clang ++无法使用类型为'int(*)[dim2]'的右值初始化类型为'int(*)[dim2]'的变量 [英] clang++ cannot initialize a variable of type 'int(*)[dim2]' with an rvalue of type 'int (*)[dim2]'

问题描述

为什么要输入代码

void fcn(int *twoDArrayPtr, const int dim1, const int dim2) {
    int (*array)[dim2] = reinterpret_cast<int (*)[dim2]>(twoDArrayPtr);
}

int main() {
    return 0;
}

产生编译器错误

error: cannot initialize a variable of type 'int (*)[dim2]' with
  an rvalue of type 'int (*)[dim2]'

类型相同，所以我认为可以执行分配.由于 int(*)[dim2] 是指向大小为 dim2 的数组的指针，因此可以是指向一堆大小为 dim2 在指针可索引的连续内存中，我认为这应该可行.

The types are the same, so I'd think the assignment can be performed. Since int (*)[dim2] is a pointer to an array of size dim2 and as such could be a pointer to a bunch of arrays of size dim2 in contiguous memory indexable by the pointer, I would think this should work.

我在Mac OS/X上使用clang ++，具有以下版本信息:

I'm using clang++ on Mac OS/X with the following version information:

Apple LLVM version 6.0 (clang-600.0.56) (based on LLVM 3.5svn)
Target: x86_64-apple-darwin14.0.0
Thread model: posix

推荐答案

dim2 不是编译时常量，并且C ++中不存在VLA(可变长度数组).其他一些编译器(例如gcc)具有语言扩展，以允许C ++中的VLA，但是clang的行为符合标准.

dim2 is not a compile-time constant, and VLAs (variable-length arrays) don't exist in C++. Some other compilers (such as gcc) have language extensions to allow VLAs in C++, but clang's behavior is standard-conforming.

您可以使用为您进行地址翻译的类(或类模板)来解决该问题，例如

You can work around the problem with a class (or class template) that does the address translation for you, such as

// This is very rudimentary, but it's a point to start.
template<typename T>
class array2d_ref {
  public:
    array2d_ref(T *p, std::size_t dim) : data_(p), dim_(dim) { }

    T *operator[](std::size_t i) { return &data_[i * dim_]; }

  private:
    T *data_;
    std::size_t dim_;
};

...

array2d_ref<int> array(twoDArrayPtr, dim2);

但是，除非您在编译时就知道数组的尺寸，否则恐怕不可能(便携地)拥有指向数组的指针.

But I'm afraid it is not possible (portably) to have a pointer-to-array unless you know the dimension of the array at compile time.

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