Thrust快速入门教程（二）——Vector的使用

Trust 提供了两个vector容器：host_vector 与 device_vector。按照命名规则，host_vector位于主机端，device_vector位于GPU设备端。Trust的vector容器与STL中的容器类似，是通用的容器，可以存储任何数据类型，可以动态调整大小。以下源代码展示如何使用Thrust的vector容器。

# include
# include
# include
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 # include # include int main ( void ) { // H has storage for 4 integers thrust :: host_vector 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 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; } 

 

如这个例子所示，运算符”=”可以用来复制host_vector到

device_vector（反之亦然）。 运算符”=”也可以用来复制host_vector到host_vector或device_vector到device_vector。同样device_vector访问单个元素可以使用标准的括号表示法。但是，由于每次访问需要调用cudaMemcpy，应谨慎使用。下面我们将看看一些更有效的技术。

初始化所有向量的元素为特定值、或从一个vector向另一个拷贝特定值，是非常常用的技术。Thrust提供了一些方法可以完成这些种操作。

# include
# include
# include
# include
# include
# include
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 # include # include # include # include # include int main ( void ) { // initialize all ten integers of a device_vector to 1 thrust :: device_vector 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 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; } 

 

这里我们看到了fill、copy、sequence的使用方法。copy函数可以用来拷贝主机端或者设备端的数据到另外一个vector。与STL中的类似，fill用于简单的向一段元素赋特定值。sequence可以用来生成等差数列。

 

Thrust命名空间

你可能会注意到在我们的例子中使用了thrust::host_vector 或 thrust::copy的字段。其中thrust::告诉编译器在thrust命名空间中查找函数与类。命名空间是一个很好的方式避免命名重复。例如，thrust::copy就可以与STL中的std::copy区别开来。C++的命名空间允许我们使用这两个copy函数。