QVector可以存放数据的内存大小是多少？

[shn521]

我试了下，我的电脑可以放60M左右的数据。栈内存是1~2M，堆更大，但vector是在哪分配的内存呢？

[masterz]

应该是堆内存。我的电脑上QVector<__int64>可以放67100000个数据，如果放67200000则失败。

[donwmufromdying]

struct Q_CORE_EXPORT QVectorData
{
    QBasicAtomicInt ref;
    int alloc;
    int size;
#if defined(QT_ARCH_SPARC) && defined(Q_CC_GNU) && defined(__LP64__) && defined(QT_BOOTSTRAPPED)
    // workaround for bug in gcc 3.4.2
    uint sharable;
    uint capacity;
    uint reserved;
#else
    uint sharable : 1;
    uint capacity : 1;
    uint reserved : 30;
#endif

    static QVectorData shared_null;
    // ### Qt 5: rename to 'allocate()'. The current name causes problems for
    // some debugges when the QVector is member of a class within an unnamed namespace.
    // ### Qt 5: can be removed completely. (Ralf)
    static QVectorData *malloc(int sizeofTypedData, int size, int sizeofT, QVectorData *init);
    static QVectorData *allocate(int size, int alignment);
    static QVectorData *reallocate(QVectorData *old, int newsize, int oldsize, int alignment);
    static void free(QVectorData *data, int alignment);
    static int grow(int sizeofTypedData, int size, int sizeofT, bool excessive);
};

看这段代码，你就可以看出，QVector是分配在heap上的。所有容器类一般都是分配在堆上的

[donwmufromdying]

同时，你也可以通过观察这些函数的实现能知道实际的分配和free的过程：

Q_CORE_EXPORT void *qMalloc(size_t size);
Q_CORE_EXPORT void qFree(void *ptr);
Q_CORE_EXPORT void *qRealloc(void *ptr, size_t size);
Q_CORE_EXPORT void *qMallocAligned(size_t size, size_t alignment);
Q_CORE_EXPORT void *qReallocAligned(void *ptr, size_t size, size_t oldsize, size_t alignment);
Q_CORE_EXPORT void qFreeAligned(void *ptr);
Q_CORE_EXPORT void *qMemCopy(void *dest, const void *src, size_t n);
Q_CORE_EXPORT void *qMemSet(void *dest, int c, size_t n);