ReAlloc如果不调整指针数组 [英] Realloc is not resizing array of pointers

问题描述

我一直传递和返回dirs_later_array。当我到了new_size = ...中的其他块，我结束了2 new_size第二次左右。到现在为止还挺好。但是，当我做的realloc

  dirs_later_array = realloc的（dirs_later_array，
new_size *的sizeof（结构dirs_later *））;
 

的 sizeof的保持在图4中，指针的大小，为dirs_later_array。我能够在dirs_later_array [1]，以成功地存储，但该值不断被覆盖掉，下一次我进入的功能。

结构dirs_later ** add_struct（为const char * findme，结构的dirent * DPTR，
        结构统计* this_lstat，字符* RELATIVE_PATH，为const char * type_str，
        结构dirs_later ** dirs_later_array）{    结构dirs_later * NEW_DIR =的malloc（sizeof的（结构dirs_later））;
    check_realloc_dirs_error（NEW_DIR）;    如果（STRCMP（dptr-> d_name，。））{//目录，而不是同一个目录
        //相对路径复制到结构
        字符* relative_path2;
        relative_path2 = malloc的（strlen的（RELATIVE_PATH）+1）;
        check_realloc_error（relative_path2）;
        的strcpy（relative_path2，RELATIVE_PATH）;        //如果（strlen的（RELATIVE_PATH）> 0）
        // relative_path2 [strlen的（RELATIVE_PATH） -  1] ='\\ 0';        如果（NULL！= NEW_DIR）{
            new_dir-> findme = findme;
            new_dir-> DPTR = DPTR;
            new_dir-> ST_MODE = this_lstat-> ST_MODE;
            new_dir-> RELATIVE_PATH = relative_path2;
            new_dir-> type_str = type_str;
        }
        INT new_size = 0;
        / *
         //检查，如果这是在结构中的第一个元素
         如果（sizeof的（dirs_later_array）/的sizeof（结构dirs_later *）== 1）{
         new_size = 1;
         }
         * /
        如果（dirs_later_array == NULL）{
            dirs_later_array =的malloc（sizeof的（结构dirs_later *））; //存储目录结构或过程的后期
            check_realloc_arr_error（* dirs_later_array）;
            new_size = 1;
        }其他{            //将目录添加到目录阵列
            new_size =（（（的sizeof（dirs_later_array）+的sizeof（结构dirs_later *）））/的sizeof（结构dirs_later *））;
            //输出（新大小：％D，new_size）;
        }
        dirs_later_array =的realloc（dirs_later_array，
                new_size *的sizeof（结构dirs_later *））;
        check_realloc_arr_error（dirs_later_array）;
        dirs_later_array [new_size  -  1] = NEW_DIR;
    }
    返回dirs_later_array;
}

解决方案

运营商的sizeof 是一个编译时功能，它只检查一个前$ P $的静态大小pssion。因此，对于指针它只返回指针是4平台上的大小。 的sizeof 并不衡量一个动态分配的数据的大小。在C中没有标准的功​​能来获取动态分配数据的大小。

I keep passing in and returning the dirs_later_array. When I get to "new_size=..." in the else block, I end up with new_size of 2 the second time around. So far so good. But when I do a realloc

dirs_later_array = realloc(dirs_later_array,
new_size * sizeof(struct dirs_later*));

the sizeof remains at 4, the size of the pointer, for dirs_later_array. I'm able to succesfully store at dirs_later_array[1] but that value keeps getting overwritten the next time I go into the function.

struct dirs_later** add_struct(const char *findme, struct dirent *dptr,
        struct stat *this_lstat, char *relative_path, const char *type_str,
        struct dirs_later **dirs_later_array) {

    struct dirs_later *new_dir = malloc(sizeof(struct dirs_later));
    check_realloc_dirs_error(new_dir);

    if (strcmp(dptr->d_name, ".")) { //Dir and not same directory
        //Copy the relative path to the struct
        char *relative_path2;
        relative_path2 = malloc(strlen(relative_path) + 1);
        check_realloc_error(relative_path2);
        strcpy(relative_path2, relative_path);

        //if (strlen(relative_path) > 0)
        //    relative_path2[strlen(relative_path) - 1] = '\0';

        if (NULL != new_dir) {
            new_dir->findme = findme;
            new_dir->dptr = dptr;
            new_dir->st_mode = this_lstat->st_mode;
            new_dir->relative_path = relative_path2;
            new_dir->type_str = type_str;
        }
        int new_size = 0;
        /*
         //Check if this is the first element in the struct
         if (sizeof(dirs_later_array) / sizeof(struct dirs_later*) == 1) {
         new_size = 1;
         }
         */
        if (dirs_later_array == NULL) {
            dirs_later_array = malloc(sizeof(struct dirs_later*)); //Store the directory structures or process later
            check_realloc_arr_error(*dirs_later_array);
            new_size = 1;
        } else {

            //Add directories to directories array
            new_size = (((sizeof(dirs_later_array) + sizeof(struct dirs_later*)))/sizeof(struct dirs_later*));
            //printf("new size: %d",new_size);
        }
        dirs_later_array = realloc(dirs_later_array,
                new_size * sizeof(struct dirs_later*));
        check_realloc_arr_error(dirs_later_array);
        dirs_later_array[new_size - 1] = new_dir;
    }
    return dirs_later_array;
}

解决方案

Operator sizeof is a compile time feature and it only checks the static size of an expression. So for pointer it only returns the size of that pointer which is 4 on your platform. sizeof does not measure the size of a dynamically allocated data. There is no standard feature in C to get the size of dynamically allocated data.

这篇关于ReAlloc如果不调整指针数组的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！