Initial data commit

Task/Call-a-foreign-language-function/D/call-a-foreign-language-function.d

@@ -0,0 +1,36 @@
+import std.stdio: writeln;
+import std.string: toStringz;
+import std.conv: to;
+
+extern(C) {
+    char* strdup(in char* s1);
+    void free(void* ptr);
+}
+
+void main() {
+    // We could use char* here (as in D string literals are
+    // null-terminated) but we want to comply with the "of the
+    // string type typical to the language" part.
+    // Note: D supports 0-values inside a string, C doesn't.
+    auto input = "Hello World!";
+
+    // Method 1 (preferred):
+    //   toStringz converts D strings to null-terminated C strings.
+    char* str1 = strdup(toStringz(input));
+
+    // Method 2:
+    // D strings are not null-terminated, so we append '\0'.
+    // .ptr returns a pointer to the 1st element of the array,
+    // just as &array[0]
+    // This has to be done because D dynamic arrays are
+    // represented with:  { size_t length; T* pointer; }
+    char* str2 = strdup((input ~ '\0').ptr);
+
+    // We could have just used printf here, but the task asks to
+    // "print it using language means":
+    writeln("str1: ", to!string(str1));
+    writeln("str2: ", to!string(str2));
+
+    free(str1);
+    free(str2);
+}