c++ - Valgrind，即使我有空， block 也肯定会丢失？

Question

Small Note, Please Ignore the use of malloc instead of new and the use of my own containers instead of vector etc... The point of this code was to practice the basics.

当我运行 Valgrind 时，我得到:

==24855== HEAP SUMMARY:
==24855==     in use at exit: 0 bytes in 2 blocks
==24855==   total heap usage: 12,999 allocs, 12,997 frees, 675,432 bytes allocated
==24855==
==24855== 0 bytes in 1 blocks are definitely lost in loss record 1 of 2
==24855==    at 0x4C29F73: malloc (vg_replace_malloc.c:309)
==24855==    by 0x4014ED: ImageTagger::GetAllSegmentsByLabel(int, int**, int**, int*) (ImageTagger.cpp:100)
==24855==    by 0x402EB6: GetAllSegmentsByLabel (library2.cpp:59)
==24855==    by 0x403A8B: OnGetAllSegmentssByLabel (main2.cpp:345)
==24855==    by 0x4033A6: parser (main2.cpp:172)
==24855==    by 0x403135: main (main2.cpp:95)
==24855==

但是分配的 block 在main中被释放了，这是什么问题？这是我的代码的相关部分:

ImageTagger.cpp:

StatusType ImageTagger::GetAllSegmentsByLabel(int label, int **images, int **segments, int *numOfSegments) {
    if (label <= 0 || images == nullptr || segments == nullptr || numOfSegments == nullptr) {
        return INVALID_INPUT;
    }
    *numOfSegments = Match_Num(image_tree->root, label);
    int *imageArr = (int *) malloc(sizeof(int) * (*numOfSegments));
    if (imageArr == nullptr) {
        return ALLOCATION_ERROR;
    }
    int *segArr = (int *) malloc(sizeof(int) * (*numOfSegments));
    if (segArr == nullptr) {
        free(imageArr);
        return ALLOCATION_ERROR;
    }
    int counter = 0;
    InorderTraversal(image_tree->root, imageArr, segArr, &counter, (*numOfSegments), label);
    *images = imageArr;
    *segments = segArr;
    if ((*numOfSegments) == 0) {
        *images = *segments = nullptr;
    }
    return SUCCESS;
}

在 main2.cpp 中我有(注意最后的两个空闲行，它是如何丢失的？):

static errorType OnGetAllSegmentssByLabel(void* DS, const char* const command) {
    int courseID, numOfLabels;
    int *images, *segments;
    ValidateRead(sscanf(command, "%d", &courseID), 1, "%s failed.\n", commandStr[GETALLSEGMENTSSBYLABEL_CMD]);
    StatusType res = GetAllSegmentsByLabel(DS, courseID, &images, &segments, &numOfLabels);

    free(images);
    free(segments);

    return error_free;
}

Answer 1

如果 GetAllSegmentsByLabel 中的 (*numOfSegments) == 0 为 true，会发生什么？

在这种情况下，您仍然分配了 2 个 0 字节的 block ，并且它们会丢失，因为您在 if 语句中退出函数之前将两个指针都设置为 nullptr。

必须释放包括 malloc(0) 在内的每个 malloc。