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expr_precedence.c revision 1.11 
      1 /*	$NetBSD: expr_precedence.c,v 1.11 2023/03/28 14:44:34 rillig Exp $	*/
      2 # 3 "expr_precedence.c"
      3 
      4 /*
      5  * Tests for the precedence among operators.
      6  */
      7 
      8 /* lint1-extra-flags: -X 351 */
      9 
     10 int var;
     11 
     12 /*
     13  * An initializer needs an assignment-expression; the comma must be
     14  * interpreted as a separator, not an operator.
     15  */
     16 /* expect+1: error: syntax error '4' [249] */
     17 int init_error = 3, 4;
     18 
     19 /* expect+1: error: non-constant initializer [177] */
     20 int init_syntactically_ok = var = 1 ? 2 : 3;
     21 
     22 /*
     23  * The arguments of __attribute__ must be constant-expression, as assignments
     24  * don't make sense at that point.
     25  */
     26 void __attribute__((format(printf,
     27     /*
     28      * Inside of __attribute__((...)), symbol lookup works differently.  For
     29      * example, 'printf' is a keyword, and since all arguments to
     30      * __attribute__ are constant expressions, looking up global variables
     31      * would not make sense.  Therefore, 'var' is undefined.
     32      *
     33      * See lex.c, function 'search', keyword 'in_gcc_attribute'.
     34      */
     35     /* expect+1: error: syntax error '=' [249] */
     36     var = 1,
     37     /* Syntactically ok, must be a constant expression though. */
     38     var > 0 ? 2 : 1)))
     39 my_printf(const char *, ...);
     40 
     41 void
     42 assignment_associativity(int arg)
     43 {
     44 	int left, right;
     45 
     46 	/*
     47 	 * Assignments are right-associative.  If they were left-associative,
     48 	 * the result of (left = right) would be an rvalue, resulting in this
     49 	 * error message: 'left operand of '=' must be lvalue [114]'.
     50 	 */
     51 	left = right = arg;
     52 
     53 	left = arg;
     54 }
     55 
     56 void
     57 conditional_associativity(_Bool cond1, _Bool cond2, int a, int b, int c)
     58 {
     59 	/* The then-expression can be an arbitrary expression. */
     60 	var = cond1 ? cond2 ? a : b : c;
     61 	var = cond1 ? (cond2 ? a : b) : c;
     62 
     63 	/* The then-expression can even be a comma-expression. */
     64 	var = cond1 ? cond2 ? a, b : (b, a) : c;
     65 
     66 	var = cond1 ? a : cond2 ? b : c;
     67 	/*
     68 	 * In almost all programming languages, '?:' is right-associative,
     69 	 * which allows for easy chaining.
     70 	 */
     71 	var = cond1 ? a : (cond2 ? b : c);
     72 	/*
     73 	 * In PHP, '?:' is left-associative, which is rather surprising and
     74 	 * requires more parentheses to get the desired effect.
     75 	 */
     76 	var = (cond1 ? a : cond2) ? b : c;
     77 }
     78