CODEWITHSUNDEEP
c#c++casting
SvalinnAsgard
SvalinnAsgard

Reputation: 225

Purpose of casting -1 to uint32?

This is probably a really silly question to experienced C++ developers, but what is the purpose of casting a -1 to uint32? I am translating a program from C++ to C# and there are many occasions when I see something like this:

static const uint32 AllTypes = static_cast<uint32>(-1);

What exactly does this do? How can the same be accomplished in C#?

Upvotes: 4

Views: 2371

Answers (3)

fredoverflow
fredoverflow

Reputation: 263320

How can the same be accomplished in C#

uint AllTypes = uint.MaxValue;

Upvotes: 2

CodesInChaos
CodesInChaos

Reputation: 108840

On systems using two's complement, casting -1 to unsigned gives the highest value an unsigned number can represent.

In C# you can use unchecked((UInt32)-1) or better: UInt32.MaxValue. This is well defined behavior, and works on all CPU architectures.

According to the thread rve linked, casting -1 to unsigned results in all bits being set on all architectures in C++.

Upvotes: 4

CapelliC
CapelliC

Reputation: 60034

I guess it's used to have all bits to 1. Useful when we use tagged data. Probably each elementary type it's given a bit, and 'complex' types (arrays, for instance) get their own.

Upvotes: 1

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