内存泄漏Valgrind

Question

我写了一个程序,用五个字符串串起一个字符串.这是我的计划.

struct list
{
    char *str;
    struct list* next;
};

struct list* head = NULL;

void insert(char *cont)
{
    struct list* temp = (struct list*)malloc(sizeof(struct list));

    size_t len = strlen(cont);
    char *heapString = (char*)malloc(len);
    strcpy(heapString,cont);

    temp->str = heapString;
    temp->next = NULL;

    if(head == NULL)
    {
        head = temp;
        return ;
    }

    temp->next = head;
    head = temp;
}
void print()
{
    struct list* temp = head;
    while(temp != NULL)
    {
        printf("%s\n",temp->str);
        temp = temp->next;
    }
}
void clearmem()
{
    struct list* temp = head;
    while(temp != NULL)
    {
        free(temp->str);
        free(temp);
        temp = temp->next;
    }
}
int main()
{
    char text[] = "abcdefghijklmno";
    size_t len = strlen(text);
    while(len !=0)
    {
        char *temp;
        temp = text ;
        temp = temp + len - 5;

        insert(temp);
        *(text+len-5) = '\0';
        len = strlen(text);
        free(temp);
    }
    print();
    clearmem();
}

我的程序工作正常.但是当我尝试通过Valgrind运行这个程序时,我得到了以下消息.它说有12个错误.

==2055== Invalid write of size 1
==2055==    at 0x4C32E0D: strcpy (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==2055==    by 0x10888C: insert (in /home/infant/Documents/Sample_codes/a.out)
==2055==    by 0x1089BD: main (in /home/infant/Documents/Sample_codes/a.out)
==2055==  Address 0x522d095 is 0 bytes after a block of size 5 alloc'd
==2055==    at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==2055==    by 0x108875: insert (in /home/infant/Documents/Sample_codes/a.out)
==2055==    by 0x1089BD: main (in /home/infant/Documents/Sample_codes/a.out)
==2055== 
==2055== Invalid free() / delete / delete[] / realloc()
==2055==    at 0x4C30D3B: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==2055==    by 0x1089EB: main (in /home/infant/Documents/Sample_codes/a.out)
==2055==  Address 0x1fff00030a is on thread 1's stack
==2055==  in frame #1, created by main (???:)
==2055== 
==2055== Invalid read of size 1
==2055==    at 0x4C32D44: __strlen_sse2 (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==2055==    by 0x4EBC9D1: puts (ioputs.c:35)
==2055==    by 0x1088FC: print (in /home/infant/Documents/Sample_codes/a.out)
==2055==    by 0x1089FC: main (in /home/infant/Documents/Sample_codes/a.out)
==2055==  Address 0x522d1d5 is 0 bytes after a block of size 5 alloc'd
==2055==    at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==2055==    by 0x108875: insert (in /home/infant/Documents/Sample_codes/a.out)
==2055==    by 0x1089BD: main (in /home/infant/Documents/Sample_codes/a.out)
==2055== 
abcde
fghij
klmno
==2055== Invalid read of size 8
==2055==    at 0x108947: clearmem (in /home/infant/Documents/Sample_codes/a.out)
==2055==    by 0x108A06: main (in /home/infant/Documents/Sample_codes/a.out)
==2055==  Address 0x522d188 is 8 bytes inside a block of size 16 free'd
==2055==    at 0x4C30D3B: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==2055==    by 0x108942: clearmem (in /home/infant/Documents/Sample_codes/a.out)
==2055==    by 0x108A06: main (in /home/infant/Documents/Sample_codes/a.out)
==2055==  Block was alloc'd at
==2055==    at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==2055==    by 0x108855: insert (in /home/infant/Documents/Sample_codes/a.out)
==2055==    by 0x1089BD: main (in /home/infant/Documents/Sample_codes/a.out)
==2055== 
==2055== 
==2055== HEAP SUMMARY:
==2055==     in use at exit: 0 bytes in 0 blocks
==2055==   total heap usage: 7 allocs, 10 frees, 1,087 bytes allocated
==2055== 
==2055== All heap blocks were freed -- no leaks are possible
==2055== 
==2055== For counts of detected and suppressed errors, rerun with: -v
==2055== ERROR SUMMARY: 12 errors from 4 contexts (suppressed: 0 from 0)

即使我清除了堆中的所有内存,我从4个上下文中得到12个错误.我的错误是什么？

Answer 1

一步步.

Invalid write of size 1

您malloc()没有为字符串终止符分配空间,但strcpy()尝试编写它.使用

char *heapString = malloc(len + 1);

代替.(注:不需投 void*来char*!).为简单起见,您也可以尝试使用(非标准)strdup(cont).

Invalid free() / delete / delete[] / realloc()

你temp指向一个char在text.使用没有任何意义free(),因为那里没有任何分配.删除该电话.

Invalid read of size 1

这应该与第一个错误有关.有趣的是print(),在编译时如何printf("%s\n",temp->str)将其转换为(更快)puts(temp->str).这就是Valgrind抱怨打电话的原因puts.

Invalid read of size 8

在

free(temp);
temp = temp->next;

你temp在被释放后阅读.