Simplest way to wrap an "AC_DEFINE_UNQUOTED" output around #ifndef and #endif?

This line for example AC_DEFINE_UNQUOTED([SOME_MACRO_NAME], "$SOME_VALUE", [some comment]) generates printf "%s\n" "#define SOME_MACRO_NAME \"$SOME_VALUE\"" >>confdefs.h as a line in configure. And something like the following in config.h after configure is run: /* some comment */ #define SOME_MACRO_NAME "" How would I make it produce the following instead? /* some comment */ #ifndef SOME_MACRO_NAME #define SOME_MACRO_NAME "" #endif Surely I can add some printf lines manually or create a custom function but shouldn't there be an idiomatic way to do this already? Either methods I mentioned are hackish either way as I'm asserting confdefs.h is the file being temporarily produced. I'm already seeing people would be suggesting testing $SOME_VALUE maybe through AS_IF or m4_if (or any of their applicable variants) instead but that's a varying use case. I might want to have the variable overridable through autoreconf, through ./configure or through CFLAGS with the -D option. It depends. But right now I just want the answer for this. Also somebody might suggest using a template. Please, please no.