Where are the limits for Qt types?

Question

Regularly, I could reference limits.h to see what the max is for a certain type, like an int or long.

In Qt, there are types like qlonglong. Is there a header file

Answer 1

Take a look at the QtGlobal documentation.

For some of the non-obvious ones:
qlonglong - 64-bit
qptrdiff - 32-bit or 64-bit depending on platform
qreal - double (float on ARM architectures)
quintptr - unsigned 32-bit or 64-bit depending on platform
qulonglong - unsigned 64-bit
uchar, uint, ulong, ushort - convenience shorthand for unsigned types

Answer 2

There's a high likelihood the Qt types distill down to one of the basic types for which numeric_limits are defined. Have you tried calling e.g., std::numeric_limits<qlonglong>::max()?

As MSalters points out, too, if the types are not builtin numeric_limits can still be specialized for them. If that were the case one would hope Qt would include them.