Several reasons when object files are big

There can be several reasons when object files are bigger than they have to be at minimum:

• statically including dependent libraries
• building with debug information
• building with profiling information
• creating (extremely) complex data structures using templates (maybe recursive boost-structures)
• not turning on optimizing flags while compiling (saves not that much and can cause difficulties if used too extremely)

At first I suggest to check if you're building with debug information, this causes the most bloat in my experience.