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

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

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);
}