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std::isdigit(3) C++ Standard Libary std::isdigit(3) NAME std::isdigit - std::isdigit Synopsis Defined in header <cctype> int isdigit( int ch ); 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. Parameters ch - character to classify Return value Non-zero value if the character is a numeric character, zero other- wise. Notes isdigit and isxdigit are the only standard narrow character classi- fication functions that are not affected by the currently installed C locale. although some implementations (e.g. Microsoft in 1252 codepage) may classify addi- tional 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 ); } See also isdigit(std::locale) checks if a character is classified as a digit by a locale (function template) iswdigit checks if a wide character is a digit (function) C documentation for isdigit ASCII values characters iscntrl isprint isspace isblank isgraph ispunct isalnum isalpha isupper islower isdigit isxdigit decimal hexadecimal octal iswcntrl isw- print iswspace iswblank iswgraph iswpunct iswalnum iswalpha iswupper iswlower iswdigit iswxdigit 08 \x0\x8 \0\10 control codes 0 0 0 0 0 0 0 0 0 0 0 0 (NUL, etc.) 9 \x9 \11 tab (\t) 0 0 0 0 0 0 0 0 0 0 0 0 whitespaces 1013 \xA\xD \12\15 (\n, \v, \f, 0 0 0 0 0 0 0 0 0 0 0 0 \r) 1431 \xE\x1F \16\37 control codes 0 0 0 0 0 0 0 0 0 0 0 0 32 \x20 \40 space 0 0 0 0 0 0 0 0 0 0 0 0 3347 \x21\x2F \41\57 !"#$%&'()*+,-./ 0 0 0 0 0 0 0 0 0 0 0 0 4857 \x30\x39 \60\71 0123456789 0 0 0 0 0 0 0 0 0 0 0 0 5864 \x3A\x40 \72\100 :;<=>?@ 0 0 0 0 0 0 0 0 0 0 0 0 6570 \x41\x46 \101\106 ABCDEF 0 0 0 0 0 0 0 0 0 0 0 0 7190 \x47\x5A \107\132 GHIJKLMNOP 0 0 0 0 0 0 0 0 0 0 0 0 QRSTUVWXYZ 9196 \x5B\x60 \133\140 [\]^_` 0 0 0 0 0 0 0 0 0 0 0 0 97102 \x61\x66 \141\146 abcdef 0 0 0 0 0 0 0 0 0 0 0 0 103122 \x67\x7A \147\172 ghijklmnop 0 0 0 0 0 0 0 0 0 0 0 0 qrstuvwxyz 123126 \x7B\x7E \172\176 {|}~ 0 0 0 0 0 0 0 0 0 0 0 0 127 \x7F \177 backspace 0 0 0 0 0 0 0 0 0 0 0 0 character (DEL) http://cppreference.com 2024.06.10 std::isdigit(3)
NAME | Synopsis | Parameters | Return value | Notes | See also
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