Found the following significant warnings:
  matio/mat5.c:3865:64: warning: format specifies type 'int' but the argument has type 'size_t' (aka 'unsigned long') [-Wformat]
  matio/mat5.c:3891:64: warning: format specifies type 'int' but the argument has type 'size_t' (aka 'unsigned long') [-Wformat]
  matio/mat5.c:3918:64: warning: format specifies type 'int' but the argument has type 'size_t' (aka 'unsigned long') [-Wformat]
  matio/mat5.c:3946:64: warning: format specifies type 'int' but the argument has type 'size_t' (aka 'unsigned long') [-Wformat]
  matio/mat5.c:3973:64: warning: format specifies type 'int' but the argument has type 'size_t' (aka 'unsigned long') [-Wformat]
  matio/mat5.c:3999:64: warning: format specifies type 'int' but the argument has type 'size_t' (aka 'unsigned long') [-Wformat]
  matio/mat5.c:4025:64: warning: format specifies type 'int' but the argument has type 'size_t' (aka 'unsigned long') [-Wformat]
  matio/mat5.c:4051:64: warning: format specifies type 'int' but the argument has type 'size_t' (aka 'unsigned long') [-Wformat]
  matio/mat5.c:4077:64: warning: format specifies type 'int' but the argument has type 'size_t' (aka 'unsigned long') [-Wformat]
  matio/mat5.c:4103:64: warning: format specifies type 'int' but the argument has type 'size_t' (aka 'unsigned long') [-Wformat]
  matio/mat5.c:4158:60: warning: format specifies type 'int' but the argument has type 'size_t' (aka 'unsigned long') [-Wformat]
  matio/mat5.c:4695:34: warning: format specifies type 'int' but the argument has type 'size_t' (aka 'unsigned long') [-Wformat]
  matio/read_data.c:2552:17: warning: format specifies type 'int' but the argument has type 'char *' [-Wformat]
  matio/read_data.c:2552:35: warning: data argument not used by format string [-Wformat-extra-args]
  rmatio.c:3274:18: warning: format string is not a string literal (potentially insecure) [-Wformat-security]
See ‘/home/hornik/tmp/R.check/r-devel-clang/Work/PKGS/rmatio.Rcheck/00install.out’ for details.
* used C compiler: ‘Debian clang version 17.0.5 (1)’