warn-unused-result.cpp revision 0e2c34f92f00628d48968dfea096d36381f494cb 
1// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 %s
2
3int f() __attribute__((warn_unused_result));
4
5struct S {
6  void t() const;
7};
8S g1() __attribute__((warn_unused_result));
9S *g2() __attribute__((warn_unused_result));
10S &g3() __attribute__((warn_unused_result));
11
12void test() {
13  f(); // expected-warning {{ignoring return value}}
14  g1(); // expected-warning {{ignoring return value}}
15  g2(); // expected-warning {{ignoring return value}}
16  g3(); // expected-warning {{ignoring return value}}
17
18  (void)f();
19  (void)g1();
20  (void)g2();
21  (void)g3();
22
23  if (f() == 0) return;
24
25  g1().t();
26  g2()->t();
27  g3().t();
28
29  int i = f();
30  S s1 = g1();
31  S *s2 = g2();
32  S &s3 = g3();
33  const S &s4 = g1();
34}
35
36struct X {
37 int foo() __attribute__((warn_unused_result));
38};
39
40void bah() {
41  X x, *x2;
42  x.foo(); // expected-warning {{ignoring return value}}
43  x2->foo(); // expected-warning {{ignoring return value}}
44}
45
46namespace warn_unused_CXX11 {
47struct [[clang::warn_unused_result]] Status {
48  bool ok() const;
49  Status& operator=(const Status& x);
50  inline void Update(const Status& new_status) {
51    if (ok()) {
52      *this = new_status; //no-warning
53    }
54  }
55};
56Status DoSomething();
57Status& DoSomethingElse();
58Status* DoAnotherThing();
59Status** DoYetAnotherThing();
60void lazy() {
61  Status s = DoSomething();
62  if (!s.ok()) return;
63  Status &rs = DoSomethingElse();
64  if (!rs.ok()) return;
65  Status *ps = DoAnotherThing();
66  if (!ps->ok()) return;
67  Status **pps = DoYetAnotherThing();
68  if (!(*pps)->ok()) return;
69
70  (void)DoSomething();
71  (void)DoSomethingElse();
72  (void)DoAnotherThing();
73  (void)DoYetAnotherThing();
74
75  DoSomething(); // expected-warning {{ignoring return value}}
76  DoSomethingElse(); // expected-warning {{ignoring return value}}
77  DoAnotherThing(); // expected-warning {{ignoring return value}}
78  DoYetAnotherThing();
79}
80}
81
82namespace PR17587 {
83struct [[clang::warn_unused_result]] Status;
84
85struct Foo {
86  Status Bar();
87};
88
89struct Status {};
90
91void Bar() {
92  Foo f;
93  f.Bar(); // expected-warning {{ignoring return value}}
94};
95
96}
97
98namespace PR18571 {
99// Unevaluated contexts should not trigger unused result warnings.
100template <typename T>
101auto foo(T) -> decltype(f(), bool()) { // Should not warn.
102  return true;
103}
104
105void g() {
106  foo(1);
107}
108}
109
110namespace std {
111class type_info { };
112}
113
114namespace {
115// The typeid expression operand is evaluated only when the expression type is
116// a glvalue of polymorphic class type.
117
118struct B {
119  virtual void f() {}
120};
121
122struct D : B {
123  void f() override {}
124};
125
126struct C {};
127
128void g() {
129  // The typeid expression operand is evaluated only when the expression type is
130  // a glvalue of polymorphic class type; otherwise the expression operand is not
131  // evaluated and should not trigger a diagnostic.
132  D d;
133  C c;
134  (void)typeid(f(), c); // Should not warn.
135  (void)typeid(f(), d); // expected-warning {{ignoring return value}} expected-warning {{expression with side effects will be evaluated despite being used as an operand to 'typeid'}}
136
137  // The sizeof expression operand is never evaluated.
138  (void)sizeof(f(), c); // Should not warn.
139
140   // The noexcept expression operand is never evaluated.
141  (void)noexcept(f(), false); // Should not warn.
142}
143}
144