Hello, Has this problem already been reported somewhere? GCC 4.2 (default) : GNU gdb 6.3.50-20050815 (Apple version gdb-1346) (Fri Sep 18 20:40:51 UTC 2009) This GDB was configured as "x86_64-apple-darwin".tty /dev/ttys007 run [Switching to process 37957] Running… Hello o oo O oo o (x,y) = ( , ) writing toto, x= : -th step (x,y) = ( , ) (x,y) = ( , ) (x,y) = ( , ) XXXX XXXX _ _ is : _ _, _ _, and __ by default Assertion failed: (s == " 11 22 "), function main, file /usr/local/boost_1_41_0/libs/format/example/sample_formats.cpp, line 76. Program received signal: “SIGABRT”. GCC 4.0 : [Session started at 2010-01-20 20:17:57 -0500.] GDB is free software, covered by the GNU General Public License, and you are This GDB was configured as "x86_64-apple-darwin".tty /dev/ttys007 run [Switching to process 37989] Running… Hello 3 o oo O oo o (x,y) = ( -23, +35) writing toto, x=40.23 : 50-th step (x,y) = ( -23, +35) (x,y) = ( -23, +35) (x,y) = ( -23, +35) XX13 1 XX13 _ 18_ is : _0x12_, _ 022_, and _18_ by default %##0x14 boost::too_many_args: format-string referred to less arguments than were passed ***Dont worry, that was planned boost::too_few_args: format-string referred to more arguments than were passed ***Dont worry, that was planned Everything went OK, exiting.