src/common/macros.h

   1 /*
   2  * SPDX-License-Identifier: MIT
   3  *
   4  * Copyright 2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  */
   6
   7 #ifndef _BABELTRACE_INTERNAL_H
   8 #define _BABELTRACE_INTERNAL_H
   9
  10 #ifdef __cplusplus
  11 extern "C" {
  12 #endif
  13
  14 #define bt_max_t(type, a, b)    \
  15         ((type) (a) > (type) (b) ? (type) (a) : (type) (b))
  16
  17 /*
  18  * BT_HIDDEN: set the hidden attribute for internal functions
  19  * On Windows, symbols are local unless explicitly exported,
  20  * see https://gcc.gnu.org/wiki/Visibility
  21  */
  22 #if defined(_WIN32) || defined(__CYGWIN__)
  23 #define BT_HIDDEN
  24 #else
  25 #define BT_HIDDEN __attribute__((visibility("hidden")))
  26 #endif
  27
  28 /*
  29  * Yield `ref`'s value while setting `ref` to NULL.
  30  *
  31  * This can be used to give a strong reference to a callee:
  32  *
  33  *   add_foo_to_list(list, BT_MOVE_REF(foo));
  34  *
  35  * or in a simple assignment:
  36  *
  37  *   my_struct->foo = BT_MOVE_REF(foo);
  38  *
  39  * When moving a reference in a function call, the reference is given to the
  40  * callee even if that function call fails, so make sure the called function
  41  * is written accordingly.
  42  */
  43
  44 #define BT_MOVE_REF(ref)                \
  45         ({                              \
  46                 __typeof__(ref) _ref = ref;     \
  47                 ref = NULL;             \
  48                 _ref;                   \
  49         })
  50
  51 /*
  52  * Copied from:
  53  * <https://stackoverflow.com/questions/37411809/how-to-elegantly-fix-this-unused-variable-warning/37412551#37412551>:
  54  *
  55  * * sizeof() ensures that the expression is not evaluated at all, so
  56  *   its side-effects don't happen. That is to be consistent with the
  57  *   usual behaviour of debug-only constructs, such as assert().
  58  *
  59  * * `((_expr), 0)` uses the comma operator to swallow the actual type
  60  *   of `(_expr)`. This is to prevent VLAs from triggering evaluation.
  61  *
  62  * * `(void)` explicitly ignores the result of `(_expr)` and sizeof() so
  63  *   no "unused value" warning appears.
  64  */
  65
  66 #define BT_USE_EXPR(_expr)              ((void) sizeof((void) (_expr), 0))
  67 #define BT_USE_EXPR2(_expr1, _expr2)                                    \
  68         ((void) sizeof((void) (_expr1), (void) (_expr2), 0))
  69 #define BT_USE_EXPR3(_expr1, _expr2, _expr3)                            \
  70         ((void) sizeof((void) (_expr1), (void) (_expr2), (void) (_expr3), 0))
  71 #define BT_USE_EXPR4(_expr1, _expr2, _expr3, _expr4)                    \
  72         ((void) sizeof((void) (_expr1), (void) (_expr2),                \
  73                 (void) (_expr3), (void) (_expr4), 0))
  74 #define BT_USE_EXPR5(_expr1, _expr2, _expr3, _expr4, _expr5)            \
  75         ((void) sizeof((void) (_expr1), (void) (_expr2),                \
  76                 (void) (_expr3), (void) (_expr4), (void) (_expr5), 0))
  77
  78 #ifdef __cplusplus
  79 }
  80 #endif
  81
  82 #endif