__attribute__ ((__unused__))

__attribute__((unused))

Specifies that the programmer is aware that a variable or function parameter is not referred to.

Syntax

function-parameter __attribute__((unused));

variable-declaration __attribute__((unused));

variable-definition __attribute__((unused));

Remarks

This attribute specifies that the compiler should not issue a warning for an object if the object is not referred to. This attribute specification has no effect if the compiler's unused warning setting is off.

Listing 19.4 Example of the unused attribute

void f(int a __attribute__((unused))) /* No warning for a. */
{
  int b __attribute__((unused)); /* No warning for b. */
  int c; /* Possible warning for c. */

  return 20;
}

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如  所说：

  此变量属性是 ARM 编译器支持的 GNU 编译器扩展。