C在struct-free()中动态分配结构

Question

我有两个结构，"link_time"one_answers"vehicle_information"，我正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"包含一个指针，用于分配动态大小的"link_time"数组。我在其他堆栈文章中读到，如果我将指针声明为结构的最后一个成员，那么我可以像控制动态内存块一样控制这个成员（malloc、realloc、free）。我也知道我需要一个免费的每个malloc，我相信我做得对。

我对"vehicle_info"结构进行malloc，然后在"vehicle _info"中对"link_time"结构进行"ltt"。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会抱怨，并且我的程序崩溃：

    //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"阵列中。下面的伪代码：

    ...
    //***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，我会尽可能对称，我将不胜感激。

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，但随后您丢失了TEMP_VEHICLE_INFO[k] = target_array[k]代码行覆盖的内存。

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()，使服务代码远离主控制流，使代码更加清晰可读。这将对你避免此类问题有很大帮助。

或者更好——使用C++，忘记这个手动内存控制地狱。