Including a header file from another directory
When referencing to header files relative to your c file you should use #include "path/to/header.h"
The form #include <someheader.h> is only used for internal headers or for explicitly added directories (in gcc with the -I option).
write
#include "../b/structure.h"in place of
#include <structures.h>then go in directory in c & compile your main.c with
gcc main.c
If you work on a Makefile project or simply run your code from command line, use
gcc -IC main.c
where -I option adds your C directory to the list of directories to be searched for header files, so you'll be able to use #include "structures.h"anywhere in your project.