What happens before main in C++?

by

A lot depends on the execution environment. A great deal of work may be done by the operating system loader before the C run-time start up that is specifically part of your executable runs. This operating system dependent part of setting up the execution environment is common to all native (machine language) executables, regardless of source implementation language.

What part is played by the OS and what is performed by code that is part of your executable differs depending on the execution environment. The OS loader (in a non-standalone system)is responsible for loading the code into memory, and may involve loading and linking dynamically-linked libraries (DLL or shared-libraries depending on the OS nomenclature). Regardless of whether it is an OS or an C-runtime responsibility, the following normally occur:

  • Establishment of a stack
  • Zero initialisation of initialised static data
  • Initialisation of explicitly initialised static data
  • C library initialisation (typically stdio and heap-management require some initialisation)
  • For C++ call static constructors.
  • Creation of the stack frame for main() (argv, argc parameters)

In GCC and some other compilers for example, the part that is performed by your program rather then the OS prior to your program starting, is performed by a separately linked module called crt0.o. This is normally written in assembler and is automatically linked by default.

For further examples and discussion see:

More Related Contents:

  1. c++ error : Segmentation fault (core dumped)
  2. C++ Returning reference to local variable
  3. What do single quotes do in C++ when used on multiple characters?
  4. How can I sort two vectors in the same way, with criteria that uses only one of the vectors?
  5. Why does integer overflow on x86 with GCC cause an infinite loop?
  6. How does `is_base_of` work?
  7. What can I use instead of the arrow operator, `->`?
  8. Will new return NULL in any case?
  9. How do I pass a reference to a two-dimensional array to a function?
  10. Extending the C++ Standard Library by inheritance?
  11. Making std::vector allocate aligned memory
  12. Vector assignment crashing
  13. What are primitive types default-initialized to in C++?
  14. List of standard header files in C and C++
  15. Getting an accurate execution time in C++ (micro seconds)
  16. How to properly uninitialize OpenSSL
  17. How can I determine if a C++ object has been deallocated?
  18. C++ N nested vectors at runtime
  19. C++ & Boost: encode/decode UTF-8
  20. Exception Error c0000005 in VC++
  21. Is it possible to use std::string in a constexpr?
  22. comparison between string literal
  23. C++ Concept that requires a member function with an OutputIterator as parameter
  24. Multi-dimensional vector
  25. How to immediately invoke a C++ lambda?
  26. Is there a functional difference between “2.00” and “2.00f”?
  27. Is “std::cout” usable in Android-ndk
  28. Is codecvt not a std header?
  29. Is there a way to statically-initialize a dynamically-allocated array in C++?
  30. Is there any reason to use C instead of C++ for embedded development? [closed]

Leave a Comment