use strict;
use warnings;

my $data = do {local $/; <DATA>};

our $braces_re = qr/(\{ (?: (?>[^{}]+) | (?-1) )* \})/x;

while ($data =~ /(\{
	(?: (?>(?:(?!\bfopen\b)[^{}])+) | (?> $braces_re ) )* 
	\bfopen\b 
	(?: (?>[^{}]+) | (?> $braces_re ) )* 
\})/xg) {
	print "'$1'\n";
}

__DATA__
void fo
{
	........
	{  //first one
		f = fopen(...);
		.......
		if(...)
		{
		}
	}  //mapping one
	........
}

void bar {
	........
	{  //first one
		if(...) {
			for { if { } else { } }
			f = fopen(...);
			while { }
		}
		.......
		if(...)
		{
		}
	}  //mapping one
	........
}