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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"ostream::operator\u003c\u003c output shows wrong # of values for 2-d array if strides unusual","articleBody":"The following sample code produces very odd output to cout using `operator\u003c\u003c` in the second case (`doTranspose == 1`):\r\n```\r\n#include \u003ciostream\u003e\r\n#include \u003cvector\u003e\r\n#include \"ndarray.h\"\r\n\r\nint main() {\r\n    // include extra values to avoid reading off the end\r\n    std::vector\u003cdouble\u003e xvec = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20};\r\n\r\n    int const len = 3;\r\n    auto shape1d = ndarray::makeVector(len);\r\n    auto strides1d = ndarray::makeVector(1);\r\n    // create x = {1, 2, 3} and y = {4, 5, 6}\r\n    ndarray::Array\u003cdouble, 1, 1\u003e x = ndarray::external(xvec.data(), shape1d, strides1d);\r\n    ndarray::Array\u003cdouble, 1, 1\u003e y = ndarray::external(xvec.data() + len, shape1d, strides1d);\r\n    std::cout \u003c\u003c \"x = \" \u003c\u003c x \u003c\u003c std::endl;\r\n    std::cout \u003c\u003c \"y = \" \u003c\u003c y \u003c\u003c std::endl;\r\n\r\n    for (int doTranspose = 0; doTranspose \u003c 2; ++doTranspose) {\r\n        auto xyshape = ndarray::makeVector(2, static_cast\u003cint\u003e(x.getSize\u003c0\u003e()));\r\n        std::cout \u003c\u003c \"\\nxyshape = \" \u003c\u003c xyshape \u003c\u003c std::endl;\r\n        auto xystrides = ndarray::makeVector(\u0026y[0] - \u0026x[0], static_cast\u003cstd::ptrdiff_t\u003e(1));\r\n        if (doTranspose) {\r\n            std::cout \u003c\u003c \"transpose xystrides: [[1, 4, 7], [2, 5, 8]]\" \u003c\u003c std::endl;\r\n            xystrides[1] = xystrides[0];\r\n            xystrides[0] = 1;\r\n        } else {\r\n            std::cout \u003c\u003c \"normal xystrides: [[1, 2, 3], [4, 5, 6]])\" \u003c\u003c std::endl;\r\n        }\r\n        std::cout \u003c\u003c \"xystrides = \" \u003c\u003c xystrides \u003c\u003c std::endl;\r\n        ndarray::Array\u003cdouble, 2, 1\u003e xy = ndarray::external(x.getData(), xyshape, xystrides);\r\n        std::cout \u003c\u003c \"xy.getSize\u003c0\u003e() = \" \u003c\u003c xy.getSize\u003c0\u003e() \u003c\u003c \"; xy.getSize\u003c1\u003e() = \" \u003c\u003c xy.getSize\u003c1\u003e() \u003c\u003c std::endl;\r\n\r\n        for (auto row = 0; row \u003c xy.getSize\u003c0\u003e(); ++row) {\r\n            for (int col = 0; col \u003c xy.getSize\u003c1\u003e(); ++col) {\r\n                std::cout \u003c\u003c \"xy[\" \u003c\u003c row \u003c\u003c \"][\" \u003c\u003c col \u003c\u003c \"] = \" \u003c\u003c xy[row][col] \u003c\u003c std::endl;\r\n            }\r\n        }\r\n\r\n        std::cout \u003c\u003c \"xy = \" \u003c\u003c xy \u003c\u003c std::endl;\r\n    }\r\n}\r\n```\r\n\r\nOn my system (clang 8.1.0 on macOS) all output is as expected except the final cout\u003c\u003c, which looks screwy and has far too many values:\r\n```\r\nx = [       1, 2, 3]\r\ny = [       4, 5, 6]\r\n\r\nxyshape = (2,3,)\r\nnormal xystrides: [[1, 2, 3], [4, 5, 6]])\r\nxystrides = (3,1,)\r\nxy.getSize\u003c0\u003e() = 2; xy.getSize\u003c1\u003e() = 3\r\nxy[0][0] = 1\r\nxy[0][1] = 2\r\nxy[0][2] = 3\r\nxy[1][0] = 4\r\nxy[1][1] = 5\r\nxy[1][2] = 6\r\nxy = [[       1, 2, 3], \r\n[       4, 5, 6]]\r\n\r\nxyshape = (2,3,)\r\ntranspose xystrides: [[1, 4, 7], [2, 5, 8]]\r\nxystrides = (1,3,)\r\nxy.getSize\u003c0\u003e() = 2; xy.getSize\u003c1\u003e() = 3\r\nxy[0][0] = 1\r\nxy[0][1] = 4\r\nxy[0][2] = 7\r\nxy[1][0] = 2\r\nxy[1][1] = 5\r\nxy[1][2] = 8\r\nxy = [[       1, 2, 3, 4, 5, 6, 7, 8, 9], \r\n[       2, 3, 4, 5, 6, 7, 8, 9, 10]]\r\n```","author":{"url":"https://github.com/r-owen","@type":"Person","name":"r-owen"},"datePublished":"2017-07-05T20:33:43.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/57/ndarray/issues/57"}