Question

我已经将我的代码简化为最简单的以隔离我的问题，我弄清楚我的问题是什么，但我无法解决它。事实上，我甚至不知道是否有问题。

我有一个函数，用于初始化未初始化的变量并重新初始化已初始化的变量。 我的问题是我声明的变量似乎已初始化。

以下是代码的内容：

/**
  * This software defines the type TabDyn and gives the tools to manipulate it
  * 
  * TabDyn is conceptually an array of integers. The first element is the size while the others are the members of the array.
  *
  * Here are the function provided to manipulate TabDyn :
  *     td_clear(TabDyn* td) : Create the TabDyn object if non existant and initialize it to an empty one. If it exists, it empties it.
  *
  */

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

// TabDyn[0] := size
// tabDyn[i] := i^th element of the array, first index being 1 (i>1)
typedef int* TabDyn;

/**
  * param - TabDyn* td_ptr : address of a declared int
  * void : initialize {td_ptr} to an empty array (size=0, no member)
  */
void td_clear(TabDyn* td_ptr)
{
    //this is the size of each member of TabDyn and thus the size of an empty TabDyn
    size_t TabDynByteCount = sizeof(int); 

    //We must free initialized TabDyn variables
    if(td_ptr && *td_ptr) 
    {
        printf("INITIALIZED!\n"); //#TOREMOVE#
        free(*td_ptr);  
    }

    //Create TabDyn object of size = 0 and give it to param
    *td_ptr = calloc(1, TabDynByteCount);
}

/**
  * Contains various test of the TabDyn function to ensure a correct behaviour by testing it at runtime with Valgrind
  */
int main()
{
    //* TEST decl-init-free #VALID:v0.04#
    printf("\n--- TEST OF td_clear BATCH 1 ---\n");
    printf("Declaring TabDyn variable\n");
    TabDyn tabTestAllocate;
    printf("Initialising TabDyn variable\n");
    td_clear(&tabTestAllocate);
    printf("Freeing now useless variables\n");
    free(tabTestAllocate);
    //*/
    //* TEST decl-init-init-free
    printf("\n--- TEST OF td_clear BATCH 2 ---\n");
    printf("Declaring TabDyn variable\n");
    TabDyn tabTestAllocate2;
    printf("Initialising TabDyn variable\n");
    td_clear(&tabTestAllocate2);
    printf("Re-initialising TabDyn variable\n");
    td_clear(&tabTestAllocate2); // It is not a duplicate
    printf("Freeing now useless variables\n");
    free(tabTestAllocate2);
    //*/
}

这是Valgrind所说的：

--- TEST OF td_clear BATCH 1 ---
Declaring TabDyn variable
Initialising TabDyn variable
==10875== Conditional jump or move depends on uninitialised value(s)
==10875==    at 0x400654: td_clear (in /home/adrien/Documents/c/examen)
==10875==    by 0x4006CD: main (in /home/adrien/Documents/c/examen)
==10875== 
INITIALIZED!
==10875== Conditional jump or move depends on uninitialised value(s)
==10875==    at 0x4C2CDE1: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==10875==    by 0x40066E: td_clear (in /home/adrien/Documents/c/examen)
==10875==    by 0x4006CD: main (in /home/adrien/Documents/c/examen)
==10875== 
==10875== Invalid free() / delete / delete[] / realloc()
==10875==    at 0x4C2CE2B: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==10875==    by 0x40066E: td_clear (in /home/adrien/Documents/c/examen)
==10875==    by 0x4006CD: main (in /home/adrien/Documents/c/examen)
==10875==  Address 0x400540 is in the Text segment of /home/adrien/Documents/c/examen
==10875==    at 0x400540: _start (in /home/adrien/Documents/c/examen)
==10875== 
Freeing now useless variables

--- TEST OF td_clear BATCH 2 ---
Declaring TabDyn variable
Initialising TabDyn variable
==10875== Conditional jump or move depends on uninitialised value(s)
==10875==    at 0x400654: td_clear (in /home/adrien/Documents/c/examen)
==10875==    by 0x40070D: main (in /home/adrien/Documents/c/examen)
==10875== 
INITIALIZED!
==10875== Conditional jump or move depends on uninitialised value(s)
==10875==    at 0x4C2CDE1: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==10875==    by 0x40066E: td_clear (in /home/adrien/Documents/c/examen)
==10875==    by 0x40070D: main (in /home/adrien/Documents/c/examen)
==10875== 
==10875== Invalid free() / delete / delete[] / realloc()
==10875==    at 0x4C2CE2B: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==10875==    by 0x40066E: td_clear (in /home/adrien/Documents/c/examen)
==10875==    by 0x40070D: main (in /home/adrien/Documents/c/examen)
==10875==  Address 0xffefffe70 is on thread 1's stack
==10875== 
Re-initialising TabDyn variable
INITIALIZED!
Freeing now useless variables
==10875== 
==10875== HEAP SUMMARY:
==10875==     in use at exit: 0 bytes in 0 blocks
==10875==   total heap usage: 3 allocs, 5 frees, 12 bytes allocated
==10875== 
==10875== All heap blocks were freed -- no leaks are possible
==10875== 
==10875== For counts of detected and suppressed errors, rerun with: -v
==10875== Use --track-origins=yes to see where uninitialised values come from
==10875== ERROR SUMMARY: 6 errors from 6 contexts (suppressed: 0 from 0)

但如果我将变量显式初始化为NULL，则不再存在任何问题：

 TabDyn tabTestAllocate = NULL;
 TabDyn tabTestAllocate2 = NULL;

我的变量不应该初始化为NULL吗？或者我的if语句没有测试我认为它测试的内容？

Answer 1

不，它们不被支持初始化为NULL，并且它们将具有不确定的值，因为它们具有自动存储持续时间并且未明确初始化。

N1256 6.7.8初始化

10如果没有显式初始化具有自动存储持续时间的对象，则其值为不确定的。

Answer 2

据我所知，初始化时只有静态变量会被设置为NULL。其他变量将指向随机存储器位置，其值存储在该存储器位置中。作为使用C / C ++的程序员，您负责内存使用以及存储在这些位置的内容（内存管理是通常使用的术语）。它不会为你做任何工作。

Answer 3

您的变量（tabTestAllocate）未初始化（请参阅： Why aren't pointers initialized with NULL by default?）。这意味着它的价值未确定。明确定义了它的指针（＆amp; tabTestAllocate）。因此，在if语句中，td_ptr具有已定义的（非NULL）值，而* td_ptr未确定。但这并不意味着* td_ptr应该是NULL，只是你不知道它是什么，所以如果条件是真的你就不能知道apriori。

为什么我的变量没有初始化？

3 个答案: