有没有办法验证我的程序没有内存泄漏？ [英] Is there way to verify my program has no memory leaks?
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问题描述
我希望确定以下程序（查找最大子数组的实现）是否泄漏内存。有确定这种情况的一般方法吗？如使用调试器的某些功能？什么是一般策略？
I wish to determine if the following program (an implementation of finding the maximum sub-array) leaks memory. Is there a general way to determine this? Such as using some feature of a debugger? What are general strategies?
struct Interval {
int max_left;
int max_right;
int sum;
};
struct Interval * max_crossing_subarray(int A[], int low, int mid, int high) {
struct Interval * crossing = malloc(sizeof(struct Interval));
int left_sum = INT_MIN;
int sum = 0;
for(int i = mid; i >= low; --i) {
sum = sum + A[i];
if(sum > left_sum) {
left_sum = sum;
crossing->max_left = i;
}
}
int right_sum = INT_MIN;
sum = 0;
for(int j = mid+1; j <= high; ++j) {
sum = sum + A[j];
if(sum > right_sum) {
right_sum = sum;
crossing->max_right = j;
}
}
crossing->sum = left_sum + right_sum;
return crossing;
}
struct Interval * max_subarray(int A[], int low, int high) {
if(high == low) {
struct Interval * base = malloc(sizeof(struct Interval));
*base = (struct Interval) { low, high, A[low] };
return base;
} else {
int mid = floor((low+high)/2);
struct Interval * left = malloc(sizeof(struct Interval));
struct Interval * right = malloc(sizeof(struct Interval));
left = max_subarray(A, low, mid);
right = max_subarray(A, mid+1, high);
struct Interval * cross = max_crossing_subarray(A, low, mid, high);
if(left->sum >= right->sum & right->sum >= cross->sum) {
free(right);
free(cross);
return left;
} else if(right->sum >= left->sum & right->sum >= cross-> sum) {
free(left);
free(cross);
return right;
} else {
free(left);
free(right);
return cross;
}
}
}
int main()
{
int A[] = {-10, 7, -5, -3, 40, 4, -1, 8, -3, -1, -5, 20, 7};
struct Interval * result = max_subarray(A, 0, 12);
printf("left: %i, right: %i, sum: %i\n", result->max_left, result->max_right, result->sum);
return 0;
}
由于该程序具有递归性，因此很难遵循（至少为了我）。我想我已经插入了所有东西，但我想找到一种确定的方法。
Due to the recursive nature of the program it's quite difficult to follow (at least for me). I think I've plugged everything but I'd like to find a methodology for being sure.
编辑：软件建议在选定的答案中，我找到了所有的泄漏，并且正如注释中所指出的，没有理由左右分配，下面是无内存泄漏的代码。
struct Interval {
int max_left;
int max_right;
int sum;
};
struct Interval * max_crossing_subarray(int A[], int low, int mid, int high) {
struct Interval * crossing = malloc(sizeof(struct Interval));
int left_sum = INT_MIN;
int sum = 0;
for(int i = mid; i >= low; --i) {
sum = sum + A[i];
if(sum > left_sum) {
left_sum = sum;
crossing->max_left = i;
}
}
int right_sum = INT_MIN;
sum = 0;
for(int j = mid+1; j <= high; ++j) {
sum = sum + A[j];
if(sum > right_sum) {
right_sum = sum;
crossing->max_right = j;
}
}
crossing->sum = left_sum + right_sum;
return crossing;
}
struct Interval * max_subarray(int A[], int low, int high) {
if(high == low) {
struct Interval * base = malloc(sizeof(struct Interval));
*base = (struct Interval) { low, high, A[low] };
return base;
} else {
int mid = floor((low+high)/2);
struct Interval * left = max_subarray(A, low, mid);
struct Interval * right = max_subarray(A, mid+1, high);
struct Interval * cross = max_crossing_subarray(A, low, mid, high);
if(left->sum >= right->sum & right->sum >= cross->sum) {
free(right);
free(cross);
return left;
} else if(right->sum >= left->sum & right->sum >= cross-> sum) {
free(left);
free(cross);
return right;
} else {
free(left);
free(right);
return cross;
}
}
}
int main()
{
int A[] = {-10, 7, -5, -3, 40, 4, -1, 8, -3, -1, -5, 20, 7};
struct Interval * result = max_subarray(A, 0, 13-1);
printf("left: %i, right: %i, sum: %i\n", result->max_left, result->max_right, result->sum);
return 0;
}
推荐答案
您可以使用 valgrind 。这是用于Linux和其他类似UNIX的系统的内存调试工具，它可以查找内存泄漏以及无效的内存访问。
You can use valgrind. It's a memory debugging tool for Linux and other UNIX-like systems that finds memory leaks as well as invalid memory accesses.
当我通过valgrind运行此代码时，它会输出以下：
When I run this code through valgrind, it outputs the following:
[dbush@db-centos7 ~]$ valgrind ./x1
==3406== Memcheck, a memory error detector
==3406== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==3406== Using Valgrind-3.14.0 and LibVEX; rerun with -h for copyright info
==3406== Command: ./x1
==3406==
left: 4, right: 12, sum: 69
==3406==
==3406== HEAP SUMMARY:
==3406== in use at exit: 300 bytes in 25 blocks
==3406== total heap usage: 49 allocs, 24 frees, 588 bytes allocated
==3406==
==3406== LEAK SUMMARY:
==3406== definitely lost: 300 bytes in 25 blocks
==3406== indirectly lost: 0 bytes in 0 blocks
==3406== possibly lost: 0 bytes in 0 blocks
==3406== still reachable: 0 bytes in 0 blocks
==3406== suppressed: 0 bytes in 0 blocks
==3406== Rerun with --leak-check=full to see details of leaked memory
==3406==
==3406== For counts of detected and suppressed errors, rerun with: -v
==3406== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
所以您有一些泄漏。现在，让我们通过-leak-check = full 选项来查看那些泄漏的确切位置：
So you have some leaks. Now let's pass the --leak-check=full option to see where exactly those leaks are:
==11531== Memcheck, a memory error detector
==11531== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==11531== Using Valgrind-3.14.0 and LibVEX; rerun with -h for copyright info
==11531== Command: ./x1
==11531==
left: 4, right: 12, sum: 69
==11531==
==11531== HEAP SUMMARY:
==11531== in use at exit: 300 bytes in 25 blocks
==11531== total heap usage: 49 allocs, 24 frees, 588 bytes allocated
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 1 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007A8: max_subarray (x1.c:49)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 2 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007B6: max_subarray (x1.c:50)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 3 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007A8: max_subarray (x1.c:49)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 4 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007B6: max_subarray (x1.c:50)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 5 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007A8: max_subarray (x1.c:49)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 6 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007B6: max_subarray (x1.c:50)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 7 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007A8: max_subarray (x1.c:49)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 8 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007B6: max_subarray (x1.c:50)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 9 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007A8: max_subarray (x1.c:49)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 10 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007B6: max_subarray (x1.c:50)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 11 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007A8: max_subarray (x1.c:49)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 12 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007B6: max_subarray (x1.c:50)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 13 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007A8: max_subarray (x1.c:49)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 14 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007B6: max_subarray (x1.c:50)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 15 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007A8: max_subarray (x1.c:49)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 16 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007B6: max_subarray (x1.c:50)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 17 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007A8: max_subarray (x1.c:49)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 18 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007B6: max_subarray (x1.c:50)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 19 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007A8: max_subarray (x1.c:49)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 20 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007B6: max_subarray (x1.c:50)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 21 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007A8: max_subarray (x1.c:49)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 22 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007B6: max_subarray (x1.c:50)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 23 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007A8: max_subarray (x1.c:49)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 24 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x4007B6: max_subarray (x1.c:50)
==11531== by 0x4007CE: max_subarray (x1.c:51)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x4007E9: max_subarray (x1.c:52)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== 12 bytes in 1 blocks are definitely lost in loss record 25 of 25
==11531== at 0x4C29EA3: malloc (vg_replace_malloc.c:309)
==11531== by 0x40065B: max_crossing_subarray (x1.c:13)
==11531== by 0x400802: max_subarray (x1.c:53)
==11531== by 0x400931: main (x1.c:73)
==11531==
==11531== LEAK SUMMARY:
==11531== definitely lost: 300 bytes in 25 blocks
==11531== indirectly lost: 0 bytes in 0 blocks
==11531== possibly lost: 0 bytes in 0 blocks
==11531== still reachable: 0 bytes in 0 blocks
==11531== suppressed: 0 bytes in 0 blocks
==11531==
==11531== For counts of detected and suppressed errors, rerun with: -v
==11531== ERROR SUMMARY: 25 errors from 25 contexts (suppressed: 0 from 0)
这些漏洞大多数即将到来从这两行开始：
Most of these leaks are coming from these two lines:
struct Interval * left = malloc(sizeof(struct Interval));
struct Interval * right = malloc(sizeof(struct Interval));
如果我们看一下下面两行，很明显为什么：
And if we look at the next two lines it's apparent why:
left = max_subarray(A, low, mid);
right = max_subarray(A, mid+1, high);
因此，在将分配的内存地址分配给这些指针之后，立即用其他值覆盖这些地址，造成泄漏。可以通过摆脱 malloc 调用并使用函数调用的结果进行初始化来解决此问题：
So right after you assign the address of allocated memory to these pointers you overwrite those addresses with other values, causing a leak. This can be fixed by getting rid of the malloc calls and initializing with the result of the function calls:
struct Interval * left = max_subarray(A, low, mid);
struct Interval * right = max_subarray(A, mid+1, high);
最后一个在 max_crossing_subarray
struct Interval * crossing = malloc(sizeof(struct Interval));
此指针是从函数返回的，因此我们需要查看丢失的 max_subarray 调用的，最终将其返回为 main 作为结果：
This pointer is returned from the function, so we need to see where the missing free is. After some looking around, we see that it is called from max_subarray, which eventually returns it to main as result:
struct Interval * result = max_subarray(A, 0, 13-1);
printf("left: %i, right: %i, sum: %i\n", result->max_left, result->max_right, result->sum);
return 0;
但是正如您所看到的，没有人呼吁免费 在这里，所以我们添加它：
But as you can see, there's no call to free here, so let's add it:
struct Interval * result = max_subarray(A, 0, 13-1);
printf("left: %i, right: %i, sum: %i\n", result->max_left, result->max_right, result->sum);
free(result);
return 0;
现在，在进行这些修复后，我们将再次通过valgrind进行操作：
Now after making those fixes we'll run through valgrind again:
==11736== Memcheck, a memory error detector
==11736== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==11736== Using Valgrind-3.14.0 and LibVEX; rerun with -h for copyright info
==11736== Command: ./x1
==11736==
left: 4, right: 12, sum: 69
==11736==
==11736== HEAP SUMMARY:
==11736== in use at exit: 0 bytes in 0 blocks
==11736== total heap usage: 25 allocs, 25 frees, 300 bytes allocated
==11736==
==11736== All heap blocks were freed -- no leaks are possible
==11736==
==11736== For counts of detected and suppressed errors, rerun with: -v
==11736== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
泄漏消失了。
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