possibly some code
printf(some_parameters);  // This should match
possibly more code

#ifdef DEBUG
possibly some code
printf(some_parameters);  // This shouldn't match
possibly more code
#endif

possibly some code
printf(some_parameters);  // This should also match
possibly more code

(?<!(#ifdef [A-Å0-9]+)).*printf(.*);.*(?!(#endif))

$ unifdef -UDEBUG file.c | grep printf
printf(some_parameters);  // This should match
printf(some_parameters);  // This should also match

UNIFDEF(1)                BSD General Commands Manual               UNIFDEF(1)

NAME
     unifdef, unifdefall — remove preprocessor conditionals from code

SYNOPSIS
     unifdef [-ceklst] [-Ipath -Dsym[=val] -Usym -iDsym[=val] -iUsym] ... [file]
     unifdefall [-Ipath] ... file

DESCRIPTION
     The unifdef utility selectively processes conditional cpp(1) directives.
     It removes from a file both the directives and any additional text that
     they specify should be removed, while otherwise leaving the file alone.

     The unifdef utility acts on #if, #ifdef, #ifndef, #elif, #else, and #endif
     lines, and it understands only the commonly-used subset of the expression
     syntax for #if and #elif lines.  It handles integer values of symbols
     defined on the command line, the defined() operator applied to symbols
     defined or undefined on the command line, the operators !, <, >, <=, >=,
     ==, !=, &&, ||, and parenthesized expressions.  Anything that it does not
     understand is passed through unharmed.  It only processes #ifdef and
     #ifndef directives if the symbol is specified on the command line, other‐
     wise they are also passed through unchanged.  By default, it ignores #if
     and #elif lines with constant expressions, or they may be processed by
     specifying the -k flag on the command line.

cpp -D<your #define options here> | grep printf