdrivers;
    Driver** drivers;
} DriversTable;



Driver *allocDriver(char* name, int numraces)
{
    Driver *driver = calloc(1, sizeof(Driver));
    driver->NoRaces = numraces;
    strcpy(driver->DriverName, name);
    driver->races = calloc(numraces,sizeof(Race));
    return driver;
}

DriversTable* allocDriversTable(int numdrv)
{
     DriversTable* dt = calloc(1,sizeof(DriversTable));
     dt->numdrivers = numdrv;
     dt->drivers = calloc(dt->numdrivers, sizeof(Driver*));
    return dt;
}


void addDriver(DriversTable* drv, char* name, int numraces)
{
    for(int i = 0; i < drv->numdrivers; i++)
    {
        if( drv->drivers[i]  == NULL)
        {
            drv->drivers[i] = allocDriver(name, numraces);
            break;
        }
    }
}

void setDriverTimeForTheRace(DriversTable* drv, char* name, int raceindex, float time)
{

    for(int i = 0; i < drv->numdrivers; i++)
    {
        if( !strcmp(drv->drivers[i]->DriverName,name) )
        {
            if( raceindex < drv->drivers[i]->NoRaces )
            {
               drv->drivers[i]->races[raceindex].time = time;
            }
            else
            {
                printf("invalid race index. %d, (max. for the driver %s is %d\n",raceindex,drv->drivers[i]->DriverName, drv->drivers[i]->NoRaces -1);
            }
            break;
        }
    }
}

void printDriversTable(DriversTable* drv)
{
    for(int i = 0; i < drv->numdrivers; i++)
    {
        if( drv->drivers[i]  != NULL)
        {
            printf("Driver:%s, Races: %2d\n", drv->drivers[i]->DriverName, drv->drivers[i]->NoRaces);
            for(int j = 0; j < drv->drivers[i]->NoRaces; j++)
            {
                if(drv->drivers[i]->races[j].time > 0.0 )
                    printf("{%4.2f}", drv->drivers[i]->races[j].time);
                else
                    printf("{%4s}", "n/a");
            }
            printf("\n");
        }
    }
}

void ReleaseResources(DriversTable** dt)
{
    DriversTable* drv = *dt;
    if( drv == NULL)
    {
      printf("nothing to release!\n");
      return;
    }
    for(int i = 0; i < drv->numdrivers; i++)
    {
        if( drv->drivers[i]  != NULL)
        {
            free(drv->drivers[i]->races);
            drv->drivers[i]->races = NULL;
            free(drv->drivers[i]);
            drv->drivers[i]=NULL;
        }
    }

    free(drv->drivers);
    drv->drivers = NULL;
    free(drv);
    *dt = NULL;
    printf("released!\n");
}

int main()
{
    DriversTable *drv = allocDriversTable(10);
    addDriver(drv,"Emerson", 6);
    setDriverTimeForTheRace(drv,"Emerson",1, 34.5);
    setDriverTimeForTheRace(drv,"Emerson",2, 33.6);
    setDriverTimeForTheRace(drv,"Emerson",7, 34.5);
    addDriver(drv,"Lake",7);
    setDriverTimeForTheRace(drv,"Lake",3, 21.5);
    setDriverTimeForTheRace(drv,"Lake",5, 22.6);
    setDriverTimeForTheRace(drv,"Lake",7, 23.5);
    addDriver(drv,"Palmer",8);
    setDriverTimeForTheRace(drv,"Palmer",4, 21.5);
    setDriverTimeForTheRace(drv,"Palmer",6, 22.6);
    setDriverTimeForTheRace(drv,"Palmer",7, 23.5);
    printDriversTable(drv);
    ReleaseResources(&drv);
    ReleaseResources(&drv);
    return 0;
}

Answer 2

虽然我不确定，因为我不知道你如何从main 中调用这些，也不知道作业的内容；我怀疑您需要更改以下行；

driver->races = (Race *)malloc(sizeof(Race));

喜欢：

driver->races = (Race *)malloc(noRaces * sizeof(Race));

例如，您的代码存储 5 作为比赛次数，但没有为 struct Race 分配 5 个内存空间（我认为，此结构用于比赛结果）；目前，它只分配struct Race 的一个mem-width。