复制字符串-我该如何处理内存泄漏和错误情况？

Question

我正在尝试实现函数“ int * cpy_array（int v []，int size）”，该函数将数组复制到另一个数组中并返回新数组作为指针。我还必须提防错误情况并使用动态内存。

好吧，我知道当没有足够的可用内存时，malloc返回0。我想知道是否还有其他可能遗漏的错误。然后，无论成功还是错误，我都必须实现free（）。 我试图实现类似的东西：

 if (!w[i]) { 
 for (k = 0; k < i; ++k)
 free(w[k]); 
 return 0;
}

但是总是有一个错误。 “在hot.c：2包含的文件中： C：/mingw-w64/i686-8.1.0-posix-dwarf-rt_v6-rev0/mingw32/i686-w64-mingw32/include/stdlib.h：502：27：注意：预期为'void *'，但参数为输入“ int””    void __cdecl free（void * _Memory）;而且我不确定为什么要free（）新数组还是应该释放旧数组？我试图在函数中使用指针释放它，但是两者都不起作用，也不认为它应该在主体中？

这是原始代码：

int *cpy_array(int v[], int size);

int main(void)
{
int size; 
size = 4;
int myArray[4] = {1234};
if (*cpy_array(myArray, size) == 0)
{
    printf("No memory available.");
}else{
printf("The new Array: %i", *cpy_array(myArray, size)); 
}

return 0;
}

 int *cpy_array(int v[], int size)
{
    int i;
    int *a  = malloc(size * sizeof(int));
    if(*a == 0)
    return 0;
    for (i = 0; i < size; i++)
    { 
        a[i] = v[i];
    }
return a;
}

Answer 1

在您的第一个代码段中，您错误地重新分配了整数数组w。您不能在该数组中释放单个整数，但是您只需输入：

free(w);

这将释放整个阵列。 您还可以从错误文本中看到-注意：预期为'void *'，但参数的类型为'int'“ void __cdecl free（void * _Memory），该程序预期指向数组的指针而不是整数。

您不能释放旧数组，因为它是静态创建的，并且它的内存是在程序开始时分配的，并且它将在程序本身定义的函数的末尾释放，因此您不必为此担心。释放动态创建的数组（例如通过cpy_array(int v[], int size)函数创建的数组）是您的工作。

有关静态分配和动态分配之间的区别的更多信息，您可以在此处查找：

Difference between static memory allocation and dynamic memory allocation

这部分代码不会正确地打印数组（您将只打印数组的第一个数字），并且您将调用函数两次，这是多余的，对于同一数组只能执行一次

if (*cpy_array(myArray, size) == 0)
{
    printf("No memory available.");
}else{
    printf("The new Array: %i", *cpy_array(myArray, size)); 
}

您可以通过定义一个可以存储该函数返回值的指针来简化这些问题，因此不必调用两次，然后使用for循环正确打印该数组即可。

    int * copiedArray = cpy_array(myArray, size);
    if (copiedArray == NULL)
    {
        printf("No memory available.");
    }else{
        printf("The new Array: ");
        for (int i = 0; i < size; i++)
            printf("%i ", copiedArray[i]); 
    }

我注意到您正在检查指针是否指向某物。进入主程序：

if (*cpy_array(myArray, size) == 0)

然后进入cpy_array(int v[], int size)函数：

if(*a == 0)

这将不起作用，因为您正在取消引用指针并检查其指向的值是否为零。您要做的是检查指针本身的值。如果为NULL，则分配无效：

if (cpy_array(myArray, size) == NULL)

和

 if(a == NULL)

您应该使用NULL而不是零，因为您明确声明要检查指针的值，并且NULL可能不等于每台机器上的零。

有关此主题的更多信息：

What is the difference between NULL, '\0' and 0

Answer 2

要检测与内存有关的问题，请使用 valgrind ，如果我这样做，则会给出：

 <Expander KeyboardNavigation.TabNavigation="None" IsExpanded="False" VerticalAlignment="Top" IsEnabled="True" ExpandDirection="Right" />

“有条件的跳转或移动取决于未初始化的值” 来自==10947== Memcheck, a memory error detector ==10947== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al. ==10947== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info ==10947== Command: ./a.out ==10947== ==10947== Conditional jump or move depends on uninitialised value(s) ==10947== at 0x10548: cpy_array (c.c:25) ==10947== by 0x104B3: main (c.c:11) ==10947== ==10947== Invalid read of size 4 ==10947== at 0x104B8: main (c.c:11) ==10947== Address 0x0 is not stack'd, malloc'd or (recently) free'd ==10947== ==10947== ==10947== Process terminating with default action of signal 11 (SIGSEGV) ==10947== Access not within mapped region at address 0x0 ==10947== at 0x104B8: main (c.c:11) ==10947== If you believe this happened as a result of a stack ==10947== overflow in your program's main thread (unlikely but ==10947== possible), you can try to increase the size of the ==10947== main thread stack using the --main-stacksize= flag. ==10947== The main thread stack size used in this run was 8388608. ==10947== ==10947== HEAP SUMMARY: ==10947== in use at exit: 16 bytes in 1 blocks ==10947== total heap usage: 1 allocs, 0 frees, 16 bytes allocated ==10947== ==10947== 16 bytes in 1 blocks are definitely lost in loss record 1 of 1 ==10947== at 0x4847568: malloc (vg_replace_malloc.c:299) ==10947== by 0x10533: cpy_array (c.c:24) ==10947== by 0x104B3: main (c.c:11) ==10947== ==10947== LEAK SUMMARY: ==10947== definitely lost: 16 bytes in 1 blocks ==10947== indirectly lost: 0 bytes in 0 blocks ==10947== possibly lost: 0 bytes in 0 blocks ==10947== still reachable: 0 bytes in 0 blocks ==10947== suppressed: 0 bytes in 0 blocks ==10947== ==10947== For counts of detected and suppressed errors, rerun with: -v ==10947== Use --track-origins=yes to see where uninitialised values come from ==10947== ERROR SUMMARY: 3 errors from 3 contexts (suppressed: 6 from 3) 中的*a和“大小为4的无效读取。 ”。是因为if(*a == 0)

使您取消引用了0

---

将return 0;更改为if(*a == 0)以解决先前的两个问题，即条件（先验）为假，_valgrind说：

if(a == 0)

所以是的，您有内存泄漏，因为丢失了==11116== Memcheck, a memory error detector ==11116== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al. ==11116== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info ==11116== Command: ./a.out ==11116== Mein neuer Array enthaelt folgende Zeichen: 1==11116== ==11116== HEAP SUMMARY: ==11116== in use at exit: 32 bytes in 2 blocks ==11116== total heap usage: 3 allocs, 1 frees, 1,056 bytes allocated ==11116== ==11116== 16 bytes in 1 blocks are definitely lost in loss record 1 of 2 ==11116== at 0x4847568: malloc (vg_replace_malloc.c:299) ==11116== by 0x10523: cpy_array (c.c:24) ==11116== by 0x104A3: main (c.c:11) ==11116== ==11116== 16 bytes in 1 blocks are definitely lost in loss record 2 of 2 ==11116== at 0x4847568: malloc (vg_replace_malloc.c:299) ==11116== by 0x10523: cpy_array (c.c:24) ==11116== by 0x104CF: main (c.c:15) ==11116== ==11116== LEAK SUMMARY: ==11116== definitely lost: 32 bytes in 2 blocks ==11116== indirectly lost: 0 bytes in 0 blocks ==11116== possibly lost: 0 bytes in 0 blocks ==11116== still reachable: 0 bytes in 0 blocks ==11116== suppressed: 0 bytes in 0 blocks ==11116== ==11116== For counts of detected and suppressed errors, rerun with: -v ==11116== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 6 from 3) 的分配返回的2倍

您需要输入类似以下内容：

cpy_array

进行校正 valgrind 不会发出任何信号：

int * v = cpy_array(myArray, size);

if (*v == 0)
{
  printf("Speicher kann nicht freigegeben werden.");
}else{
  printf("Mein neuer Array enthaelt folgende Zeichen: %i", 
   *v);    
}

free(v);

我鼓励你

• 编译所有警告检测，例如valgrind --leak-check=full ./a.out ==11224== Memcheck, a memory error detector ==11224== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al. ==11224== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info ==11224== Command: ./a.out ==11224== Mein neuer Array enthaelt folgende Zeichen: 1==11224== ==11224== HEAP SUMMARY: ==11224== in use at exit: 0 bytes in 0 blocks ==11224== total heap usage: 2 allocs, 2 frees, 1,040 bytes allocated ==11224== ==11224== All heap blocks were freed -- no leaks are possible ==11224== ==11224== For counts of detected and suppressed errors, rerun with: -v ==11224== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 6 from 3)
• 遇到问题时，请使用 valgrind 和/或调试器
• 即使您在 valgrind 下也看不到问题，所以问题可以隐藏

Answer 3

这不是初始化数组的正确方法

int myArray[4] = {1234};

写

int myArray[4] = { 1,2,3,4 };

或者简单地

int myArray[] = { 1,2,3,4 };

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编写时调用函数cpy_array ..

if (*cpy_array(myArray, size) == 0)   

不正确，为什么？因为如果该函数返回NULL，那么您将取消引用NULL

---

在函数cpy_array中，您取消引用a，这是不正确的，而是比较指针

if ( a == NULL)

，并且将标准常量NULL用于空指针而不是0，因为在所有平台上它可能都不是0。

---