Why is initialization of a new variable by itself valid? [duplicate]

by

It’s syntactically valid, since the variable’s point of declaration comes before its initialiser, and the name is available anywhere after that point. This allows less dodgy initialisations like

void *p = &p;

which legitimately uses the name (but not the value) of the variable being initialised.

It’s behaviourally invalid, since using the value of an uninitialised object gives undefined behaviour. That’s not an error that requires diagnosis (since, in general, it can be difficult or impossible to analyse the program flow to see whether an object has been initialised), but as you note, many compilers will give a warning for straightforward cases like this.

More Related Contents:

  1. Does initialization entail lvalue-to-rvalue conversion? Is `int x = x;` UB?
  2. Uninitialized variable behaviour in C++
  3. Using newly declared variable in initialization (int x = x+1)?
  4. Is reading an indeterminate value undefined behavior?
  5. Fun with uninitialized variables and compiler (GCC)
  6. Undefined, unspecified and implementation-defined behavior
  7. Is segmentation fault actual undefined behavior when we refer to a non-static data-member
  8. What is the easiest way to initialize a std::vector with hardcoded elements?
  9. Is signed integer overflow still undefined behavior in C++?
  10. Finding C++ static initialization order problems
  11. Detecting signed overflow in C/C++
  12. Why does this loop produce “warning: iteration 3u invokes undefined behavior” and output more than 4 lines?
  13. Why does integer overflow on x86 with GCC cause an infinite loop?
  14. static initialization order fiasco
  15. If a function returns no value, with a valid return type, is it okay to for the compiler to return garbage?
  16. Object creation on the stack/heap?
  17. C++11: Correct std::array initialization?
  18. Does the ‘offsetof’ macro from invoke undefined behaviour?
  19. Are multiple mutations of the same variable within initializer lists undefined behavior pre C++11
  20. Access array beyond the limit in C and C++ [duplicate]
  21. Now that we have std::array what uses are left for C-style arrays?
  22. C++: Where to initialize variables in constructor [duplicate]
  23. So why is i = ++i + 1 well-defined in C++11?
  24. Program behaving strangely on online IDEs
  25. Is left and right shifting negative integers defined behavior?
  26. Different ways of initializing an object in c++
  27. How could comma separated initialization such as in Eigen be possibly implemented in C++?
  28. Can undefined behavior erase the hard drive?
  29. Is uninitialized data behavior well specified?
  30. C++ function called without object initialization

Leave a Comment