C 在 struct free() 中动态分配结构

Question

我有两个结构，“link_time”和“vehicle_information”，我在交通模拟插件中使用它们。我很难为我创建的两个自定义结构正确释放(和分配？)内存。

//global vardeclarations
//GLOBAL_VEHICLE_INFO contains all of the "vehicle_information" structs             
//representing all of the vehicles within the simulation
vehicle_information_template* GLOBAL_VEHICLE_INFO;
int lengthGLOBALVEHICLE;

vehicle_information_template* TEMP_VEHICLE_INFO;

//struct definitions
typedef struct link_time{

     float link_duration;
     float timestamp;

}link_time_template;

 typedef struct vehicle_information{
     int id;
     int current_link_id;
     float start_time;
     link_time_template* ltt; //individual vehicle link travel times array

}vehicle_information_template;


//function to add new "vehicle_information_template" to GLOBAL_VEHICLE_ARRAY
vehicle_information_template* addToGlobalVehicleArray(vehicle_information_template* target_array, int array_length, vehicle_information_template new_vinfo){
    int k;

    //allocate space for temp holding array, both the 'vehicle_information' struct and the 'link_time' struct within 'vehicle_information' struct

    TEMP_VEHICLE_INFO = malloc( sizeof(vehicle_information_template) * (array_length+1) );
    for(k=0;k<array_length+1;k++){
        TEMP_VEHICLE_INFO[k].ltt = malloc( sizeof(link_time_template) * NUM_LINKS);
    }


    //copy contents so that target_array can be free'd and resized
    for(k=0;k<array_length;k++){
        TEMP_VEHICLE_INFO[k] = target_array[k];
    }

    //add the new vehicle_info to the end of the TEMP_VEHICLE_INFO(newly resized)
    TEMP_VEHICLE_INFO[array_length] = new_vinfo;

       //****BREAKS HERE *****
    //free target_array (GLOBAL_VEHICLE_ARRAY) so that it can be resized to one element larger
//free the struct in the reverse order, freeing 'ltt' first, as it is a member of the larger struct 'vehicle_info'
    for(k=0;k<array_length;k++){
        free(target_array[k].ltt);
    }
    free(target_array);

    //reallocate GLOBAL_VEHICLE to 1 size larger to accomodate new element
    target_array = malloc(sizeof(vehicle_information_template) * (array_length+1) );
    //allocate space for "link_time" struct within "vehicle_information" struct
    for(k=0;k<array_length+1;k++){
        target_array[k].ltt = malloc(sizeof(link_time_template) * NUM_LINKS);
    }
    //copy contents from temp array to global array
    for(k=0;k<(array_length+1);k++){
        target_array[k] = TEMP_VEHICLE_INFO[k];
    }
    //free temp array struct
    for(k=0;k<array_length;k++){
        free(TEMP_VEHICLE_INFO[k].ltt);
    }
    free(TEMP_VEHICLE_INFO);
    //return newly sized global array
    return target_array;

}

“vehicle_information”包含一个用于分配动态大小的“link_time”数组的指针。我在其他堆栈帖子中读到，如果我将指针声明为结构的最后一个成员，那么我可以控制该成员，就好像它是一 block 动态内存(malloc、realloc、free)一样。我还知道我需要为每个 malloc 分配一个 free，我相信我做得正确。

我为“vehicle_info”结构分配内存，然后为“vehicle_info”内的“link_time”结构“ltt”分配内存。我假设我以相反的顺序释放，因为“ltt”在内存中链接到“vehicle_info？”但是当我到达函数“vehicle_information_template* addToGlobalVehicleArray()”中的以下行时，HEAP 提示并且我的程序崩溃了:

    //free target_array (GLOBAL_VEHICLE_ARRAY) so that it can be resized to one element larger
//free the struct in the reverse order, freeing 'ltt' first, as it is a member of the larger struct 'vehicle_info'
    for(k=0;k<array_length;k++){
        free(target_array[k].ltt);
    }

    free(target_array);

每次车辆进入模拟时，都应将其添加到“GLOBAL_VEHICLE_INFO”数组中。伪代码如下:

    ...
    //***vehicle enters network

    vehicle_information_template temp_v;
    int k;
    //set temp_v to the newly released vehicle's information so it can be added to GLOBAL_VEHICLE_INFO
    temp_v.id = qpg_VHC_uniqueID(v);
    temp_v.current_link_id = qpg_LNK_index(qpg_VHC_link(v));
    temp_v.start_time = -1.0;

    //allocate memory for temp_v.ltt
    temp_v.ltt = malloc(sizeof(link_time_template) * NUM_LINKS);
    //set link_duration and timestamp to dummy values
    for(k=1;k<=NUM_LINKS;k++){
        temp_v.ltt[k].link_duration = -1.0;
        temp_v.ltt[k].timestamp = -1.0;
    }

 //add temp_v to "GLOBAL_VEHICLE_INFO" using function
    GLOBAL_VEHICLE_INFO = addToGlobalVehicleArray( GLOBAL_VEHICLE_INFO, lengthGLOBALVEHICLE, temp_v);
    lengthGLOBALVEHICLE++;

    //free allocated temp_v.ltt (link_travel_time)
    free(temp_v.ltt);

如果有人对我如何处理指针或内存有任何解决方案或建议，我会尽力保持对称，我将非常感激。

Answer 1

我在 addToGlobalVehicleArray 函数的第一行中看到了问题 - 您分配了 TEMP_VEHICLE_INFO[k].ltt 内存，但随后您通过 TEMP_VEHICLE_INFO[ 覆盖了它k] = target_array[k] 代码行。

还建议让您的代码更加结构化 - 引入单独的函数create_link_time_array()/free_link_time_array()、create_veh_info_array()/free_veh_info_array() 将服务代码移离主控制流，使代码更加清晰易读。这将极大地帮助您避免此类问题。

或者更好 - 使用 C++ 并忘记这个手动内存控制 hell 。