IDA recognizes standard library functions based on IDA's FLIRT libraries. If IDA isn't detecting statically linked standard library functions in your disassembly, it's likely because
- You don't have the correct FLIRT library loaded, or
- IDA doesn't have a FLIRT library for the compiler that created your binary (IDA natively supports these compilers)
You can solve #1 by opening the Type Libraries subview in IDA (View
-> Open subviews
-> Type libraries
) and pressing Ins and choosing the correct compiler.
Alternatively, you can solve #2 by using FLAIR to create your own FLIRT library for the correct compiler.