Question

I’m profiling a recent program that is dominated with File read. I’m kind of confused on how to interpret the results. If someone could explain to me what these top four functions are, it would help me a lot. Thanks in advance!

  %   cumulative   self              self     total           
 time   seconds   seconds    calls  ms/call  ms/call  name    
 25.00      0.95     0.95                             _Unwind_SjLj_Register
 15.79      1.55     0.60                             std::num_get<char, std::istreambuf_iterator<char, std::char_traits<char> > >::_M_extract_float(std::istreambuf_iterator<char, std::char_traits<char> >, std::istreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, std::_Ios_Iostate&, std::string&) const
 10.26      1.94     0.39                             std::string::_M_mutate(unsigned int, unsigned int, unsigned int)
 10.00      2.32     0.38                             _Unwind_SjLj_Unregister

Answer 1

The first and last are for exception handling; they are generated by the compiler to register objects whose destructors must be called if an exception leaves the current scope. You might be able to avoid calls to these functions if you can restructure your code to avoid throwing exceptions, or calling functions that might throw, during the lifetime of objects with non-trivial destructors. This often isn’t possible, though.

The second is the internal function for parsing a float value from an input stream.

The third is the internal function for resizing a string, perhaps one used internally when parsing the stream.