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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[MNT]: c++11 narrowing error when building for 32 bit targets","articleBody":"### Summary\n\nthis happens because `get_height()` and `get_width()` return an unsigned int, which can be losslessly narrowed into a `ssize_t` in 64 bit targets but not in 32 bit targets\n\n```\nFAILED: [code=1] src/_backend_agg.cpython-313-powerpc-linux-musl.so.p/_backend_agg_wrapper.cpp.o\nclang++ -Isrc/_backend_agg.cpython-313-powerpc-linux-musl.so.p -Isrc -I../src -I../extern/agg24-svn/include -I/usr/include/freetype2 -I/usr/include/libpng16 -I/usr/include/harfbuzz -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include/sysprof-6 -I/usr/share/pkgconfig/../../lib/python3.13/site-packages/pybind11/share/pkgconfig/../../include -I/usr/include/python3.13 -fvisibility=hidden -fvisibility-inlines-hidden -flto -fdiagnostics-color=always -DNDEBUG -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -std=c++17 -O3 -ffile-prefix-map=/builddir/python-matplotlib-3.10.5=. -Wformat -Werror=format-security -ftrivial-auto-var-init=zero -fno-omit-frame-pointer -mtune=G4 -O2 -g1 -fPIC -DWITH_GZFILEOP -pthread -MD -MQ src/_backend_agg.cpython-313-powerpc-linux-musl.so.p/_backend_agg_wrapper.cpp.o -MF src/_backend_agg.cpython-313-powerpc-linux-musl.so.p/_backend_agg_wrapper.cpp.o.d -o src/_backend_agg.cpython-313-powerpc-linux-musl.so.p/_backend_agg_wrapper.cpp.o -c ../src/_backend_agg_wrapper.cpp\n../src/_backend_agg_wrapper.cpp:253:17: error: non-constant-expression cannot be narrowed from type 'unsigned int' to 'int' in initializer list [-Wc++11-narrowing]\n253 | renderer-\u003eget_height(),\n| ^~~~~~~~~~~~~~~~~~~~~~\n../src/_backend_agg_wrapper.cpp:253:17: note: insert an explicit cast to silence this issue\n253 | renderer-\u003eget_height(),\n| ^~~~~~~~~~~~~~~~~~~~~~\n| static_cast\u003cint\u003e( )\n../src/_backend_agg_wrapper.cpp:254:17: error: non-constant-expression cannot be narrowed from type 'unsigned int' to 'int' in initializer list [-Wc++11-narrowing]\n254 | renderer-\u003eget_width(),\n| ^~~~~~~~~~~~~~~~~~~~~\n../src/_backend_agg_wrapper.cpp:254:17: note: insert an explicit cast to silence this issue\n254 | renderer-\u003eget_width(),\n| ^~~~~~~~~~~~~~~~~~~~~\n| static_cast\u003cint\u003e( )\n../src/_backend_agg_wrapper.cpp:258:17: error: non-constant-expression cannot be narrowed from type 'unsigned int' to 'int' in initializer list [-Wc++11-narrowing]\n258 | renderer-\u003eget_width() * 4,\n| ^~~~~~~~~~~~~~~~~~~~~~~~~\n../src/_backend_agg_wrapper.cpp:258:17: note: insert an explicit cast to silence this issue\n258 | renderer-\u003eget_width() * 4,\n| ^~~~~~~~~~~~~~~~~~~~~~~~~\n| static_cast\u003cint\u003e( )\n3 errors generated.\n```\n\nfull build log at https://build.chimera-linux.org/#/builders/7/builds/1457/steps/4/logs/pkg_user_python-matplotlib_3_10_5-r0\n\n### Proposed fix\n\npotentially just adding the static casts as the compiler note says\n```diff\ndiff -ruN a/src/_backend_agg_wrapper.cpp b/src/_backend_agg_wrapper.cpp\n--- a/src/_backend_agg_wrapper.cpp\t2025-07-31 19:00:28.000000000 +0200\n+++ b/src/_backend_agg_wrapper.cpp\t2025-08-10 21:50:30.146295804 +0200\n@@ -250,12 +250,12 @@\n \n         .def_buffer([](RendererAgg *renderer) -\u003e py::buffer_info {\n             std::vector\u003cpy::ssize_t\u003e shape {\n-                renderer-\u003eget_height(),\n-                renderer-\u003eget_width(),\n+                static_cast\u003cpy::ssize_t\u003e(renderer-\u003eget_height()),\n+                static_cast\u003cpy::ssize_t\u003e(renderer-\u003eget_width()),\n                 4\n             };\n             std::vector\u003cpy::ssize_t\u003e strides {\n-                renderer-\u003eget_width() * 4,\n+                static_cast\u003cpy::ssize_t\u003e(renderer-\u003eget_width() * 4),\n                 4,\n                 1\n             };\n```","author":{"url":"https://github.com/z-erica","@type":"Person","name":"z-erica"},"datePublished":"2025-08-10T20:02:21.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/30413/matplotlib/issues/30413"}