C++ Default value for bool

No, primitives, including bool, are not guaranteed to be initialized to any particular value in the general case.

i see.
Don't know where/when i formed this idea about it. Glad i've run into this.

thanx SiCrane.

There are no default values in C++ for primitive types. You are just getting whatever happened in be in memory at that location. Debugger's will usually initialize stuff to default values.

I think bools are initialized to 0 if they're globals.

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Original post by filipe I think bools are initialized to 0 if they're globals.

It would seem to apply for all globals then.
At least my combination of bools and ints all got zero as their initial values.
Or its just that, the whole datasegment is just by default zeroed?

This happened on Visual Studios debug mode though...
Wonder if enabling optimizations and disabling runtime checkups would alter the result.

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I think bools are initialized to 0 if they're globals.

Under no circumstances would I recommend you ever rely on this being the case.

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Under no circumstances would I recommend you ever rely on this being the case.

It is reliable; objects with static storage duration are zero-initialized before all other initialization occurs (see 'basic.start.init' in the standard).

Only for certain values of "reliable" though. Try running this with MSVC 2008:

struct Foo {};int Foo::* data;int main() {  std::cout << (data == 0) << std::endl;}

I'm firmly in the "just initialize your variables" camp.

Just don't be lazy, if you need something initialized to a particular value, do it explicitly yourself, it really isn't that much of a deal to write:

bool var = false;

instead of

bool var;

or is it?

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Original post by Kwizatz Just don't be lazy, if you need something initialized to a particular value, do it explicitly yourself, it really isn't that much of a deal to write: bool var = false; instead of bool var; or is it?

It is, when you have an array. (Real programmers probably cry in pain while reading this)

bool array[100] = {};

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Original post by DevFred bool array[100] = {};

bool* array = new bool[100]();

too...

In general, always initialize your variables, never just leave it up to the compiler (even for statics), because interpretations of the standard varies from compiler to compiler, and even version to version. Just spare yourself the hassle and initialize them yourself.

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Original post by DevFred bool array[100] = {};

Hmmm. I learn something new every day. Thanks guys!

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Original post by pauls_1979 Quote: I think bools are initialized to 0 if they're globals. Under no circumstances would I recommend you ever rely on this being the case.

afaik, this is something you can rely on. anything with static duration will be 0'd, guaranteed.

static int magic[32] = { 0, 1, 2, 3 };

will end up 01230000...

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Original post by clashie anything with static duration will be 0'd, guaranteed.

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Original post by SiCrane Try running this with MSVC 2008: struct Foo {};int Foo::* data;int main() { std::cout << (data == 0) << std::endl;}

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static int magic[32] = { 0, 1, 2, 3 }; will end up 01230000...

Which doesn't rely on the zero-initialization of objects with static storage duration. If you specify four items in an aggregate initializer list for an array of 32 ints, you aren't saying leave the items you didn't specify uninitialized, you're saying initialize the rest of the other items with 0.

Uninitialized statics are stored in the .bss section of the program and the loader knows to initialize these variables to 0. However, if the static is actually placed in the .bss section might be compiler specific so to be safe you should probably just initialize it yourself.