#Valgrind + GBD 2017-09-27
- Examples of Memory Errors (undefined behaviour)
- Memeory leaks
- Segmentation fault
- Uninitialized variable access
- Double free
- Mixing new/delete
Valgrind - tool to detect memory errors
- Linux only
- Syntax:
valgrind <args to valgrind> <program> <args to program>
- Definitely lost
- Fix these (usually some memory not having anything pointing to it)
- Indirectly lost
- Probably ignore these (usually some other thing pointing to it is lost)
- Usually the source of the missing data is definitely lost (fixing that usually fixes this)
- Possibly lost
- Treat the same definitely lost for our purposes (very complicated)
- Still reachable
- Still has something pointing to it, but not deallocate when program ends
- For our purposes, always fix
- In the real word: case-by-case, use your judgement
But valgrind doesn't give us line by line information, but luckily we can compile with the arg -g in g++
-g does two things:
- Stores all line information, filename info, ...
- Turns of all optimizations
Now we get information of where memory was allocated but wasn't freed
- It doesn't catch things that are not memory errors
- Bad at helping you find why a problem occured
GDB commands
gdb <args to gdb> program
run <args to prog> < infile > outfile- Run the program
backtrace/bt- Stack trace
print <any C expression- Print the value of expression
up- Goes to the next function in the stack trace
down- Goes the opposite direction of up
break <function name OR file:line>/b- Pause everytime we reach the breakpoint
continue/c- Start running again
next- Move forward one line
step- Move forward one line and step into function calls