MakeMakefile#check_sizeof

check_sizeof(type, headers = nil, opts = "", &b)

# File tmp/rubies/ruby-3.3.0/lib/mkmf.rb, line 1387
def check_sizeof(type, headers = nil, opts = "", &b)
  typedef, member, prelude = typedef_expr(type, headers)
  prelude << "#{typedef} *rbcv_ptr_;\n"
  prelude = [prelude]
  expr = "sizeof((*rbcv_ptr_)#{"." << member if member})"
  fmt = STRING_OR_FAILED_FORMAT
  checking_for checking_message("size of #{type}", headers), fmt do
    if size = try_constant(expr, prelude, opts, &b)
      $defs.push(format("-DSIZEOF_%s=%s", type.tr_cpp, size))
      size
    end
  end
end

Returns the size of the given type. You may optionally specify additional headers to search in for the type.

If found, a macro is passed as a preprocessor constant to the compiler using the type name, in uppercase, prepended with SIZEOF_, followed by the type name, followed by =X where “X” is the actual size.

For example, if check_sizeof('mystruct') returned 12, then the SIZEOF_MYSTRUCT=12 preprocessor macro would be passed to the compiler.

See also #check_signedness #conftest_source #cc_command #convertible_int also in 4.1 · 4.0 · 3.4 · 3.2 · 3.1 · 3.0

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