我有一个 boost::multi_array 的 3 维
boost::multi_array<Struct, 3>* newArr = new boost::multi_array<Struct, 3>(boost::extents[x][y][z], boost::fortran_storage_order())
有没有方法来计算 newArr 的大小，还是应该直接使用
sizeof(Struct)*x*y*z ?
它们会一样吗？ （我希望 multi_array 有一点控制器数据）
【问题讨论】：
你应该可以使用
sizeof(Struct)*x*y*z + sizeof(boost::multi_array<Struct, 3>)
让我搜索一下文档是否揭示了一种更简单/更通用的方法。
另外，我喜欢不打扰并使用例如的输出。 valgrind --tool=massif 确切知道分配在哪里。如果你有，这也会给出相关的结果，例如
struct Struct {
std::string x;
char const* my_data;
};
以下是 Massif 在使用仅带有 std::string 成员的 Struct 时的示例输出：
#include <boost/multi_array.hpp>
struct Struct {
std::string x;
};
int main() {
int x=300,y=400,z=400;
boost::multi_array<Struct, 3>* newArr = new boost::multi_array<Struct, 3>(boost::extents[x][y][z], boost::fortran_storage_order());
}
这会导致例如在我的系统上 384,000,160 字节，这正是您添加 std::cout << 300*400*400*sizeof(Struct)+sizeof(*newArr); 时打印的内容
/tmp$ valgrind --tool=massif --detailed-freq=1 ./test
/tmp$ ms_print massif.out.32149
--------------------------------------------------------------------------------
Command: ./test
Massif arguments: --detailed-freq=1
ms_print arguments: massif.out.32149
--------------------------------------------------------------------------------
MB
366.2^ @
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0 +----------------------------------------------------------------------->Mi
0 1.273
Number of snapshots: 3
Detailed snapshots: [0, 1, 2]
--------------------------------------------------------------------------------
n time(i) total(B) useful-heap(B) extra-heap(B) stacks(B)
--------------------------------------------------------------------------------
0 0 0 0 0 0
00.00% (0B) (heap allocation functions) malloc/new/new[], --alloc-fns, etc.
--------------------------------------------------------------------------------
n time(i) total(B) useful-heap(B) extra-heap(B) stacks(B)
--------------------------------------------------------------------------------
1 1,332,810 168 160 8 0
95.24% (160B) (heap allocation functions) malloc/new/new[], --alloc-fns, etc.
->95.24% (160B) 0x400ADA: main (test.cpp:8)
--------------------------------------------------------------------------------
n time(i) total(B) useful-heap(B) extra-heap(B) stacks(B)
--------------------------------------------------------------------------------
2 1,334,836 384,004,208 384,000,160 4,048 0
100.00% (384,000,160B) (heap allocation functions) malloc/new/new[], --alloc-fns, etc.
->100.00% (384,000,000B) 0x401722: __gnu_cxx::new_allocator<Struct>::allocate(unsigned long, void const*) (new_allocator.h:94)
| ->100.00% (384,000,000B) 0x40138D: boost::multi_array<Struct, 3ul, std::allocator<Struct> >::allocate_space() (multi_array.hpp:474)
| ->100.00% (384,000,000B) 0x400E52: boost::multi_array<Struct, 3ul, std::allocator<Struct> >::multi_array(boost::detail::multi_array::extent_gen<3ul> const&, boost::general_storage_order<3ul> const&) (multi_array.hpp:195)
| ->100.00% (384,000,000B) 0x400AEB: main (test.cpp:8)
|
->00.00% (160B) in 1+ places, all below ms_print's threshold (01.00%)
【讨论】：