释放用malloc / Valgrind错误分配的内存

Question

我只是在学习C并且不明白为什么这一小段代码会导致内存泄漏：

mem_ptr=(char*)malloc(24);

if (mem_ptr == NULL){
    exit(EXIT_FAILURE);
}

mem_ptr="TEST";
printf("%s\n",mem_ptr);

free(mem_ptr);

当我跑步时，Valgrind告诉我：

==17900== Invalid free() / delete / delete[] / realloc()
==17900==    at 0x4C2B75D: free (vg_replace_malloc.c:468)
==17900==    by 0x40086F: main (main.c:69)
==17900==  Address 0x40099f is not stack'd, malloc'd or (recently) free'd
==17900== 
==17900== 
==17900== HEAP SUMMARY:
==17900==     in use at exit: 24 bytes in 1 blocks
==17900==   total heap usage: 1 allocs, 1 frees, 24 bytes allocated
==17900== 
==17900== LEAK SUMMARY:
==17900==    definitely lost: 24 bytes in 1 blocks
==17900==    indirectly lost: 0 bytes in 0 blocks
==17900==      possibly lost: 0 bytes in 0 blocks
==17900==    still reachable: 0 bytes in 0 blocks
==17900==         suppressed: 0 bytes in 0 blocks
==17900== Rerun with --leak-check=full to see details of leaked memory
==17900== 
==17900== For counts of detected and suppressed errors, rerun with: -v
==17900== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)

Answer 1

您错过了strcpy()：

mem_ptr=(char*)malloc(24);
mem_ptr="TEST";

这丢弃了指向已分配空间的唯一指针。当你试图释放"TEST"然后valgrind抱怨它没有分配内存（并且它是正确的）。你已经泄露了你分配的24个字节。

修正：

mem_ptr = (char*)malloc(24);

if (mem_ptr == NULL)
    exit(EXIT_FAILURE);

strcpy(mem_ptr, "TEST");
printf("%s\n", mem_ptr);

free(mem_ptr);