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std::numeric_limits<T>::max_exponent10 - cppreference.com

From cppreference.com

static const int max_exponent10;

 (until C++11)

static constexpr int max_exponent10;

 (since C++11)

The value of std::numeric_limits<T>::max_exponent10 is the largest positive number n such that 10n
 is a representable finite value of the floating-point type T.

Standard specializations

T value of std::numeric_limits<T>::max_exponent10
/* non-specialized */ 0
bool 0
char 0
signed char 0
unsigned char 0
wchar_t 0
char8_t (since C++20) 0
char16_t (since C++11) 0
char32_t (since C++11) 0
short 0
unsigned short 0
int 0
unsigned int 0
long 0
unsigned long 0
long long (since C++11) 0
unsigned long long (since C++11) 0
float FLT_MAX_10_EXP
double DBL_MAX_10_EXP
long double LDBL_MAX_10_EXP

Example

Demonstrates the relationships of max_exponent, max_exponent10, and max() for the type float:

#include <iostream>
#include <limits>

int main()
{
    std::cout << "max() = " << std::numeric_limits<float>::max() << '\n'
              << "max_exponent10 = " << std::numeric_limits<float>::max_exponent10 << '\n'
              << std::hexfloat << '\n'
              << "max() = " << std::numeric_limits<float>::max() << '\n'
              << "max_exponent = " << std::numeric_limits<float>::max_exponent << '\n';
}

Output: 

max() = 3.40282e+38
max_exponent10 = 38

max() = 0x1.fffffep+127
max_exponent = 128

See also

one more than the largest integer power of the radix that is a valid finite floating-point value
(public static member constant) [edit]
one more than the smallest negative power of the radix that is a valid normalized floating-point value
(public static member constant) [edit]
the smallest negative power of ten that is a valid normalized floating-point value
(public static member constant) [edit]