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expr_sizeof.c revision 1.6 
      1 /*	$NetBSD: expr_sizeof.c,v 1.6 2023/06/28 21:41:27 rillig Exp $	*/
      2 # 3 "expr_sizeof.c"
      3 
      4 /*
      5  * C99 6.5.3.4 "The sizeof operator"
      6  * C11 6.5.3.4 "The sizeof operator"
      7  */
      8 
      9 /* lint1-extra-flags: -X 351 */
     10 
     11 /*
     12  * A sizeof expression can either take a type name or an expression.
     13  */
     14 void sink(unsigned long);
     15 
     16 struct {
     17 	int member;
     18 } s, *ps;
     19 
     20 /*
     21  * In a sizeof expression taking a type name, the type name must be enclosed
     22  * in parentheses.
     23  */
     24 /* expect+1: error: negative array dimension (-4) [20] */
     25 typedef int sizeof_int[-(int)sizeof(int)];
     26 
     27 /*
     28  * In a sizeof expression taking an expression, the expression may or may not
     29  * be enclosed in parentheses, like any other expression.
     30  */
     31 /* expect+1: error: negative array dimension (-4) [20] */
     32 typedef int sizeof_paren_zero[-(int)sizeof(0)];
     33 /* expect+1: error: negative array dimension (-4) [20] */
     34 typedef int sizeof_zero[-(int)sizeof 0];
     35 
     36 /*
     37  * Even though 's' is not a constant expression, 'sizeof s' is.
     38  */
     39 /* expect+1: error: negative array dimension (-4) [20] */
     40 typedef int sizeof_global_var[-(int)sizeof s];
     41 /* expect+1: error: negative array dimension (-4) [20] */
     42 typedef int sizeof_paren_global_var[-(int)sizeof(s)];
     43 
     44 /*
     45  * Even though 'sizeof(s)' may look like a function call expression, the
     46  * parentheses around 's' are ordinary parentheses and do not influence the
     47  * precedence.
     48  *
     49  * Therefore, the '.' following the '(s)' takes precedence over the 'sizeof'.
     50  * Same for the '->' following the '(ps)'.  Same for the '[0]' following the
     51  * '(arr)'.
     52  */
     53 /* expect+1: error: negative array dimension (-4) [20] */
     54 typedef int sizeof_paren_global_struct_member[-(int)sizeof(s).member];
     55 /* expect+1: error: negative array dimension (-4) [20] */
     56 typedef int sizeof_paren_global_ptr_struct_member[-(int)sizeof(ps)->member];
     57 int arr[] = { 1, 2, 3 };
     58 /* expect+1: error: negative array dimension (-3) [20] */
     59 typedef int arr_count[-(int)sizeof(arr) / (int)sizeof(arr)[0]];
     60 
     61 /* FIXME: 'n' is actually used, for the variable length array. */
     62 /* expect+2: warning: argument 'n' unused in function 'variable_length_array' [231] */
     63 void
     64 variable_length_array(int n)
     65 {
     66 	int local_arr[n + 5];
     67 
     68 	/*
     69 	 * Since the array length is not constant, it cannot be used in a
     70 	 * typedef.  Code like this is already rejected by the compiler.  For
     71 	 * simplicity, lint assumes that the array has length 1.
     72 	 */
     73 	/* expect+1: error: negative array dimension (-4) [20] */
     74 	typedef int sizeof_local_arr[-(int)sizeof(local_arr)];
     75 }
     76 
     77 /*
     78  * Ensure that anonymous structs and unions are handled correctly.  They were
     79  * added in C11, and lint did not properly support them until 2023.
     80  */
     81 void
     82 anonymous_struct_and_union(void)
     83 {
     84 	struct {
     85 		union {
     86 			unsigned char uc16[16];
     87 			unsigned char uc32[32];
     88 		};
     89 	} su_16_32;
     90 	/* FIXME: Must be 32, not 48. */
     91 	/* expect+1: error: negative array dimension (-48) [20] */
     92 	typedef int sizeof_su_16_32[-(int)sizeof(su_16_32)];
     93 
     94 	union {
     95 		struct {
     96 			unsigned char uc16[16];
     97 			unsigned char uc32[32];
     98 		};
     99 	} us_16_32;
    100 	/* expect+1: error: negative array dimension (-48) [20] */
    101 	typedef int sizeof_us_16_32[-(int)sizeof(us_16_32)];
    102 }
    103