G ++ 4.4“未初始化”变量

Question

I am using g++ on Ubuntu 10.10(64-bit) if the OS is at all relevant for the matter. I saw something strange so i decided to check and for some reason this code

#include <iostream>

int main()
{
    int a;

    std::cout << a << std::endl;

    return 0;
}

always prints 0. Obviously g++ does auto initialization of uninitialized variables to their corresponding null-value. The thing is I want to turn that feature off, or at least make g++ show warning about using uninitialized variables, since this way my code won't work well when compiled on VS for instance. Besides I'm pretty sure the C++ standard states that a variable which isn't implicitly initialized with some value has an undefined value amongst all it's possible values, which should in fact be different with every execution of the program, since different parts of the operating memory are used every time it's executed.

Explicit question: Is there a way to make g++ show warnings for uninitialized variables?

Answer 1

GCC does not initialize uninitialized variables to 0. It's just a case that a is 0 .

If what you want to do is to receive warnings when you use uninitialized variables you could use GCC option -Wuninitialized (also included by -Wall ).

However it can't statically spot any possible usage of uninitialized variables: you'll need some run time tools to spot that, and there's valgrind for this.

Answer 2

You might also try to use a tool like cppcheck . In general, in well written C++ there is rarely a reason to declare a variable without initializing it.