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PONVidia Thrust Programming with Vectors and Iterators - Basic Questions
 

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  1. PONVidia Thrust Programming with Vectors and Iterators - Basic Questions
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    <p>I'm trying to program something simple in order to learn NVidia CUDA/Thrust. I'm a total noob. What I'm trying to do is use a find_if with a custom predicate. My predicate for the moment just returns true on everything so I'm trying to get all input. I want to do a search eventually for strings where I initialize the functor with some string X and then allow the GPU to find all strings that match. </p> <p>I'm confused on several points here. </p> <p>I try to fill up a device_vector full of pointers to my strings and then run it against my MemCmp predicate. </p> <p>First off, does the device_vector "know" to copy my string over from main memory over to GPU memory or does it just copy a pointer value?</p> <p>Secondly, at the line "count = d_inputVector.end() - iter;" it returns a 12 being the number of items in my iterator that is the result from the find_if. Isn't this wrong? If I try iter - d_inputVector.begin() is returns zero which doesn't get my anywhere. </p> <p>Finally, is my method of getting at the results of my little program correct? Am I to copy memory using thrust::copy into a host_vector and would a loop like the one at the end suffice to view the results?</p> <p>Any suggestions are greatly appreciated. Thanks,</p> <p>mj</p> <pre><code>struct MemCmp { __host__ __device__ bool operator()(char *data) { bool rv = false; rv = true; return rv; } }; .... // I initialize a device_vector and then copy pointers from main memory into the device_vector. thrust::device_vector&lt;char*&gt; d_inputVector( itemCount ); for( int i=0; i&lt;itemCount; i++ ){ d_inputVector[i] = inputData[i]; } thrust::device_vector&lt;char*&gt;::iterator iter; iter = thrust::find_if( d_inputVector.begin(), d_inputVector.end(), MemCmp() ); // this is the count that I think is wrong. count = d_inputVector.end() - iter; thrust::host_vector&lt;char*&gt; results( count ); thrust::copy( d_inputVector.begin(), iter, results.begin() ); for( thrust::host_vector&lt;char *&gt;::iterator it = results.begin(); it != results.end(); it++ ){ char* foo = *it; } </code></pre>
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