C++ C++；：从向量中获取T**<；向量<；T>&燃气轮机；
我正在与一个C库接口，它需要一个类型为C++ C++；：从向量中获取T**<；向量<；T>&燃气轮机；,c++,stl,C++,Stl,我正在与一个C库接口，它需要一个类型为float**的2D数组，其大小在运行时确定。我想使用std:：vector之类的STL容器来管理这个内存，但是vector:：data（）给出的是vector*，而不是float**。我能做什么？我会说使用 typedef std::pair<int, int> shape; std::pair<float **, shape> obj; typedef标准：：成对形状； std：：对obj； 或 std:：元组对象； 你喜欢
float**vector:：data（）vector*float**typedef std::pair<int, int> shape;
std::pair<float **, shape> obj;
typedef标准：：成对形状；
std：：对obj；
std:：元组对象；
typedef std::vector<float> FloatVec_t
#include "../../bag/src/dtb_chrono.hh"
#include <iostream>
#include <iomanip>
#include <vector>
#include <cassert>
typedef std::vector<float> FloatVec_t;
class T537_t
{
private:
FloatVec_t fltVec1D;
size_t maxCol;
size_t maxRow;
public:
T537_t () = default;
~T537_t() = default;
int exec(size_t a_MaxCol,
size_t a_MaxRow)
{
maxCol = a_MaxCol;
maxRow = a_MaxRow;
size_t N = maxCol * maxRow;
std::cout << "\n sizeof(float): " << sizeof(float) << std::endl;
std::cout << "\n Col x Row: " << maxCol << " x " << maxRow
<< " = " << N
<< "\n\n reserved " << N << " elements in 1D vec" << std::endl;
fltVec1D.reserve(N);
std::cout << "\n initialize 1D vec with values computed from row and col" << std::flush;
for (uint r=1; r<=maxRow; ++r)
for (uint c=1; c<=maxCol; ++c)
fltVec1D.push_back (100.1F * static_cast<float> (((r-1)*maxCol) + c));
std::cout << "\n\n report fltVec1D addrs: " << std::flush;
for (uint r=0; r<maxRow; ++r)
{
std::cout << "\n fltVec1D[" << std::setw(2) << r << "] " << std::flush;
for (uint c=0; c<maxCol; ++c)
std::cout << " " << std::setw(8)
<< &fltVec1D[indx1D(r,c)] << std::flush;
std::cout << std::flush;
}
std::cout << "\n\n report fltVec1D data: " << std::flush;
for (uint r=0; r<maxRow; ++r)
{
std::cout << "\n fltVec1D[" << std::setw(2) << r << "] " << std::flush;
for (uint c=0; c<maxCol; ++c)
std::cout << " " << std::setw(8) << std::setprecision(5)
<< fltVec1D[indx1D(r,c)] << std::flush;
std::cout << std::flush;
}
// overlay arr on top of fltVec1D data
float** arr = new float* [maxRow]; // arr contains rows
{
for (size_t r=0; r < maxRow; ++r)
arr[r] = getElement(r,0); // rows already exist
} // and start at col 0,
std::cout << "\n\n report arr data: " << std::flush;
for (size_t r=0; r<maxRow; ++r)
{
std::cout << "\n arr[" << std::setw(2) << r << "] " << std::flush;
for (size_t c=0; c<maxCol; ++c)
{
std::cout << " " << std::setw(8) << std::setprecision(5)
<< arr[r][c] << std::flush;
}
std::cout << std::flush;
}
std::cout << "\n\n\n report address diffs: &arr[r][c] - getElement(r,c) : \n" << std::flush;
for (uint r=0; r<maxRow; ++r)
{
std::cout << "\n row" << std::setw(2) << r << " " << std::flush;
for (uint c=0; c<maxCol; ++c)
{
float* addr1 = & arr[r][c];
float* addr2 = getElement(r,c);
std::cout << " " << std::setw(8) << (addr1 - addr2) << std::flush;
}
std::cout << std::flush;
}
delete[] arr; // delete of float** arr = new float* [maxCol];
return 0;
}
private: // methods
size_t indx1D(size_t r, size_t c)
{
assert(r<maxRow);
assert(c<maxCol);
return static_cast<size_t>((r*maxCol) + c);
}
float* getElement(size_t r, size_t c) { return (& fltVec1D [indx1D(r,c) ] ); }
}; // class T537_t
int main(int argc, char* argv[])
{
if(argc > 1)
{
std::cout << "\nargc: " << argc << std::endl;
for (int i = 0; i < argc; i += 1) std::cout << argv[i] << " ";
std::cout << std::endl;
}
if(3 != argc) {
std::cerr << "\n 2 Required parameters: maxCol maxRow " << std::endl;
return (0);
}
setlocale(LC_ALL, "");
std::ios::sync_with_stdio(false);
int retVal = -1;
{
T537_t t537;
Time_t start_us = HRClk_t::now();
retVal = t537.exec(static_cast<size_t>(std::atoi(argv[1])), // col - i.e. 5
static_cast<size_t>(std::atoi(argv[2]))); // row - i.e. 20
auto duration_us = std::chrono::duration_cast<US_t>(HRClk_t::now() - start_us);
std::cout << "\n\n t537.exec() duration " << duration_us.count() << " us" << std::endl;
}
return(retVal);
}
[0, 0] = 1.2
[0, 1] = 3.4
[0, 2] = 5.6
[1, 0] = 7.8
[1, 1] = 9
[1, 2] = 1.2
void new_wrapper_function(std::vector<std::vector<float>>& v)
{
// create a new vector to hold the pointers to the arrays
// managed by the internal vectors
std::vector<float*> v_ptrs;
v_ptrs.reserve(v.size());
// add the addresses of all the arrays to the new vector
std::for_each(std::begin(v), std::end(v)
[&v_ptrs](auto& v){ v_ptrs.push_back(v.data()); });
// call your legacy function using your pointer vector
old_c_function(v_ptrs.data(), v.size(), v.front().size());
}
void新包装函数（std:：vector&v）
{
//创建一个新的向量来保存指向数组的指针
//由内部向量管理
std：：向量v_ptrs；
v_ptrs.reserve（v.size（））；
//将所有数组的地址添加到新向量
标准：：每个（标准：：开始（v），标准：：结束（v）
[&v_ptrs]（自动&v）{v_ptrs.push_back（v.data（））；}）；
//使用指针向量调用遗留函数
旧的_c_函数（v_ptrs.data（），v.size（），v.front（）.size（））；
}
或者（我最喜欢的）构建一个包装器
类float**vector数据（）的指针填充它。你不能免费获得一个float**
，它只是在你选择的数据结构中不存在。我可以问一下为什么我的问题被否决了吗？我尽量简明扼要地问这个问题，并在发帖前进行了广泛的搜索。我怎么能让它变得更好呢？公认的答案既有趣又深刻。不明白为什么这篇文章不受欢迎…这如何帮助将某些东西传递给需要浮点**
？通常当函数文档声称浮点**p
表示mxn 2D数组时，意味着元素是p[i][j]
其中i@aschepler-谢谢你的提问和评论。。我决定提供一些代码，并且必须寻找它，然后修改它。。。。然后，您希望C函数只是有一个草率的声明，并实际将其参数视为float*const*
@aschepler。C函数可以毫无问题地更新数组，指针指向原始数组中的实际数据。将std:：copy
复制到std:：back\u inserter（v）如何
？@aschepler因为我没有复制浮点值，所以我要获取每个内部数组的第一个元素的地址。噢，糟了。std:：vector
无法很好地初始化float*
。不。
#include "../../bag/src/dtb_chrono.hh"
#include <iostream>
#include <iomanip>
#include <vector>
#include <cassert>
typedef std::vector<float> FloatVec_t;
class T537_t
{
private:
FloatVec_t fltVec1D;
size_t maxCol;
size_t maxRow;
public:
T537_t () = default;
~T537_t() = default;
int exec(size_t a_MaxCol,
size_t a_MaxRow)
{
maxCol = a_MaxCol;
maxRow = a_MaxRow;
size_t N = maxCol * maxRow;
std::cout << "\n sizeof(float): " << sizeof(float) << std::endl;
std::cout << "\n Col x Row: " << maxCol << " x " << maxRow
<< " = " << N
<< "\n\n reserved " << N << " elements in 1D vec" << std::endl;
fltVec1D.reserve(N);
std::cout << "\n initialize 1D vec with values computed from row and col" << std::flush;
for (uint r=1; r<=maxRow; ++r)
for (uint c=1; c<=maxCol; ++c)
fltVec1D.push_back (100.1F * static_cast<float> (((r-1)*maxCol) + c));
std::cout << "\n\n report fltVec1D addrs: " << std::flush;
for (uint r=0; r<maxRow; ++r)
{
std::cout << "\n fltVec1D[" << std::setw(2) << r << "] " << std::flush;
for (uint c=0; c<maxCol; ++c)
std::cout << " " << std::setw(8)
<< &fltVec1D[indx1D(r,c)] << std::flush;
std::cout << std::flush;
}
std::cout << "\n\n report fltVec1D data: " << std::flush;
for (uint r=0; r<maxRow; ++r)
{
std::cout << "\n fltVec1D[" << std::setw(2) << r << "] " << std::flush;
for (uint c=0; c<maxCol; ++c)
std::cout << " " << std::setw(8) << std::setprecision(5)
<< fltVec1D[indx1D(r,c)] << std::flush;
std::cout << std::flush;
}
// overlay arr on top of fltVec1D data
float** arr = new float* [maxRow]; // arr contains rows
{
for (size_t r=0; r < maxRow; ++r)
arr[r] = getElement(r,0); // rows already exist
} // and start at col 0,
std::cout << "\n\n report arr data: " << std::flush;
for (size_t r=0; r<maxRow; ++r)
{
std::cout << "\n arr[" << std::setw(2) << r << "] " << std::flush;
for (size_t c=0; c<maxCol; ++c)
{
std::cout << " " << std::setw(8) << std::setprecision(5)
<< arr[r][c] << std::flush;
}
std::cout << std::flush;
}
std::cout << "\n\n\n report address diffs: &arr[r][c] - getElement(r,c) : \n" << std::flush;
for (uint r=0; r<maxRow; ++r)
{
std::cout << "\n row" << std::setw(2) << r << " " << std::flush;
for (uint c=0; c<maxCol; ++c)
{
float* addr1 = & arr[r][c];
float* addr2 = getElement(r,c);
std::cout << " " << std::setw(8) << (addr1 - addr2) << std::flush;
}
std::cout << std::flush;
}
delete[] arr; // delete of float** arr = new float* [maxCol];
return 0;
}
private: // methods
size_t indx1D(size_t r, size_t c)
{
assert(r<maxRow);
assert(c<maxCol);
return static_cast<size_t>((r*maxCol) + c);
}
float* getElement(size_t r, size_t c) { return (& fltVec1D [indx1D(r,c) ] ); }
}; // class T537_t
int main(int argc, char* argv[])
{
if(argc > 1)
{
std::cout << "\nargc: " << argc << std::endl;
for (int i = 0; i < argc; i += 1) std::cout << argv[i] << " ";
std::cout << std::endl;
}
if(3 != argc) {
std::cerr << "\n 2 Required parameters: maxCol maxRow " << std::endl;
return (0);
}
setlocale(LC_ALL, "");
std::ios::sync_with_stdio(false);
int retVal = -1;
{
T537_t t537;
Time_t start_us = HRClk_t::now();
retVal = t537.exec(static_cast<size_t>(std::atoi(argv[1])), // col - i.e. 5
static_cast<size_t>(std::atoi(argv[2]))); // row - i.e. 20
auto duration_us = std::chrono::duration_cast<US_t>(HRClk_t::now() - start_us);
std::cout << "\n\n t537.exec() duration " << duration_us.count() << " us" << std::endl;
}
return(retVal);
}
sizeof(float): 4
Col x Row: 3 x 5 = 15
reserved 15 elements in 1D vec
initialize 1D vec with values computed from row and col
report fltVec1D addrs:
fltVec1D[ 0] 0x179dc50 0x179dc54 0x179dc58
fltVec1D[ 1] 0x179dc5c 0x179dc60 0x179dc64
fltVec1D[ 2] 0x179dc68 0x179dc6c 0x179dc70
fltVec1D[ 3] 0x179dc74 0x179dc78 0x179dc7c
fltVec1D[ 4] 0x179dc80 0x179dc84 0x179dc88
report fltVec1D data:
fltVec1D[ 0] 100.1 200.2 300.3
fltVec1D[ 1] 400.4 500.5 600.6
fltVec1D[ 2] 700.7 800.8 900.9
fltVec1D[ 3] 1001 1101.1 1201.2
fltVec1D[ 4] 1301.3 1401.4 1501.5
report arr data:
arr[ 0] 100.1 200.2 300.3
arr[ 1] 400.4 500.5 600.6
arr[ 2] 700.7 800.8 900.9
arr[ 3] 1001 1101.1 1201.2
arr[ 4] 1301.3 1401.4 1501.5
report address diffs: &arr[r][c] - getElement(r,c) :
row 0 0 0 0
row 1 0 0 0
row 2 0 0 0
row 3 0 0 0
row 4 0 0 0
void old_c_function(float** floats, std::size_t X, std::size_t Y)
{
for(auto x = 0U; x < X; ++x)
for(auto y = 0U; y < Y; ++y)
std::cout << "[" << x << ", " << y << "] = " << floats[x][y] << '\n';
}
int main()
{
std::vector<std::vector<float>> v =
{
{1.2, 3.4, 5.6},
{7.8, 9.0, 1.2},
};
// create a new vector to hold the pointers to the arrays
// managed by the internal vectors
std::vector<float*> v_ptrs;
v_ptrs.reserve(v.size());
// add the addresses of all the arrays to the new vector
std::for_each(std::begin(v), std::end(v),
[&v_ptrs](auto& v){ v_ptrs.push_back(v.data()); });
// call your legacy function using your pointer vector
old_c_function(v_ptrs.data(), v.size(), v.front().size());
}
[0, 0] = 1.2
[0, 1] = 3.4
[0, 2] = 5.6
[1, 0] = 7.8
[1, 1] = 9
[1, 2] = 1.2
void new_wrapper_function(std::vector<std::vector<float>>& v)
{
// create a new vector to hold the pointers to the arrays
// managed by the internal vectors
std::vector<float*> v_ptrs;
v_ptrs.reserve(v.size());
// add the addresses of all the arrays to the new vector
std::for_each(std::begin(v), std::end(v)
[&v_ptrs](auto& v){ v_ptrs.push_back(v.data()); });
// call your legacy function using your pointer vector
old_c_function(v_ptrs.data(), v.size(), v.front().size());
}