Home - News ( United States | United Kingdom | Italy | Germany ) - Football scores

Showing content from https://en.cppreference.com/w/cpp/language/../types/../string/byte/isdigit.html below:

std::isdigit - cppreference.com

Checks if the given character is one of the 10 decimal digits: (0123456789).

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

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

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

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

Output:

iscntrl
iswcntrl

isprint
iswprint

isspace
iswspace

isblank
iswblank

isgraph
iswgraph

ispunct
iswpunct

isalnum
iswalnum

isalpha
iswalpha

isupper
iswupper

islower
iswlower

isdigit
iswdigit

isxdigit
iswxdigit

RetroSearch is an open source project built by @garambo | Open a GitHub Issue

Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo

HTML: 3.2 | Encoding: UTF-8 | Version: 0.7.4