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Examples of Macros that Fall under PRE00-C-EX5 and not PRE00-C-EX4
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| // The macro ADDRESS_OF reads the L-value of its argument x. | |
| // If ADDRESS_OF were turned into a function, the L-value of | |
| // its argument would change. | |
| // Since it is a macro, this does not happen. | |
| // Therefore, call-by-name semantics are required for ADDRESS_OF | |
| // to function properly. | |
| // This means ADDRESS_OF falls under EX5. | |
| #define ADDRESS_OF(x) (&(x)) | |
| void foo() | |
| { | |
| // ADDRESS_OF is only ever invoked with an argument of type int. | |
| // Therefore, ADDRESS_OF is not used to implement a generic function. | |
| // This means ADDRESS_OF does not fall under EX4. | |
| int x = 0; | |
| int y = 0; | |
| int z = 0; | |
| int *a = ADDRESS_OF(x); | |
| int *b = ADDRESS_OF(y); | |
| int *c = ADDRESS_OF(z); | |
| } |
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| struct node_t | |
| { | |
| struct node_t *next; | |
| }; | |
| // In this example, the macro CONNECT assigns the next member of | |
| // the argument u to the address of the argument v | |
| // CONNECT is not used polymorphically, so it does not fall under EX4. | |
| // CONNECT only works correctly under call-by-name semantics, so it falls under EX5. | |
| #define CONNECT(u, v) (((u)->next) = (&(v))) | |
| void bar() | |
| { | |
| struct node_t x, y, z; | |
| CONNECT(&x, y); | |
| CONNECT(&y, z); | |
| z.next = NULL; | |
| } |
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| #include <string.h> | |
| #define CAP 32 | |
| struct person_t | |
| { | |
| char name[CAP]; | |
| }; | |
| // Assigns the name field of a person_t pointer to the given name | |
| void person_t_set_name(struct person_t *p, char *name) | |
| { | |
| strncpy(p->name, name, CAP); | |
| } | |
| // SET_NAME is defined as an alias for person_t_set_name | |
| // It is only ever invoked with the same types, so it does not fall under EX4. | |
| // It does not behave the same under call-by-value semantics, so it falls under | |
| // EX5. | |
| #define SET_NAME(p, name) (person_t_set_name((&(p)), name)) | |
| void baz() | |
| { | |
| struct person_t p, q, r; | |
| char name[CAP]; | |
| strncpy(name, "Alpha", CAP); | |
| SET_NAME(p, name); | |
| strncpy(name, "Beta", CAP); | |
| SET_NAME(q, name); | |
| strncpy(name, "Gamma", CAP); | |
| SET_NAME(r, name); | |
| } |
Wrap definition of CONNECT in example 2 in parentheses
Add example 3
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Formatting on example 1.
Add example 2.