CS253 Limits

C integral types

`<limits.h>`, alias `<climits>`
Symbol	Meaning
`CHAR_BIT`	Number of bits in a `char`
`SCHAR_MIN`…`SCHAR_MAX`	Range of `signed char`
`UCHAR_MAX`	Max value of `unsigned char`
`CHAR_MIN`…`CHAR_MAX`	Range of `char`
`SHRT_MIN`…`SHRT_MAX`	Range of `short int`
`USHRT_MAX`	Max value of `unsigned short int`
`INT_MIN`…`INT_MAX`	Range of `int`
`UINT_MAX`	Max value of `unsigned int`
`LONG_MIN`…`LONG_MAX`	Range of `long int`
`ULONG_MAX`	Max value of `unsigned long int`
`LLONG_MIN`…`LLONG_MAX`	Range of `long long int`
`ULLONG_MAX`	Max value of `unsigned long long int`

C floating-point types

`<float.h>`, alias `<cfloat>`
Symbol	Meaning
`FLT_DIG`	Mantissa decimal digits (`float`)
`DBL_DIG`	Mantissa decimal digits (`double`)
`LDBL_DIG`	Mantissa decimal digits (`long double`)
`FLT_MIN_10_EXP`…`FLT_MAX_10_EXP`	Exponent range (`float`)
`DBL_MIN_10_EXP`…`DBL_MAX_10_EXP`	Exponent range (`double`)
`LDBL_MIN_10_EXP`…`LDBL_MAX_10_EXP`	Exponent range (`long double`)
`FLT_MIN`…`FLT_MAX`	Value range (`float`)
`DBL_MIN`…`DBL_MAX`	Value range (`double`)
`LDBL_MIN`…`LDBL_MAX`	Value range (`long double`)

Pop Quiz

Quick, now:

What symbol says how many decimal digits are in the exponent of a long double?
What symbol gives the maximum value of a short?
What symbol gives the maximum value of a size_t?

C++ way

<limits> defines the template class numeric_limits, which is specialized for all built-in types. It has many static methods and constants, including:

.min()
.max()
.digits10
.min_exponent10
.max_exponent10

It is not clear why .min() and .max() are not constants. Surely, these values are known at compile-time. In fact, for C++11, they’re all constexpr. Fine.

Integral Example

cout << numeric_limits<int>::digits10 << ' '
     << numeric_limits<int>::min() << ' '
     << numeric_limits<int>::max() << '\n';

9 -2147483648 2147483647

Note the ::. We’d use . if we had an instance of this class.
digits10 is a constant, not a method.

Floating-Point Examples

typedef numeric_limits<float> nl;
cout << nl::digits10 << ' ' << nl::min() << ' ' << nl::max() << '\n';

6 1.17549e-38 3.40282e+38

using nl = numeric_limits<double>;
cout << nl::digits10 << ' ' << nl::min() << ' ' << nl::max() << '\n';

15 2.22507e-308 1.79769e+308

auto nl = numeric_limits<long double>();    // an instance
cout << nl.digits10 << ' ' << nl.min() << ' ' << nl.max() << '\n';

18 3.3621e-4932 1.18973e+4932

A Mystery

Why do these both compile? One must be wrong!

cout << numeric_limits<unsigned short>::min   << '\n';
cout << numeric_limits<unsigned short>::min() << '\n';

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CS253: Software Development with C++

Fall 2018

Limits