在不同的功能分配的内存？ [英] Free memory allocated in a different function?

问题描述

我想学习C和我目前正在写一个基本的堆栈数据结构，但我似乎无法得到基本的malloc / 免费的权利。

I'm trying to learn C and I'm currently trying to write a basic stack data structure, but I can't seem to get basic malloc/free right.

这里的code我一直在使用（我只是张贴的一小部分在这里说明一个具体的问题，而不是总code，但通过运行这个例子只是$产生的错误信息C $℃的的valgrind ）

Here's the code I've been using (I'm just posting a small part here to illustrate a specific problem, not the total code, but the error message was generated just by running this example code in valgrind)

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

typedef struct Entry {
    struct Entry *previous;
    int value;
} Entry;

void destroyEntry(Entry entry);

int main(int argc, char *argv[])
{
    Entry* apple;
    apple = malloc(sizeof(Entry));
    destroyEntry(*(apple));
    return 0;
}

void destroyEntry(Entry entry)
{
    Entry *entry_ptr = &entry;
    free(entry_ptr);
    return;
}

当我与运行它通过的valgrind - 泄漏检查=全--track-起源= YES ，我得到以下错误：

When I run it through valgrind with --leak-check=full --track-origins=yes, I get the following error:

==20674== Invalid free() / delete / delete[] / realloc()
==20674==    at 0x4028E58: free (vg_replace_malloc.c:427)
==20674==    by 0x80485B2: destroyEntry (testing.c:53)
==20674==    by 0x8048477: main (testing.c:26)
==20674==  Address 0xbecc0070 is on thread 1's stack

我觉得这个错误意味着 destroyEntry 功能是不允许修改主要明确分配的内存。是对的吗？为什么我不能只是免费我在主在另一个函数分配的内存？ （并且这种行为在某种程度上具体到主？）

I think this error means that the destroyEntry function is not allowed to modify memory allocated explicitly in main. Is that right? Why can't I just free the memory I allocated in main in another function? (and is this behavior somehow specific to main?)

推荐答案

当你传递参数给一个函数，它复制了一份，而且功能适用于该副本。所以你的情况，你想免费原来的对象，这没有任何意义的副本。

Whenever you pass a parameter to a function, a copy is made, and the function works on that copy. So in your case, you are trying to free a copy of the original object, which doesn't make any sense.

您应该修改你的函数取一个指针，然后你可以把它称之为免费直接在该指针。

You should modify your function to take a pointer, and then you can have it call free directly on that pointer.

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