问题
I am an amateur C# programmer who strayed into C++ because of a need for the C++ AMP technology for some heavy-duty number crunching. Hence, my C++ programming skills are not very well developed.
For my first attempt at an actual program, I chose code based on a Daniel Moth's April 2012 article. I cannot get it to build. I always get the error:
C2871 ‘Concurrency’: a namespace with this name does not exist.
I know that the code was first written for Visual Studio 11, but I only had VS 2008 and VS 2010 on my machine. So, I installed VS 2017 (version 15.9.4, .Net 4.7.03062). I started with an empty C++ project but had trouble with it. The best I could do, after I worked through all the things it didn’t recognize, was an error:
C3861: ‘access’ identifier not found, line 2616 in file ‘amp.h’.
So I started again, this time with an empty Windows Console Application project. Again, I had to tweak the code considerably to migrate from Visual Studio 11 to VS 2017, but ended up with code as shown below.
I tried what I could to find the source of the error. I targeted both x64 and x86, but it made no difference. I commented out line 5 and lines 21 – 27, and the code would build and execute. IntelliSense showed no problems, either with identifiers or syntax. In fact, the mouse-over info recognized the Concurrency constructs as such. I deliberately misspelled Concurrency, but IntelliSense caught that right away. I looked through the project properties with an eye toward a setting that needed to be changed to run AMP, but as I wasn’t even sure what I was looking for, I didn’t find anything.
I tried to find the name of the file in which Concurrency is defined, so that I could search my machine to see if it was there, and to add a path if it was, but was unsuccessful. I couldn’t even find the file name. I googled and pored through on-line sources and MS Docs, but no matter how I phrased my search questions, I didn’t find any answers.
The error says:
Concurrency does not exist
which to me means it can’t find it, it’s not on the machine, or some build setting is preventing it from being used. Most of the on-line articles about writing AMP code say nothing about build settings. Does it not require anything different than a serially-coded project? Is it as simple as a missing reference? If so, where do I go to find it? With my limited experience, I don’t know what else to try.
My machine is a Win 7 SP1 box. The KB2999226 bug fix has been installed. I didn’t install all of VS 2017 since I am only interested in C# and C++. Did I fail to install something I should have?
If this problem was addressed before, I couldn’t find it. So, any help would be appreciated.
1. #include <amp.h>
2. #include "pch.h"
3. #include <iostream>
4. #include <vector>
5. using namespace Concurrency;
6.
7. int main() {
8. const int M = 1024; const int N = 1024; //row, col for vector
9. std::vector<int> vA(M*N); std::vector<int> vB(M*N); //vectors to add
10. std::vector<int> vC(M*N); //vector for result
11.
12. for (int i = 0; i < M; i++) { vA[i] = i; } //populate vectors
13. for (int j = N - 1; j >= 0; j--) { vB[j] = j; }
14.
15. for (int i = 0; i < M; i++) { //serial version of
16. for (int j = 0; j < N; j++) { //matrix addition
17. vC[i*N + j] = vA[i*N + j] + vB[i*N + j]; //using vectors
18. }
19. }
20.
21. extent<2> e(M, N); //uses AMP constructs but no
22. array_view<int, 2> a(e, vA), b(e, vB); //parallel functions invoked
23. array_view<int, 2> c(e, vC);
24. index<2> idx(0, 0);
25. for (idx[0] = 0; idx[0] < e[0]; idx[0]++) {
26. for (idx[1] = 0; idx[1] < e[1]; idx[1]++) {
27. c[idx] = a[idx] + b[idx];
28. }
29. }
30. // C2871 'Concurrency': a namespace with this name does not exist. Line 5
31. // Also C2065, C3861, C2062 for all Concurrency objects Line 21 - Line 27
32. }
33.
回答1:
With,
#include "amp.h"
#include "pch.h"
#include <iostream>
using namespace concurrency;
I get,
C2871 'concurrency': a namespace with this name does not exist
However, with,
#include "pch.h"
#include <iostream>
#include "amp.h"
using namespace concurrency;
there is no error.
I suggest moving #include "amp.h" as shown.
I also used both concurrency and Concurrency. There was no difference.
For the error C3861: ‘access’ identifier not found, line 2616 in file ‘amp.h’.
From the menu, select Project, then select Properties.
In the Property Pages window, under C/C++, select All Options, then select Conformance mode.
Change Yes (/permissive-) to No. Select OK.
Build the project and run.
By default, the /permissive- option is set in new projects created by Visual Studio 2017 version 15.5 and later versions. It is not set by default in earlier versions. When the option is set, the compiler generates diagnostic errors or warnings when non-standard language constructs are detected in your code, including some common bugs in pre-C++11 code.
More information may be found here.
This suggests, to me, that "amp.h" is not conforming to the changes made to C++ 15.5. Thus it worked with C++ in VS 2015 14.0 (Update 3), then failed with C++ in VS 2017 15.9.5.
来源：https://stackoverflow.com/questions/54298286/concurrency-a-namespace-with-this-name-does-not-exist