C Programming Idioms
====================


Misc Topics
-----------


Attributes
    https://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html#Attribute-Syntax


Variable Arguments
    https://www.cplusplus.com/reference/cstdarg/va_start/


Sys Types
    Defined in <sys/types.c>
    https://man7.org/linux/man-pages/man0/sys_types.h.0p.html



lvalue and rvalues
------------------

lvalue is anything that can appear in the left side of an assigment expression.
More technically, an lvalue is an expression referring to a region of storage.
That includes

#. Named Variables
#. A dereferenced pointer (\*ptr) that does not refer to an array
#. A subscript expression (arx[0]) that does not evaluate to an array
#. A struct Member access (strx -> member) or (strx.member)


the following examplea shows how a function can return an lvalue that can essentially be
treated like an int variables. The memory of such lvalues must be allocated on the heap

.. code-block:: C

    int* create_stuff(){
        int *dtx = malloc(sizeof (int));
        *dtx = 3;
        return dtx;
    }

    #define stuff (*create_stuff())

    int 
    main(int argc, char **argv, char *envp[]){
        printf("k = %d\n",stuff);
        printf("k = %d\n",stuff=10);
        return 0;
    }


This does a similar effect by returning a structure pointer

.. code-block:: C

    struct mystuff {
        int x;
    };

    struct mystuff* create_stuff(){
        struct mystuff *dtx = malloc(sizeof (struct mystuff));
        dtx -> x = 3;
        return dtx;
    }

    #define stuff (create_stuff()->x)

    int 
    main(int argc, char **argv, char *envp[]){
        printf("k = %d\n",stuff);
        printf("k = %d\n",stuff=10);
    }