1 /* $NetBSD: expr_cast.c,v 1.6 2024/06/08 13:50:47 rillig Exp $ */
2 # 3 "expr_cast.c"
3
4 /*
5 * Tests for value conversion using a cast-expression.
6 *
7 * K&R C does not mention any restrictions on the target type.
8 * C90 requires both the source type and the target type to be scalar.
9 *
10 * GCC allows casting to a struct type but there is no documentation about
11 * it at https://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html. See
12 * c-typeck.c, function build_c_cast, RECORD_OR_UNION_TYPE_P.
13 */
14
15 /* lint1-flags: -Sw -X 351 */
16
17 struct S {
18 int member;
19 };
20
21 struct S
cast(void)22 cast(void)
23 {
24 struct S {
25 double incompatible;
26 } local = {
27 0.0
28 };
29
30 /* expect+2: error: invalid cast from 'struct S' to 'struct S' [147] */
31 /* expect+1: error: function 'cast' expects to return value [214] */
32 return (struct S)local;
33 }
34
35 /*
36 * https://gnats.netbsd.org/22119
37 *
38 * Before 2021-02-28, lint crashed in cast() since the target type of the
39 * cast is NULL.
40 */
41 void
cast_from_error(void)42 cast_from_error(void)
43 {
44 void (*f1)(void);
45
46 /* expect+1: error: 'p' undefined [99] */
47 f1 = (void (*)(void))p;
48 /* expect+2: error: function returns illegal type 'function(void) returning pointer to void' [15] */
49 /* expect+1: error: invalid cast from 'int' to 'function() returning pointer to function(void) returning pointer to void' [147] */
50 f1 = (void *()(void))p; /* crash before 2021-02-28 */
51 }
52
53 /*
54 * Pointer casts had been valid lvalues in GCC before 4.0.
55 *
56 * https://gcc.gnu.org/onlinedocs/gcc-3.4.6/gcc/Lvalues.html#Lvalues
57 *
58 * C99 6.5.4 "Cast operators" footnote 85 says "A cast does not yield an
59 * lvalue".
60 */
61
62 void take_ptr(const void *);
63
64 void *
lvalue_cast(void * p)65 lvalue_cast(void *p)
66 {
67 struct str {
68 int member;
69 };
70
71 /* expect+2: error: a cast does not yield an lvalue [163] */
72 /* expect+1: error: left operand of '=' must be lvalue [114] */
73 ((struct str *)p) = 0;
74
75 /* expect+2: error: a cast does not yield an lvalue [163] */
76 /* expect+1: error: operand of '&' must be lvalue [114] */
77 take_ptr(&(const void *)p);
78
79 return p;
80 }
81