std::isgraph

int isgraph( int ch );

Checks if the given character is graphic (has a graphical representation) as classified by the currently installed C locale. In the default C locale, the following characters are graphic:

• digits (0123456789)
• uppercase letters (ABCDEFGHIJKLMNOPQRSTUVWXYZ)
• lowercase letters (abcdefghijklmnopqrstuvwxyz)
• punctuation characters (!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~)

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

Parameters

Return value

Non-zero value if the character has a graphical representation character, zero otherwise.

Notes

Like all other functions from <cctype>, the behavior of std::isgraph 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_isgraph(char ch)
{
    return std::isgraph(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_graphs(const std::string& s)
{
    return std::count_if(s.begin(), s.end(), 
                      // static_cast<int(*)(int)>(std::isgraph)         // wrong
                      // [](int c){ return std::isgraph(c); }           // wrong
                      // [](char c){ return std::isgraph(c); }          // wrong
                         [](unsigned char c){ return std::isgraph(c); } // correct
                        );
}

Example

#include <cctype>
#include <clocale>
#include <iostream>
 
int main()
{
    unsigned char c = '\xb6'; // the character ¶ in ISO-8859-1
 
    std::cout << "isgraph(\'\\xb6\', default C locale) returned "
              << std::boolalpha << (bool)std::isgraph(c) << '\n';
 
    std::setlocale(LC_ALL, "en_GB.iso88591");
    std::cout << "isgraph(\'\\xb6\', ISO-8859-1 locale) returned "
              << std::boolalpha << (bool)std::isgraph(c) << '\n';
}

isgraph('\xb6', default C locale) returned false
isgraph('\xb6', ISO-8859-1 locale) returned true

See also