Debugging C++

Library dependencies

macOS: otool -L <executable> to list shared libraries linked to an executable.
Linux: ldd <executable> to list shared libraries linked to an executable.
nm <executable> | grep LZ4_compress_fast to check if a specific symbol is present in the binary.
nm -u <executable> to list undefined symbols in the binary. Notice: this may include symbols from libraries that are not linked to the binary, but are available in the system.

Using lldb (MacOS)

Start lldb with the executable:
```
lldb my_executable
```

Set breakpoints. Can use quotes and parameters or add line numbers, use conditions (-c) Notice that if the function is inside a shared object, you may need to load the shared library first (e.g. with process launch).

break set -n my_function_name
break set -n 'hipo_output::writeHeader(outputContainer*, std::map<std::string, double>, gBank)'
break set --file hipo_output.cc --line <line_number>
break set -n "GOptions::getVerbosityFor" -c "tag.size() == 0"

Run the program with arguments¹:
```
process launch -- arg1 arg2 ...
```

Step through the code:

step        # or just 's'. Step into the next line of code
next        # or just 'n'. Step over the next line of code
frame info  # Show current frame information
list        # Show the current source code around the current line
bt          # Backtrace to see the call stack
bt all      # Full backtrace with arguments
finish      # Step out of the current function

Inspect / Print variable values:

frame variable    # show all variables in the current frame
p variable_name   # print a specific variable value
p *variable_name  # if they're pointers

Using gdb (Linux)

Start gdb with the executable:

gdb my_executable

Set breakpoints (can use function names, file:line, or conditions):

break my_function_name
break 'hipo_output::writeHeader(outputContainer*, std::map<std::string, double>, gBank)'
break hipo_output.cc:<line_number>
break GOptions::getVerbosityFor if tag.size() == 0

Run the program with arguments:

run arg1 arg2 ...

Step through the code:

step     # Step into the next line (enter function)
next     # Step over the next line (skip into function)
finish   # Step out of the current function

Inspect program state:

backtrace       # Show call stack
info locals     # Show local variables
info args       # Show function arguments
print var       # Print value of variable
print *ptr      # Dereference a pointer
list            # Show source around current line

For simpler lldb options run arg1 arg2 also works, but process launch is more flexible. ↩