How VC++ and G++ treat uninitialized variables

Here is a sample code that demonstrates a basic C++ application and the different behavior represented by Visual C++ and GCC compilers regrading uninitialized variables

 #include  #include   #define LEARN_UNINITIZLIED_REAL_TYPES  //main can return void or int for VC compiler //main has to return int for GCC compiler int main() { #ifdef LEARN_UNINITIALIZED_INT  int iIsInitialized = 123;  printf("iIsInitialized = %d\n", iIsInitialized);   //Some random value  auto int iautoUninitialized;  //Warning C4700 from VC at compile time, exception         //at run-time (run-time check failure) -858993460  //No warning from GCC, no exception at run-time:         //the value is 1628438944  printf("iautoUninitialized = %d\n", iautoUninitialized);   //Some random value  int iUninitialized;  //Warning C4700 from VC at compile time, exception         //at run-time (run-time check failure) -858993460  //No warning from GCC, no exception at run-time:         //the value is 0 (after we call the previous auto         //value it becomes zero)  printf("iUninitialized = %d\n", iUninitialized); #endif  #ifdef LEARN_UNINITIZLIED_POINTERS  //C4700 from VC compiler, First run-time check         //failure that can be supassed but after that         //we get access violation exception  //that terminates the application  //GCC doesn't complain and actually runs         //it and shows some value  auto int* myIninitializePointerToInt;  printf("myIninitializePointerToInt = %d\n",                *myIninitializePointerToInt); #endif  #ifdef LEARN_UNINITIZLIED_REAL_TYPES  //Unlike integer ojbects, real number objects         //can contain values that correspond to         //no genuine number like NAN  //NAN (Not a number), math.h has especial         //implementation defined values corresponding         //to no actual real numbers.  float fNAN = log((float)-2);   //VCC: -1.#IND00  //GCC: -inf  printf("fNAN = %f\n", fNAN); #endif   return 0; } //For GCC compiler there must be a new line //at the end of file