合并内存并处理 C 中的指针运算

Question

在下面的代码中，不知道为什么从来不输入if。对我来说，它在 if 中是有意义的:

void Mem_Coalesce(){


    list_t* temp;
    temp = freep;
        if(free_node_count == 2){
        //will finish
             printf("Addr of temp is  %llx\n\n", (long long unsigned) temp);
                 printf("Size of Temp is  %d\n\n", temp->size);
             printf("Addr of end of temp free node space is  %llx\n\n", (long long unsigned) ((char*)temp + temp->size));
             printf("Addr of start temp->next  is  %llx\n\n", (long long unsigned) temp->next);
        if( ((char*)temp + (temp->size)) == (char*)(temp->next)){
                printf("Entered the if statement\n");
                        temp->size += (temp->next)->size;
                temp->next = NULL;
        }


    }else {

        while(temp->next != NULL  ){

            if( ((char*)temp + (temp->size)) == (char*)(temp->next)){

                temp->size += (temp->next)->size;
                                printf("coalesced size is %d temp->size \n", temp->size);
                temp->next = (temp->next)->next;
                ((temp->next)->next)->prev = temp;
            }
            temp=temp->next;

        }

    }



}

结果是

Addr of temp is  7f9c1e89b070

Size of Temp is  200

Addr of end of temp free node space is  7f9c1e89b138

Addr of start temp->next  is  7f9c1e89b278

如您所见，它永远不会进入 if 语句。另外让我知道是否有任何其他更有效的内存合并算法。

Answer 1

您在这里以十进制打印 temp->size:

printf("Size of Temp is  %d\n\n", temp->size);
                         ^^

当您以十六进制打印出指针值时:

printf("Addr of temp is  %llx\n\n", (long long unsigned) temp);
                         ^^^^ 

200 十进制是 C8 的十六进制和 0xC8 + 0x70 = 0x138 .因此，当您将 0xC8 添加到 0x7f9c1e89b070 时，结果是 0x7f9c1e89b138 不等于 0x7f9c1e89b278 因此您不会输入if 语句。