1 /* $NetBSD: expr_precedence.c,v 1.8 2021/11/16 17:41:23 rillig Exp $ */ 2 # 3 "expr_precedence.c" 3 4 /* 5 * Tests for the precedence among operators. 6 */ 7 8 int var; 9 10 /* 11 * An initializer needs an assignment-expression; the comma must be 12 * interpreted as a separator, not an operator. 13 */ 14 /* expect+1: error: syntax error '4' [249] */ 15 int init_error = 3, 4; 16 17 /* expect+1: error: non-constant initializer [177] */ 18 int init_syntactically_ok = var = 1 ? 2 : 3; 19 20 /* 21 * The arguments of __attribute__ must be constant-expression, as assignments 22 * don't make sense at that point. 23 */ 24 void __attribute__((format(printf, 25 /* 26 * Inside of __attribute__((...)), symbol lookup works differently. For 27 * example, 'printf' is a keyword, and since all arguments to 28 * __attribute__ are constant expressions, looking up global variables 29 * would not make sense. Therefore, 'var' is undefined. 30 * 31 * See lex.c, function 'search', keyword 'in_gcc_attribute'. 32 */ 33 /* expect+2: error: 'var' undefined [99] */ 34 /* expect+1: syntax error '=' [249] */ 35 var = 1, 36 /* Syntactically ok, must be a constant expression though. */ 37 var > 0 ? 2 : 1))) 38 my_printf(const char *, ...); 39 40 void 41 assignment_associativity(int arg) 42 { 43 int left, right; 44 45 /* 46 * Assignments are right-associative. If they were left-associative, 47 * the result of (left = right) would be an rvalue, resulting in this 48 * error message: 'left operand of '=' must be lvalue [114]'. 49 */ 50 left = right = arg; 51 52 left = arg; 53 } 54 55 void 56 conditional_associativity(_Bool cond1, _Bool cond2, int a, int b, int c) 57 { 58 /* The then-expression can be an arbitrary expression. */ 59 var = cond1 ? cond2 ? a : b : c; 60 var = cond1 ? (cond2 ? a : b) : c; 61 62 /* The then-expression can even be a comma-expression. */ 63 var = cond1 ? cond2 ? a, b : (b, a) : c; 64 65 var = cond1 ? a : cond2 ? b : c; 66 /* 67 * In almost all programming languages, '?:' is right-associative, 68 * which allows for easy chaining. 69 */ 70 var = cond1 ? a : (cond2 ? b : c); 71 /* 72 * In PHP, '?:' is left-associative, which is rather surprising and 73 * requires more parentheses to get the desired effect. 74 */ 75 var = (cond1 ? a : cond2) ? b : c; 76 } 77