1 /* $NetBSD: expr_precedence.c,v 1.10 2022/08/25 19:03:48 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+1: error: syntax error '=' [249] */ 34 var = 1, 35 /* Syntactically ok, must be a constant expression though. */ 36 var > 0 ? 2 : 1))) 37 my_printf(const char *, ...); 38 39 void 40 assignment_associativity(int arg) 41 { 42 int left, right; 43 44 /* 45 * Assignments are right-associative. If they were left-associative, 46 * the result of (left = right) would be an rvalue, resulting in this 47 * error message: 'left operand of '=' must be lvalue [114]'. 48 */ 49 left = right = arg; 50 51 left = arg; 52 } 53 54 void 55 conditional_associativity(_Bool cond1, _Bool cond2, int a, int b, int c) 56 { 57 /* The then-expression can be an arbitrary expression. */ 58 var = cond1 ? cond2 ? a : b : c; 59 var = cond1 ? (cond2 ? a : b) : c; 60 61 /* The then-expression can even be a comma-expression. */ 62 var = cond1 ? cond2 ? a, b : (b, a) : c; 63 64 var = cond1 ? a : cond2 ? b : c; 65 /* 66 * In almost all programming languages, '?:' is right-associative, 67 * which allows for easy chaining. 68 */ 69 var = cond1 ? a : (cond2 ? b : c); 70 /* 71 * In PHP, '?:' is left-associative, which is rather surprising and 72 * requires more parentheses to get the desired effect. 73 */ 74 var = (cond1 ? a : cond2) ? b : c; 75 } 76