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Checks if the given character is a hexadecimal numeric character (0123456789ABCDEFabcdef).

The behavior is undefined if the value of ch is not representable as unsigned char and is not equal to EOF .

[edit] Parameters

[edit] Return value

Non-zero value if the character is a hexadecimal numeric character, zero otherwise.

[edit] Notes

std::isdigit and std::isxdigit are the only standard narrow character classification functions that are not affected by the currently installed C locale. although some implementations (e.g. Microsoft in 1252 codepage) may classify additional single-byte characters as digits.

Like all other functions from <cctype>, the behavior of std::isxdigit is undefined if the argument's value is neither representable as unsigned char nor equal to EOF . To use these functions safely with plain chars (or signed chars), the argument should first be converted to unsigned char:

bool my_isxdigit(char ch)
{
 return std::isxdigit(static_cast<unsigned char>(ch));
}

Similarly, they should not be directly used with standard algorithms when the iterator's value type is char or signed char. Instead, convert the value to unsigned char first:

int count_xdigits(const std::string & s)
{
 return std::count_if (s.begin(), s.end(),
 // static_cast<int(*)(int)>(std::isxdigit) // wrong
 // [](int c){ return std::isxdigit(c); } // wrong
 // [](char c){ return std::isxdigit(c); } // wrong
 [](unsigned char c){ return std::isxdigit(c); } // correct
 );
}

[edit] Example

#include <cctype>
#include <climits>
#include <iostream>
 
int main()
{
 for (int c = 0; UCHAR_MAX >= c; ++c)
 if (isxdigit(c))
 std::cout << static_cast<char>(c);
 std::cout << '\n';
}

0123456789ABCDEFabcdef

[edit] See also

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