[c++] Counter exit code 139 when running, but gdb make it through

My question sounds specific, but I doubt it still can be of a C++ debug issue.

I am using omnet++ which is to simulate wireless network. omnet++ itself is a c++ program.

I encountered a queer phenomena when I run my program (modified inet framework with omnet++ 4.2.2 in Ubuntu 12.04): the program exit with exit code 139 (people say this means memory fragmentation) when touching a certain part of the codes, when I try to debug, gdb doesn't report anything wrong with the 'problematic' codes where the simulation exits previously, actually, the debug goes through this part of codes and output expected results.

gdb version info: GNU gdb (Ubuntu/Linaro 7.4-2012.04-0ubuntu2.1) 7.4-2012.04

Could anybody tell me why the run fails but debug doesn't?

Many thanks!

exit code 139 (people say this means memory fragmentation)

No, it means that your program died with signal 11 (SIGSEGV on Linux and most other UNIXes), also known as segmentation fault.

Could anybody tell me why the run fails but debug doesn't?

Your program exhibits undefined behavior, and can do anything (that includes appearing to work correctly sometimes).

Your first step should be running this program under Valgrind, and fixing all errors it reports.

If after doing the above, the program still crashes, then you should let it dump core (ulimit -c unlimited; ./a.out) and then analyze that core dump with GDB: gdb ./a.out core; then use where command.

this error is also caused by null pointer reference. if you are using a pointer who is not initialized then it causes this error.

to check either a pointer is initialized or not you can try something like

Class *pointer = new Class();
if(pointer!=nullptr){
    pointer->myFunction();
}