examples: use std::span (C++20) to plot 2D C-style arrays

Author: amadeus84

examples/span.cpp

@@ -0,0 +1,34 @@
+//
+// g++ -std=c++20 -g -Wall -o span $(python-config --includes) span.cpp $(python-config --ldflags --embed)
+//
+#include "../matplotlibcpp.h"
+
+#include <span>
+
+using namespace std;
+namespace plt = matplotlibcpp;
+
+int main()
+{
+    // C-style arrays with multiple rows
+    time_t t[]={1, 2, 3, 4};
+    int data[]={
+	3, 1, 4, 5,
+	5, 4, 1, 3,
+	3, 3, 3, 3
+    };
+
+    size_t n=sizeof(t)/sizeof(decltype(t[0]));
+    size_t m=sizeof(data)/sizeof(decltype(data[0]));
+
+    // Use std::span to pass data chunk to plot(), without copying it.
+    // Unfortunately, plt::plot() makes an internal copy of both x and y
+    // before passing them to python.
+    for (size_t offset=0; offset<m; offset+=n)
+	plt::plot(t, std::span {data+offset, n}, "");
+    plt::show();
+
+    plt::detail::_interpreter::kill();
+
+    return 0;
+}