What's the C++ equivalent of UINT32_MAX?

问题

In C99, I include stdint.h and that gives me UINT32_MAX as well as uint32_t. However, in C++ the UINT32_MAX gets defined out. I can define __STDC_LIMIT_MACROS before including stdint.h, but this doesn't work if someone is including my header after already including stdint.h themselves.

So in C++, what's the standard way of finding out the maximum value representable in a uint32_t?

回答1:

Well, I don't know about uint32_t but for the fundamental types (bool, char, signed char, unsigned char, wchar_t, short, unsigned short, int, unsigned int, long, unsigned long, float, double and long double) you should use the numeric_limits templates via #include <limits>.

cout << "Minimum value for int: " << numeric_limits<int>::min() << endl;
cout << "Maximum value for int: " << numeric_limits<int>::max() << endl;

If uint32_t is a #define of one of the above than this code should work out of the box

    cout << "Maximum value for uint32_t: " << numeric_limits<uint32_t>::max() << endl;

回答2:

std::numeric_limits<T>::max() defines the maximum value for type T.

回答3:

Well, uint32_t will always be 32 bit, and always be unsigned, so you can safely define it manually:

#define UINT32_MAX  (0xffffffff)

You can also do

#define UINT32_MAX  ((uint32_t)-1)

回答4:

You may be able to eliminate the #include order problems by changing your build process to define the __STDC_LIMIT_MACROS symbol on the compiler command line instead:

cxx -D__STDC_LIMIT_MACROS ...

Of course, you would still have trouble if a header #undefs this symbol.

Also, the authors of the standard library implementation that you are using might not have intended for users to set that particular symbol; there might be a compiler flag or a different symbol that users are intended to use to enable C99 types in C++.

回答5:

I can't comment so here is my input on Glen vs Lior Kogan's answer.

If you are using static variables you will run into the problem that if you assign a constant value inside a class to numeric_limits::max() that value will be in fact set to zero because of the order of initialization (see this post zero initialization and static initialization of local scope static variable)

So in that case it will only work by using Lior Kogan's answer.

// This looks cleaner, less error prone and easier to read than the other suggested by Lior Kogan
#define UINT32_MAX  ((uint32_t)-1)

来源：https://stackoverflow.com/questions/1471353/whats-the-c-equivalent-of-uint32-max