std::isprint

int isprint( int ch );

Checks if ch is a printable character as classified by the currently installed C locale. In the default, "C" locale, the following characters are printable:

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

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 can be printed, zero otherwise.

Notes

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

Example

#include <cctype>
#include <clocale>
#include <iostream>
 
int main()
{
    unsigned char c = '\xa0'; // the non-breaking space in ISO-8859-1
 
    std::cout << "isprint(\'\\xa0\', default C locale) returned "
              << std::boolalpha << (bool)std::isprint(c) << '\n';
 
    std::setlocale(LC_ALL, "en_GB.iso88591");
    std::cout << "isprint(\'\\xa0\', ISO-8859-1 locale) returned "
              << std::boolalpha << (bool)std::isprint(c) << '\n';
}

isprint('\xa0', default C locale) returned false
isprint('\xa0', ISO-8859-1 locale) returned true

See also