What is the argument for printf that formats a long?

Put an l (lowercased letter L) directly before the specifier.

unsigned long n;
long m;

printf("%lu %ld", n, m);

I think you mean:

unsigned long n;
printf("%lu", n);   // unsigned long

or

long n;
printf("%ld", n);   // signed long

%ld see printf reference on cplusplus.com

I think to answer this question definitively would require knowing the compiler name and version that you are using and the platform (CPU type, OS etc.) that it is compiling for.