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

The behavior is undefined if the value ofch is not representable asunsignedchar and is not equal toEOF.

[edit]Parameters

[edit]Return value

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

[edit]Notes

isdigit andisxdigit are the only standard narrow character classification functions that are not affected by the currently installed C locale. although some implementations (e.g. Microsoft in1252 codepage) may classify additional single-byte characters as digits.

Like all other functions from<cctype>, the behavior ofstd::isdigit is undefined if the argument's value is neither representable asunsignedchar nor equal toEOF. To use these functions safely with plainchars (orsignedchars), the argument should first be converted tounsignedchar:

bool my_isdigit(char ch){return std::isdigit(static_cast<unsignedchar>(ch));}

Similarly, they should not be directly used with standard algorithms when the iterator's value type ischar orsignedchar. Instead, convert the value tounsignedchar first:

int count_digits(conststd::string& s){returnstd::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[](unsignedchar c){return std::isdigit(c);}// correct);}

[edit]Example

#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<unsignedchar>(i);std::cout<<'\n';}

0123456789

[edit]See also

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