method

have_var

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have_var(var, headers = nil, opt = "", &b) public

Returns whether or not the variable var can be found in the common header files, or within any headers that you provide. If found, a macro is passed as a preprocessor constant to the compiler using the variable name, in uppercase, prepended with HAVE_.

To check variables in an additional library, you need to check that library first using have_library().

For example, if have_var(‘foo’) returned true, then the HAVE_FOO preprocessor macro would be passed to the compiler.

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# File lib/mkmf.rb, line 1039
  def have_var(var, headers = nil, opt = "", &b)
    checking_for checking_message(var, headers, opt) do
      if try_var(var, headers, opt, &b)
        $defs.push(format("-DHAVE_%s", var.tr_cpp))
        true
      else
        false
      end
    end
  end

have_var

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