added example of extending a structure with nested naynonymous declarations

21st_century_c/Makefile

@@ -1,4 +1,4 @@
-CFLAGS = --std=c11 -Wall -O3
+CFLAGS = -Wall -O3 --std=c11
 
 
 boxes : boxes.c
@@ -10,6 +10,9 @@ show_tree : process_dir.h process_dir.c show_tree.c
 simple_cplx : cplx.h complex.c simple_cplx.c
 	$(CC) `pkg-config --cflags --libs gsl` $(CFLAGS) complex.c $@.c -o $@
 
+seamlessone : seamlessone.c
+	$(CC) $(CFLAGS) -fms-extensions -Wno-microsoft $@.c -o $@
+
 .PHONY : all
 all : boxes show_tree simple_cplx
 
@@ -22,4 +25,5 @@ clean :
 	rm -f boxes
 	rm -f show_tree
 	rm -f simple_cplx
+	rm -f seamlessone
 	rm -rf *.dSYM

21st_century_c/seamlessone.c

@@ -0,0 +1,32 @@
+#include <stdio.h>
+#include <math.h>
+
+
+
+typedef struct point {
+  double x, y;
+} point;
+
+
+/*
+Nested anonymous struct declaration compiles with MS extensions only.
+So you have to use -fms-extensions flag with gcc / clang.
+C11 standard allows no typedef in the nested anonymous declaration :(
+*/
+typedef struct {
+  struct point;
+  double z;
+} threepoint;
+
+
+double threelength(threepoint p) {
+  return sqrt(p.x * p.x + p.y * p.y + p.z * p.z);
+}
+
+
+int main () {
+
+  threepoint p = {.x = 3, .y = 0, .z = 4};
+  printf("p is %g units from the origin\n", threelength(p));
+
+}