我使用链表用 C 编写了一个简单堆栈的小实现。该应用程序在对 gdb 和 valgrind 进行了一番折腾后工作。但是，我注意到 valgrind 在程序终止时报告了一些“仍然可以访问”的泄漏。
经过一些谷歌搜索后，我发现这些类型的泄漏不是问题，我通常不应该担心它们。嗯，这是个好消息!唯一的问题是，我真的很想了解为什么 valgrind 会看到这些泄漏以及它们出现的位置。在这个应用程序的第一遍中，我煞费苦心地释放所有分配的内存。我错过了什么？ valgrind 看到但我看不到的这些分配在哪里？
我已经盯着这个看了一段时间了，尽管以这种方式摆弄代码，但还是空手而归。希望大家能在这方面帮助我。
我已将应用程序简化为一个最小的示例，该示例将显示我观察到的泄漏。它只是初始化堆栈，然后立即销毁它并退出。
// simple stack implementation
#include <stdio.h>
#include <assert.h>
#include <string.h>
#include <stdlib.h>
/*--- data structure in a stack item ---*/
struct data {
char * message;
};
/*--- stack item structure ---*/
struct item {
struct data * my_data;
struct item * next;
};
/*--- stack data structure ---*/
struct stack {
int initialized;
int empty;
struct item * head;
};
struct stack * my_stack;
/*--- create a new stack data structure with provided initial data ---*/
int
create_stack(struct data ** initial_items, int num_items) {
//allocate memory for the stack structure itself
my_stack = (struct stack *) malloc(sizeof(struct stack));
if(!my_stack) return -1;
my_stack->empty = 1;
my_stack ->initialized = 0;
if(num_items) {
//allocate memory for the head of the list first
my_stack->head = (struct item *) malloc(sizeof(struct item));
if(!my_stack->head) return -1;
my_stack->head->my_data = initial_items[0];
my_stack->head->next = NULL;
struct item * tracker = my_stack->head;
//fill the stack with elements containing the provided data
int i = 1;
for(; i < (num_items); i++) {
tracker->next = (struct item *) malloc(sizeof(struct item));
tracker = tracker->next;
if(!tracker) return -1;
tracker->my_data = initial_items[i];
tracker->next = NULL;
}
//no longer empty
my_stack->empty = 0;
}
//set initialized flag & return
my_stack->initialized = 1;
return 0;
}
/*--- destroy the stack by recursively freeing nodes ---*/
int
destroy_stack(struct item * recurse) {
//if the starting node is valid, begin
if(recurse) {
//if the current node links to another
if(recurse->next)
//recurse on the next node
destroy_stack(recurse->next);
else
//otherwise we hit the end, free the node
free(recurse);
}
//the starting node is invalid, just free the stack itself
else {
free(my_stack);
}
return 0;
}
/*--- test wrapper ---*/
int
main(int argc, char **argv) {
//initialize 10 element list of data structures to fill the stack items with
int i = 0;
int length = 10;
struct data ** initial_values = (struct data **) malloc(length*sizeof(struct data *));
//set each data element's value to i
for(; i < length; i++) {
char temp[16];
sprintf(temp, "%d", i);
initial_values[i] = (struct data *) malloc(sizeof(struct data));
initial_values[i]->message = strdup(temp);
}
//simple test case
//create a stack with the generated initial data, then destroy it
assert( !create_stack(initial_values, length) );
assert( !destroy_stack(my_stack->head) );
//free the string data our stack nodes were pointing to
i = 0;
while(i < length) {
free(initial_values[i]->message);
free(initial_values[i]);
i += 1;
}
free(initial_values);
return 0;
}
通过 valgrind 运行它会产生以下已识别的未发布 block :
(trusty)kin3tix@localhost:~/C Practice/Data Structures$ valgrind --leak-check=full --show-leak-kinds=all ./stack_leak_test
==19340== Memcheck, a memory error detector
==19340== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==19340== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info
==19340== Command: ./stack_leak_test
==19340==
==19340==
==19340== HEAP SUMMARY:
==19340== in use at exit: 168 bytes in 10 blocks
==19340== total heap usage: 32 allocs, 22 frees, 364 bytes allocated
==19340==
==19340== 16 bytes in 1 blocks are still reachable in loss record 1 of 3
==19340== at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==19340== by 0x400739: create_stack (stack_leak_test.c:40)
==19340== by 0x40093B: main (stack_leak_test.c:95)
==19340==
==19340== 24 bytes in 1 blocks are still reachable in loss record 2 of 3
==19340== at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==19340== by 0x4006E6: create_stack (stack_leak_test.c:33)
==19340== by 0x40093B: main (stack_leak_test.c:95)
==19340==
==19340== 128 bytes in 8 blocks are still reachable in loss record 3 of 3
==19340== at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==19340== by 0x4007A1: create_stack (stack_leak_test.c:48)
==19340== by 0x40093B: main (stack_leak_test.c:95)
==19340==
==19340== LEAK SUMMARY:
==19340== definitely lost: 0 bytes in 0 blocks
==19340== indirectly lost: 0 bytes in 0 blocks
==19340== possibly lost: 0 bytes in 0 blocks
==19340== still reachable: 168 bytes in 10 blocks
==19340== suppressed: 0 bytes in 0 blocks
==19340==
==19340== For counts of detected and suppressed errors, rerun with: -v
==19340== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
它们似乎都源于“create_stack”，但据我所知，我的销毁函数应该捕获我分配的所有内容。我在这里缺少什么？
最佳答案
您的销毁逻辑试图在一个函数中递归地合并两个任务(删除堆栈对象及其项)。更糟糕的是，else 状态根本不应该存在。。您已经确定您正坐在一个动态节点上 (recurse)。它需要被删除。它是否有next 不是由当前深度决定的；这将在下一个递归深度中得到处理。
老实说，如果你创建一个助手来清除链表，并作为单独的包装器对堆栈本身做同样的事情，这会简单得多:
/*--- destroy linked list nodes recursively ---*/
static void destroy_stack_items(struct item *item)
{
if (item)
{
destroy_stack_items(item->next);
free(item);
}
}
/*--- destroy the stack by recursively freeing nodes ---*/
int destroy_stack(struct stack *s)
{
if (s)
{
destroy_stack_items(s->head);
free(s);
}
return 0
}
并简单地调用为:
destroy_stack(my_stack);
就我个人而言，我会反复执行此操作(因此在此过程中删除助手)，但我相信您有其他原因。例如:
/*--- destroy the stack by iteratively freeing nodes ---*/
int destroy_stack(struct stack *s)
{
if (s)
{
while (s->head)
{
struct item *tmp = s->head;
s->head = tmp->next;
free(tmp);
}
free(s);
}
return 0
}
祝你好运。
关于c - Valgrind 检测到可到达的泄漏，它们在哪里？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/31738264/