c - *点的动态数组在重新分配后崩溃和泄漏内存 - 为什么？

Question

编辑：为了澄清，我追求的是结构类型的指针数组Point3d。

我搞砸了一些看起来很简单的事情。我在这里阅读了几篇关于动态分配数组的帖子，但我仍然看不出我哪里出错了。

在下面的代码中，我试图创建一个动态分配的 Point3d 结构指针数组。就这样。但是我搞砸了内存分配（valgrind 报告丢失了 40 个字节等），并且当多次重新分配数组时（ALLOC_COUNT > 1）它在释放时崩溃。我在哪里做错了？

我只针对C99。在 Windows 上执行此操作，CLion 在 WSL 上使用 valgrind。

完整的程序：

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

typedef struct Point3d_t {
    double X;
    double Y;
    double Z;
} Point3d;

size_t increment_size = 0;
size_t vertex_count = 0;
size_t current_size = 0;

void *destructVertices(Point3d **vertices) {
    if (vertices != NULL && ((current_size > 0) || (vertex_count > 0))) {
        for (int i = 0; i < current_size; ++i) {
            free(vertices[i]);
            vertices[i] = NULL;
        }
    }
    return NULL;
}

size_t allocateVertices(Point3d **vertices) {
    const size_t new_size = current_size + 1 + increment_size;
    Point3d **expanded_items = realloc(*vertices, new_size * sizeof(Point3d *));
    if (!expanded_items) { // Allocation failed.
        free(*vertices); fprintf(stderr, "RIL: Error reallocating lines array\n");
        expanded_items = NULL; exit(0);
    }
    else if (expanded_items == vertices) {
        expanded_items = NULL; // Same mem addr, no need to change
    }
    else {
        vertices = expanded_items; // mem allocated to new address, point there
    }
    current_size = new_size;
    return current_size;
}

/// returning the last item count, which can also be interpreted
/// as true (>0) or false (0) by the caller
size_t addVertex(Point3d point, Point3d **vertices) {
    if (vertex_count == current_size) {
        if (!allocateVertices(vertices)) return 0;
    }
    Point3d* p = malloc(sizeof(Point3d));
    if (!p) exit(99);
    p->X = point.X;
    p->Y = point.Y;
    p->Z = point.Z;
    vertices[vertex_count] = p;
    vertex_count += 1;
    return vertex_count; // last item count
}

Point3d *m_vertices[1];

将 ALLOC_COUNT 增加到大于 1 的值（导致重新分配）将在解除分配时崩溃。

#define PT_COUNT 4
#define ALLOC_COUNT 1


int main() {
    increment_size = PT_COUNT;
    current_size = 0;
    vertex_count = 0;

    printf("Size of Point3d        = %zu\n", sizeof(Point3d)); // fake error
    printf("Size of *Point3d       = %zu\n", sizeof(Point3d *)); // fake error
    printf("Size of **m_vertices   = %zu\n", sizeof(m_vertices)); // fake error
    printf("Size of *m_vertices    = %zu\n", sizeof(*m_vertices)); // fake error
    printf("Size of *m_vertices[0] = %zu\n", sizeof(*m_vertices[0])); // fake error
    printf("---------------------------\n"); // fake error

    m_vertices[0] = NULL; //malloc(sizeof(Point3d*));

    // new points
    for (int i = 0; i < (PT_COUNT * ALLOC_COUNT); ++i) {
        Point3d p;
        p.X = 1.0 + (i * 0.001);
        p.Y = 2.0 + (i * 0.001);
        p.Z = 3.0 + (i * 0.001);
        const size_t n = addVertex(p, m_vertices);
        if (!n) exit(1);
    }

    printf("vertices.Capacity      = %zu\n", current_size);
    printf("vertices.Count         = %zu\n", vertex_count);

    destructVertices(m_vertices);
    //free(*m_vertices);
    return 0;
}

标签： cmemory-leaks

Answer 1

最终代码（省略了一些 fwd 声明和函数原型）。

如前所述，目的是管理一个动态的指针数组，没有泄漏。用 Valgrind 测试（它只抱怨由 导致的未初始化空间realloc，尽管我实际上分配(void*)NULL给新（重新）分配的空间，但无论如何）。

fn_...省略了一些函数指针原型 ( )。代码风格很奇怪，但我需要从一些现有的 C# 原型中粘贴大量代码，所以我使用 C# 风格部分是为了更容易双向复制粘贴。

typedef struct Point3d_t Point3d;
typedef struct Point3d_t
    double X;
    double Y;
    double Z;
} Point3d;

// This "list owner" was omitted in the OP.
typedef struct MeshVertexList_t {
    size_t AllocationsCount;
    size_t Capacity;
    size_t Count;
    size_t Increment;
    f_Add Add;
    f_allocateVertices allocateVertices;
    f_Destroy Destroy;
    Point3d **Items; // array of ptr
} MeshVertexList;

MeshVertexList *New_MeshVertexList(size_t increment) {
    MeshVertexList *mvlist = malloc(sizeof(MeshVertexList));
    mvlist->AllocationsCount = 0;
    mvlist->Capacity = 0;
    mvlist->Count = 0;
    mvlist->Increment = increment;
    mvlist->Add = Add;
    mvlist->Destroy = Destruct_MeshVertexList;
    mvlist->allocateVertices = allocateVertices;
    mvlist->Items = NULL;
    return mvlist;
}

// Assigned to function pointer
size_t Add(MeshVertexList *self, Point3d *point) {
    if (self->Count == self->Capacity) {
        int res = (int) allocateVertices(self);
        if (!res) return 0;
    }
    self->Items[self->Count] = point;
    self->Count++;
    return self->Count; // last item count
}

// Assigned to function pointer
size_t allocateVertices(MeshVertexList *Vertices) {
    size_t new_capacity = 1;
    if (Vertices->Capacity > 0) new_capacity = Vertices->Capacity + Vertices->Increment;
    void *items_tmp = realloc(Vertices->Items, sizeof(*Vertices->Items) + new_capacity * sizeof(Point3d*));
    if (!items_tmp) {
        Destruct_MeshVertexList(Vertices);
        perror("RIL: Error reallocating lines array\n");
        exit(EXIT_ALLOC_ERROR);
    } else if (items_tmp == Vertices->Items) {
        items_tmp = NULL; // Same mem addr, no need to change
    } else {
        Vertices->Items = items_tmp;
    }
    for (int i = Vertices->Capacity; i < new_capacity; ++i) {
        Vertices->Items[i] = (void *)NULL; // Valgrind doesn't detect this!
    }
    Vertices->AllocationsCount++;
    Vertices->Capacity = new_capacity;
    return Vertices->Capacity;
}

// Assigned to function pointer
void Destruct_MeshVertexList(MeshVertexList *Vertices) {
    for (int i = 0; i <= Vertices->Capacity; ++i) {
        if (Vertices->Items[i] != NULL) {
            free(Vertices->Items[i]); // deallocating point
            Vertices->Items[i] = NULL;
        }
    }
    Vertices->Capacity = 0;
    Vertices->Count = 0;
    Vertices->Increment = 0;
    Vertices->Add = NULL;
    
    Vertices->allocateVertices = NULL;
    free(Vertices->Items);
    Vertices->Items = NULL;
    free(Vertices);
    Vertices = NULL;
}

typedef struct MeshObj_t {
    MeshVertexList *Vertices;
} MeshObj;

#define ALLOC_INCREMENT 1 // <-- debug: realloc for each added pt
#define PT_COUNT 10

int main() {
    const clock_t start = clock();
    MeshObj m;
    m.Vertices = New_MeshVertexList(ALLOC_INCREMENT);
    
    printf("Size of Point3d        = %zu\n", sizeof(Point3d));
    printf("Size of *Point3d       = %zu\n", sizeof(Point3d *));
    printf("Size of m_vertices     = %zu\n", sizeof(m.Vertices));
    //printf("Size of *m_vertices[0] = %zu\n", sizeof(*m_vertices[0]));
    printf("---------------------------\n");
    
    for (int i = 0; i < (PT_COUNT); ++i) {
        Point3d *p = malloc(sizeof(Point3d));
        p->X = 1.0 + (i * 0.001);
        p->Y = 2.0 + (i * 0.001);
        p->Z = 3.0 + (i * 0.001);
        size_t n = m.Vertices->Add(m.Vertices, p);
        p = NULL;
        if (!n) exit(1);
    }

    const clock_t stop = clock();
    const double elapsed_time = (double) (stop - start) / CLOCKS_PER_SEC;
    printf("Vertices->Capacity  : %zu\n", m.Vertices->Capacity);
    printf("Vertices->Count     : %zu\n", m.Vertices->Count);
    printf("Elapsed time        : %lf ms\n", elapsed_time);
    printf("---------------------------\n");
    for (int i = 0; i < m.Vertices->Count; ++i) {
        printf("%f %f %f\n", m.Vertices->Items[i]->X, m.Vertices->Items[i]->Y, m.Vertices->Items[i]->Z);
    }
    
    m.Vertices->Destroy(m.Vertices);
    m.Vertices = NULL;
    return 0;
}