Thrust快速入門教程（二）——Vector的使用

Trust 提供了兩個vector容器：host_vector 與 device_vector。按照命名規則，host_vector位於主機端，device_vector位於GPU設備端。Trust的vector容器與STL中的容器類似，是通用的容器，可以存儲任何數據類型，可以動態調整大小。以下源代碼展示如何使用Thrust的vector容器。

# include <thrust / host_vector .h>
# include <thrust / device_vector .h>
# include <iostream >
int main ( void )
{
// H has storage for 4 integers
thrust :: host_vector <int > H (4);
// initialize individual elements
H [0] = 14;
H [1] = 20;
H [2] = 38;
H [3] = 46;
// H. size () returns the size of vector H
std :: cout << "H has size " << H. size () << std :: endl ;
// print contents of H
for ( int i = 0; i < H. size (); i ++)
std :: cout << "H[" << i << "] = " << H[i] << std :: endl ;
// resize H
H. resize (2) ;
std :: cout << "H now has size " << H. size () << std :: endl ;
// Copy host_vector H to device_vector D
thrust :: device_vector <int > D = H;
// elements of D can be modified
D [0] = 99;
D [1] = 88;
// print contents of D
for ( int i = 0; i < D. size (); i ++)
std :: cout << "D[" << i << "] = " << D[i] << std :: endl ;
// H and D are automatically deleted when the function returns
return 0;
}

# include <thrust / host_vector .h> # include <thrust / device_vector .h> # include <iostream > int main ( void ) { // H has storage for 4 integers thrust :: host_vector <int > H (4); // initialize individual elements H [0] = 14; H [1] = 20; H [2] = 38; H [3] = 46; // H. size () returns the size of vector H std :: cout << "H has size " << H. size () << std :: endl ; // print contents of H for ( int i = 0; i < H. size (); i ++) std :: cout << "H[" << i << "] = " << H[i] << std :: endl ; // resize H H. resize (2) ; std :: cout << "H now has size " << H. size () << std :: endl ; // Copy host_vector H to device_vector D thrust :: device_vector <int > D = H; // elements of D can be modified D [0] = 99; D [1] = 88; // print contents of D for ( int i = 0; i < D. size (); i ++) std :: cout << "D[" << i << "] = " << D[i] << std :: endl ; // H and D are automatically deleted when the function returns return 0; }  

 

如這個例子所示，運算符”=”可以用來復制host_vector到

device_vector（反之亦然）。 運算符”=”也可以用來復制host_vector到host_vector或device_vector到device_vector。同樣device_vector訪問單個元素可以使用標准的括號表示法。但是，由於每次訪問需要調用cudaMemcpy，應謹慎使用。下面我們將看看一些更有效的技術。

初始化所有向量的元素為特定值、或從一個vector向另一個拷貝特定值，是非常常用的技術。Thrust提供了一些方法可以完成這些種操作。

# include <thrust / host_vector .h>
# include <thrust / device_vector .h>
# include <thrust / copy .h>
# include <thrust / fill .h>
# include <thrust / sequence .h>
# include <iostream >
int main ( void )
{
// initialize all ten integers of a device_vector to 1
thrust :: device_vector <int > D(10 , 1);
// set the first seven elements of a vector to 9
thrust :: fill (D. begin () , D. begin () + 7, 9);
// initialize a host_vector with the first five elements of D
thrust :: host_vector <int > H(D. begin () , D. begin () + 5);
// set the elements of H to 0, 1, 2, 3, ...
thrust :: sequence (H. begin () , H. end ());
// copy all of H back to the beginning of D
thrust :: copy (H. begin () , H. end () , D. begin ());
// print D
for ( int i = 0; i < D. size (); i ++)
std :: cout << "D[" << i << "] = " << D[i] << std :: endl ;
return 0;
}

# include <thrust / host_vector .h> # include <thrust / device_vector .h> # include <thrust / copy .h> # include <thrust / fill .h> # include <thrust / sequence .h> # include <iostream > int main ( void ) { // initialize all ten integers of a device_vector to 1 thrust :: device_vector <int > D(10 , 1); // set the first seven elements of a vector to 9 thrust :: fill (D. begin () , D. begin () + 7, 9); // initialize a host_vector with the first five elements of D thrust :: host_vector <int > H(D. begin () , D. begin () + 5); // set the elements of H to 0, 1, 2, 3, ... thrust :: sequence (H. begin () , H. end ()); // copy all of H back to the beginning of D thrust :: copy (H. begin () , H. end () , D. begin ()); // print D for ( int i = 0; i < D. size (); i ++) std :: cout << "D[" << i << "] = " << D[i] << std :: endl ; return 0; } 

 

這里我們看到了fill、copy、sequence的使用方法。copy函數可以用來拷貝主機端或者設備端的數據到另外一個vector。與STL中的類似，fill用於簡單的向一段元素賦特定值。sequence可以用來生成等差數列。

 

Thrust命名空間

你可能會注意到在我們的例子中使用了thrust::host_vector 或 thrust::copy的字段。其中thrust::告訴編譯器在thrust命名空間中查找函數與類。命名空間是一個很好的方式避免命名重復。例如，thrust::copy就可以與STL中的std::copy區別開來。C++的命名空間允許我們使用這兩個copy函數。