Improvements to Clang’s diagnostics¶

Clang’s diagnostics are constantly being improved to catch more issues, explain them more clearly, and provide more accurate source information about them. The improvements since the 3.3 release include:

• -Wheader-guard warns on mismatches between the #ifndef and #define lines in a header guard.

  #ifndef multiple
  #define multi
  #endif
  

  returns warning: ‘multiple’ is used as a header guard here, followed by #define of a different macro [-Wheader-guard]

• -Wlogical-not-parentheses warns when a logical not (‘!’) only applies to the left-hand side of a comparison. This warning is part of -Wparentheses.

  int i1 = 0, i2 = 1;
  bool ret;
  ret = !i1 == i2;
  

  returns warning: logical not is only applied to the left hand side of this comparison [-Wlogical-not-parentheses]

• Boolean increment, a deprecated feature, has own warning flag -Wdeprecated-increment-bool, and is still part of -Wdeprecated.

• Clang errors on builtin enum increments and decrements in C++.

  enum A { A1, A2 };
  void test() {
      A a;
      a++;
  }
  

  returns error: cannot increment expression of enum type ‘A’

• -Wloop-analysis now warns on for-loops which have the same increment or decrement in the loop header as the last statement in the loop.

  void foo(char *a, char *b, unsigned c) {
        for (unsigned i = 0; i < c; ++i) {
              a[i] = b[i];
              ++i;
        }
  }
  

  returns warning: variable ‘i’ is incremented both in the loop header and in the loop body [-Wloop-analysis]

• -Wuninitialized now performs checking across field initializers to detect when one field in used uninitialized in another field initialization.

  class A {
    int x;
    int y;
    A() : x(y) {}
  };
  

  returns warning: field ‘y’ is uninitialized when used here [-Wuninitialized]

• Clang can detect initializer list use inside a macro and suggest parentheses if possible to fix.

• Many improvements to Clang’s typo correction facilities, such as:

  • Adding global namespace qualifiers so that corrections can refer to shadowed or otherwise ambiguous or unreachable namespaces.
  • Including accessible class members in the set of typo correction candidates, so that corrections requiring a class name in the name specifier are now possible.
  • Allowing typo corrections that involve removing a name specifier.
  • In some situations, correcting function names when a function was given the wrong number of arguments, including situations where the original function name was correct but was shadowed by a lexically closer function with the same name yet took a different number of arguments.
  • Offering typo suggestions for ‘using’ declarations.
  • Providing better diagnostics and fixit suggestions in more situations when a ‘->’ was used instead of ‘.’ or vice versa.
  • Providing more relevant suggestions for typos followed by ‘.’ or ‘=’.
  • Various performance improvements when searching for typo correction candidates.

• LeakSanitizer is an experimental memory leak detector which can be combined with AddressSanitizer.

C++1y Feature Support¶

Clang 3.4 supports all the features in the current working draft of the upcoming C++ standard, provisionally named C++1y. Support for the following major new features has been added since Clang 3.3:

• Generic lambdas and initialized lambda captures.
• Deduced function return types (auto f() { return 0; }).
• Generalized constexpr support (variable mutation and loops).
• Variable templates and static data member templates.
• Use of ' as a digit separator in numeric literals.
• Support for sized ::operator delete functions.

In addition, [[deprecated]] is now accepted as a synonym for Clang’s existing deprecated attribute.

Use -std=c++1y to enable C++1y mode.

Wide Character Types¶

The ASTContext class now keeps track of two different types for wide character types: WCharTy and WideCharTy. WCharTy represents the built-in wchar_t type available in C++. WideCharTy is the type used for wide character literals; in C++ it is the same as WCharTy, but in C99, where wchar_t is a typedef, it is an integer type.